The kernel’s command-line parameters — The Linux Kernel documentation (2023)

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The following is a consolidated list of the kernel parameters as implementedby the __setup(), early_param(), core_param() and module_param() macrosand sorted into English Dictionary order (defined as ignoring allpunctuation and sorting digits before letters in a case insensitivemanner), and with descriptions where known.

The kernel parses parameters from the kernel command line up to “--“;if it doesn’t recognize a parameter and it doesn’t contain a ‘.’, theparameter gets passed to init: parameters with ‘=’ go into init’senvironment, others are passed as command line arguments to init.Everything after “--” is passed as an argument to init.

Module parameters can be specified in two ways: via the kernel commandline with a module name prefix, or via modprobe, e.g.:

(kernel command line) usbcore.blinkenlights=1(modprobe command line) modprobe usbcore blinkenlights=1

Parameters for modules which are built into the kernel need to bespecified on the kernel command line. modprobe looks through thekernel command line (/proc/cmdline) and collects module parameterswhen it loads a module, so the kernel command line can be used forloadable modules too.

Hyphens (dashes) and underscores are equivalent in parameter names, so:

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can also be entered as:

log-buf-len=1M print_fatal_signals=1

Double-quotes can be used to protect spaces in values, e.g.:

param="spaces in here"

cpu lists:

Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,nohz_full, irqaffinity, rcu_nocbs. The format of this list is:

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<cpu number>,…,<cpu number>


<cpu number>-<cpu number>(must be a positive range in ascending order)

or a mixture

<cpu number>,…,<cpu number>-<cpu number>

Note that for the special case of a range one can split the range into equalsized groups and for each group use some amount from the beginning of thatgroup:

<cpu number>-<cpu number>:<used size>/<group size>

For example one can add to the command line following parameter:


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where the final item represents CPUs 100,101,125,126,150,151,…

The value “N” can be used to represent the numerically last CPU on the system,i.e “foo_cpus=16-N” would be equivalent to “16-31” on a 32 core system.

Keep in mind that “N” is dynamic, so if system changes cause the bitmap widthto change, such as less cores in the CPU list, then N and any ranges using Nwill also change. Use the same on a small 4 core system, and “16-N” becomes“16-3” and now the same boot input will be flagged as invalid (start > end).

The special case-tolerant group name “all” has a meaning of selecting all CPUs,so that “nohz_full=all” is the equivalent of “nohz_full=0-N”.

The semantics of “N” and “all” is supported on a level of bitmaps and holds forall users of bitmap_parse().

This document may not be entirely up to date and comprehensive. The command“modinfo -p ${modulename}” shows a current list of all parameters of a loadablemodule. Loadable modules, after being loaded into the running kernel, alsoreveal their parameters in /sys/module/${modulename}/parameters/. Some of theseparameters may be changed at runtime by the commandecho -n ${value} > /sys/module/${modulename}/parameters/${parm}.

The parameters listed below are only valid if certain kernel build options wereenabled and if respective hardware is present. The text in square brackets atthe beginning of each description states the restrictions within which aparameter is applicable:

ACPI ACPI support is enabled.AGP AGP (Accelerated Graphics Port) is enabled.ALSA ALSA sound support is enabled.APIC APIC support is enabled.APM Advanced Power Management support is enabled.APPARMOR AppArmor support is enabled.ARM ARM architecture is enabled.ARM64 ARM64 architecture is enabled.AX25 Appropriate AX.25 support is enabled.CLK Common clock infrastructure is enabled.CMA Contiguous Memory Area support is enabled.DRM Direct Rendering Management support is enabled.DYNAMIC_DEBUG Build in debug messages and enable them at runtimeEDD BIOS Enhanced Disk Drive Services (EDD) is enabledEFI EFI Partitioning (GPT) is enabledEVM Extended Verification ModuleFB The frame buffer device is enabled.FTRACE Function tracing enabled.GCOV GCOV profiling is enabled.HIBERNATION HIBERNATION is enabled.HW Appropriate hardware is enabled.HYPER_V HYPERV support is enabled.IA-64 IA-64 architecture is enabled.IMA Integrity measurement architecture is enabled.IP_PNP IP DHCP, BOOTP, or RARP is enabled.IPV6 IPv6 support is enabled.ISAPNP ISA PnP code is enabled.ISDN Appropriate ISDN support is enabled.ISOL CPU Isolation is enabled.JOY Appropriate joystick support is enabled.KGDB Kernel debugger support is enabled.KVM Kernel Virtual Machine support is enabled.LIBATA Libata driver is enabledLP Printer support is enabled.LOOP Loopback device support is enabled.M68k M68k architecture is enabled. These options have more detailed description inside of Documentation/m68k/kernel-options.rst.MDA MDA console support is enabled.MIPS MIPS architecture is enabled.MOUSE Appropriate mouse support is enabled.MSI Message Signaled Interrupts (PCI).MTD MTD (Memory Technology Device) support is enabled.NET Appropriate network support is enabled.NUMA NUMA support is enabled.NFS Appropriate NFS support is enabled.OF Devicetree is enabled.PV_OPS A paravirtualized kernel is enabled.PARISC The PA-RISC architecture is enabled.PCI PCI bus support is enabled.PCIE PCI Express support is enabled.PCMCIA The PCMCIA subsystem is enabled.PNP Plug & Play support is enabled.PPC PowerPC architecture is enabled.PPT Parallel port support is enabled.PS2 Appropriate PS/2 support is enabled.RAM RAM disk support is enabled.RISCV RISCV architecture is enabled.RDT Intel Resource Director Technology.S390 S390 architecture is enabled.SCSI Appropriate SCSI support is enabled. A lot of drivers have their options described inside the Documentation/scsi/ sub-directory.SECURITY Different security models are enabled.SELINUX SELinux support is enabled.SERIAL Serial support is enabled.SH SuperH architecture is enabled.SMP The kernel is an SMP kernel.SPARC Sparc architecture is enabled.SWSUSP Software suspend (hibernation) is enabled.SUSPEND System suspend states are enabled.TPM TPM drivers are enabled.UMS USB Mass Storage support is enabled.USB USB support is enabled.USBHID USB Human Interface Device support is enabled.V4L Video For Linux support is enabled.VMMIO Driver for memory mapped virtio devices is enabled.VGA The VGA console has been enabled.VT Virtual terminal support is enabled.WDT Watchdog support is enabled.X86-32 X86-32, aka i386 architecture is enabled.X86-64 X86-64 architecture is enabled. More X86-64 boot options can be found in Documentation/x86/x86_64/boot-options.rst.X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)X86_UV SGI UV support is enabled.XEN Xen support is enabledXTENSA xtensa architecture is enabled.
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In addition, the following text indicates that the option:

BUGS= Relates to possible processor bugs on the said processor.KNL Is a kernel start-up parameter.BOOT Is a boot loader parameter.

Parameters denoted with BOOT are actually interpreted by the bootloader, and have no meaning to the kernel directly.Do not modify the syntax of boot loader parameters without extremeneed or coordination with <The Linux/x86 Boot Protocol>.

There are also arch-specific kernel-parameters not documented here.See for example <AMD64 Specific Boot Options>.

Note that ALL kernel parameters listed below are CASE SENSITIVE, and thata trailing = on the name of any parameter states that that parameter willbe entered as an environment variable, whereas its absence indicates thatit will appear as a kernel argument readable via /proc/cmdline by programsrunning once the system is up.

The number of kernel parameters is not limited, but the length of thecomplete command line (parameters including spaces etc.) is limited toa fixed number of characters. This limit depends on the architectureand is between 256 and 4096 characters. It is defined in the file./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.

Finally, the [KMG] suffix is commonly described after a number of kernelparameter values. These ‘K’, ‘M’, and ‘G’ letters represent the _binary_multipliers ‘Kilo’, ‘Mega’, and ‘Giga’, equaling 2^10, 2^20, and 2^30bytes respectively. Such letter suffixes can also be entirely omitted:

 acpi= [HW,ACPI,X86,ARM64] Advanced Configuration and Power Interface Format: { force | on | off | strict | noirq | rsdt | copy_dsdt } force -- enable ACPI if default was off on -- enable ACPI but allow fallback to DT [arm64] off -- disable ACPI if default was on noirq -- do not use ACPI for IRQ routing strict -- Be less tolerant of platforms that are not strictly ACPI specification compliant. rsdt -- prefer RSDT over (default) XSDT copy_dsdt -- copy DSDT to memory For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" are available See also Documentation/power/runtime_pm.rst, pci=noacpi acpi_apic_instance= [ACPI, IOAPIC] Format: <int> 2: use 2nd APIC table, if available 1,0: use 1st APIC table default: 0 acpi_backlight= [HW,ACPI] { vendor | video | native | none } If set to vendor, prefer vendor-specific driver (e.g. thinkpad_acpi, sony_acpi, etc.) instead of the ACPI video.ko driver. If set to video, use the ACPI video.ko driver. If set to native, use the device's native backlight mode. If set to none, disable the ACPI backlight interface. acpi_force_32bit_fadt_addr force FADT to use 32 bit addresses rather than the 64 bit X_* addresses. Some firmware have broken 64 bit addresses for force ACPI ignore these and use the older legacy 32 bit addresses. acpica_no_return_repair [HW, ACPI] Disable AML predefined validation mechanism This mechanism can repair the evaluation result to make the return objects more ACPI specification compliant. This option is useful for developers to identify the root cause of an AML interpreter issue when the issue has something to do with the repair mechanism. acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] acpi.debug_level= [HW,ACPI,ACPI_DEBUG] Format: <int> CONFIG_ACPI_DEBUG must be enabled to produce any ACPI debug output. Bits in debug_layer correspond to a _COMPONENT in an ACPI source file, e.g., #define _COMPONENT ACPI_EVENTS Bits in debug_level correspond to a level in ACPI_DEBUG_PRINT statements, e.g., ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... The debug_level mask defaults to "info". See Documentation/firmware-guide/acpi/debug.rst for more information about debug layers and levels. Enable processor driver info messages: acpi.debug_layer=0x20000000 Enable AML "Debug" output, i.e., stores to the Debug object while interpreting AML: acpi.debug_layer=0xffffffff acpi.debug_level=0x2 Enable all messages related to ACPI hardware: acpi.debug_layer=0x2 acpi.debug_level=0xffffffff Some values produce so much output that the system is unusable. The "log_buf_len" parameter may be useful if you need to capture more output. acpi_enforce_resources= [ACPI] { strict | lax | no } Check for resource conflicts between native drivers and ACPI OperationRegions (SystemIO and SystemMemory only). IO ports and memory declared in ACPI might be used by the ACPI subsystem in arbitrary AML code and can interfere with legacy drivers. strict (default): access to resources claimed by ACPI is denied; legacy drivers trying to access reserved resources will fail to bind to device using them. lax: access to resources claimed by ACPI is allowed; legacy drivers trying to access reserved resources will bind successfully but a warning message is logged. no: ACPI OperationRegions are not marked as reserved, no further checks are performed. acpi_force_table_verification [HW,ACPI] Enable table checksum verification during early stage. By default, this is disabled due to x86 early mapping size limitation. acpi_irq_balance [HW,ACPI] ACPI will balance active IRQs default in APIC mode acpi_irq_nobalance [HW,ACPI] ACPI will not move active IRQs (default) default in PIC mode acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA Format: <irq>,<irq>... acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for use by PCI Format: <irq>,<irq>... acpi_mask_gpe= [HW,ACPI] Due to the existence of _Lxx/_Exx, some GPEs triggered by unsupported hardware/firmware features can result in GPE floodings that cannot be automatically disabled by the GPE dispatcher. This facility can be used to prevent such uncontrolled GPE floodings. Format: <byte> or <bitmap-list> acpi_no_auto_serialize [HW,ACPI] Disable auto-serialization of AML methods AML control methods that contain the opcodes to create named objects will be marked as "Serialized" by the auto-serialization feature. This feature is enabled by default. This option allows to turn off the feature. acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump kernels. acpi_no_static_ssdt [HW,ACPI] Disable installation of static SSDTs at early boot time By default, SSDTs contained in the RSDT/XSDT will be installed automatically and they will appear under /sys/firmware/acpi/tables. This option turns off this feature. Note that specifying this option does not affect dynamic table installation which will install SSDT tables to /sys/firmware/acpi/tables/dynamic. acpi_no_watchdog [HW,ACPI,WDT] Ignore the ACPI-based watchdog interface (WDAT) and let a native driver control the watchdog device instead. acpi_rsdp= [ACPI,EFI,KEXEC] Pass the RSDP address to the kernel, mostly used on machines running EFI runtime service to boot the second kernel for kdump. acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS Format: To spoof as Windows 98: ="Microsoft Windows" acpi_rev_override [ACPI] Override the _REV object to return 5 (instead of 2 which is mandated by ACPI 6) as the supported ACPI specification revision (when using this switch, it may be necessary to carry out a cold reboot _twice_ in a row to make it take effect on the platform firmware). acpi_osi= [HW,ACPI] Modify list of supported OS interface strings acpi_osi="string1" # add string1 acpi_osi="!string2" # remove string2 acpi_osi=!* # remove all strings acpi_osi=! # disable all built-in OS vendor strings acpi_osi=!! # enable all built-in OS vendor strings acpi_osi= # disable all strings 'acpi_osi=!' can be used in combination with single or multiple 'acpi_osi="string1"' to support specific OS vendor string(s). Note that such command can only affect the default state of the OS vendor strings, thus it cannot affect the default state of the feature group strings and the current state of the OS vendor strings, specifying it multiple times through kernel command line is meaningless. This command is useful when one do not care about the state of the feature group strings which should be controlled by the OSPM. Examples: 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent to 'acpi_osi="Windows 2000" acpi_osi=!', they all can make '_OSI("Windows 2000")' TRUE. 'acpi_osi=' cannot be used in combination with other 'acpi_osi=' command lines, the _OSI method will not exist in the ACPI namespace. NOTE that such command can only affect the _OSI support state, thus specifying it multiple times through kernel command line is also meaningless. Examples: 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' FALSE. 'acpi_osi=!*' can be used in combination with single or multiple 'acpi_osi="string1"' to support specific string(s). Note that such command can affect the current state of both the OS vendor strings and the feature group strings, thus specifying it multiple times through kernel command line is meaningful. But it may still not able to affect the final state of a string if there are quirks related to this string. This command is useful when one want to control the state of the feature group strings to debug BIOS issues related to the OSPM features. Examples: 1. 'acpi_osi="Module Device" acpi_osi=!*' can make '_OSI("Module Device")' FALSE. 2. 'acpi_osi=!* acpi_osi="Module Device"' can make '_OSI("Module Device")' TRUE. 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is equivalent to 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' and 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', they all will make '_OSI("Windows 2000")' TRUE. acpi_pm_good [X86] Override the pmtimer bug detection: force the kernel to assume that this machine's pmtimer latches its value and always returns good values. acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode Format: { level | edge | high | low } acpi_skip_timer_override [HW,ACPI] Recognize and ignore IRQ0/pin2 Interrupt Override. For broken nForce2 BIOS resulting in XT-PIC timer. acpi_sleep= [HW,ACPI] Sleep options Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, s4_nohwsig, old_ordering, nonvs, sci_force_enable, nobl } See Documentation/power/video.rst for information on s3_bios and s3_mode. s3_beep is for debugging; it makes the PC's speaker beep as soon as the kernel's real-mode entry point is called. s4_hwsig causes the kernel to check the ACPI hardware signature during resume from hibernation, and gracefully refuse to resume if it has changed. This complies with the ACPI specification but not with reality, since Windows does not do this and many laptops do change it on docking. So the default behaviour is to allow resume and simply warn when the signature changes, unless the s4_hwsig option is enabled. s4_nohwsig prevents ACPI hardware signature from being used (or even warned about) during resume. old_ordering causes the ACPI 1.0 ordering of the _PTS control method, with respect to putting devices into low power states, to be enforced (the ACPI 2.0 ordering of _PTS is used by default). nonvs prevents the kernel from saving/restoring the ACPI NVS memory during suspend/hibernation and resume. sci_force_enable causes the kernel to set SCI_EN directly on resume from S1/S3 (which is against the ACPI spec, but some broken systems don't work without it). nobl causes the internal blacklist of systems known to behave incorrectly in some ways with respect to system suspend and resume to be ignored (use wisely). acpi_use_timer_override [HW,ACPI] Use timer override. For some broken Nvidia NF5 boards that require a timer override, but don't have HPET add_efi_memmap [EFI; X86] Include EFI memory map in kernel's map of available physical RAM. agp= [AGP] { off | try_unsupported } off: disable AGP support try_unsupported: try to drive unsupported chipsets (may crash computer or cause data corruption) ALSA [HW,ALSA] See Documentation/sound/alsa-configuration.rst alignment= [KNL,ARM] Allow the default userspace alignment fault handler behaviour to be specified. Bit 0 enables warnings, bit 1 enables fixups, and bit 2 sends a segfault. align_va_addr= [X86-64] Align virtual addresses by clearing slice [14:12] when allocating a VMA at process creation time. This option gives you up to 3% performance improvement on AMD F15h machines (where it is enabled by default) for a CPU-intensive style benchmark, and it can vary highly in a microbenchmark depending on workload and compiler. 32: only for 32-bit processes 64: only for 64-bit processes on: enable for both 32- and 64-bit processes off: disable for both 32- and 64-bit processes alloc_snapshot [FTRACE] Allocate the ftrace snapshot buffer on boot up when the main buffer is allocated. This is handy if debugging and you need to use tracing_snapshot() on boot up, and do not want to use tracing_snapshot_alloc() as it needs to be done where GFP_KERNEL allocations are allowed. allow_mismatched_32bit_el0 [ARM64] Allow execve() of 32-bit applications and setting of the PER_LINUX32 personality on systems where only a strict subset of the CPUs support 32-bit EL0. When this parameter is present, the set of CPUs supporting 32-bit EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 and hot-unplug operations may be restricted. See Documentation/arm64/asymmetric-32bit.rst for more information. amd_iommu= [HW,X86-64] Pass parameters to the AMD IOMMU driver in the system. Possible values are: fullflush - Deprecated, equivalent to iommu.strict=1 off - do not initialize any AMD IOMMU found in the system force_isolation - Force device isolation for all devices. The IOMMU driver is not allowed anymore to lift isolation requirements as needed. This option does not override iommu=pt force_enable - Force enable the IOMMU on platforms known to be buggy with IOMMU enabled. Use this option with care. pgtbl_v1 - Use v1 page table for DMA-API (Default). pgtbl_v2 - Use v2 page table for DMA-API. amd_iommu_dump= [HW,X86-64] Enable AMD IOMMU driver option to dump the ACPI table for AMD IOMMU. With this option enabled, AMD IOMMU driver will print ACPI tables for AMD IOMMU during IOMMU initialization. amd_iommu_intr= [HW,X86-64] Specifies one of the following AMD IOMMU interrupt remapping modes: legacy - Use legacy interrupt remapping mode. vapic - Use virtual APIC mode, which allows IOMMU to inject interrupts directly into guest. This mode requires kvm-amd.avic=1. (Default when IOMMU HW support is present.) [HW,JOY] Amiga joystick support Map of devices attached to JOY0DAT and JOY1DAT Format: <a>,<b> See also Documentation/input/joydev/joystick.rst [HW,JOY] Analog joystick and gamepad support Specifies type or capabilities of an analog joystick connected to one of 16 gameports Format: <type1>,<type2>,..<type16> apc= [HW,SPARC] Power management functions (SPARCstation-4/5 + deriv.) Format: noidle Disable APC CPU standby support. SPARCstation-Fox does not play well with APC CPU idle - disable it if you have APC and your system crashes randomly. apic= [APIC,X86] Advanced Programmable Interrupt Controller Change the output verbosity while booting Format: { quiet (default) | verbose | debug } Change the amount of debugging information output when initialising the APIC and IO-APIC components. For X86-32, this can also be used to specify an APIC driver name. Format: apic=driver_name Examples: apic=bigsmp apic_extnmi= [APIC,X86] External NMI delivery setting Format: { bsp (default) | all | none } bsp: External NMI is delivered only to CPU 0 all: External NMIs are broadcast to all CPUs as a backup of CPU 0 none: External NMI is masked for all CPUs. This is useful so that a dump capture kernel won't be shot down by NMI autoconf= [IPV6] See Documentation/networking/ipv6.rst. apm= [APM] Advanced Power Management See header of arch/x86/kernel/apm_32.c. apparmor= [APPARMOR] Disable or enable AppArmor at boot time Format: { "0" | "1" } See security/apparmor/Kconfig help text 0 -- disable. 1 -- enable. Default value is set via kernel config option. arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards Format: <io>,<irq>,<nodeID> arm64.nobti [ARM64] Unconditionally disable Branch Target Identification support arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication support arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension support arm64.nosve [ARM64] Unconditionally disable Scalable Vector Extension support arm64.nosme [ARM64] Unconditionally disable Scalable Matrix Extension support ataflop= [HW,M68k] atarimouse= [HW,MOUSE] Atari Mouse atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, EzKey and similar keyboards atkbd.reset= [HW] Reset keyboard during initialization atkbd.set= [HW] Select keyboard code set Format: <int> (2 = AT (default), 3 = PS/2) atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar keyboards atkbd.softraw= [HW] Choose between synthetic and real raw mode Format: <bool> (0 = real, 1 = synthetic (default)) atkbd.softrepeat= [HW] Use software keyboard repeat audit= [KNL] Enable the audit sub-system Format: { "0" | "1" | "off" | "on" } 0 | off - kernel audit is disabled and can not be enabled until the next reboot unset - kernel audit is initialized but disabled and will be fully enabled by the userspace auditd. 1 | on - kernel audit is initialized and partially enabled, storing at most audit_backlog_limit messages in RAM until it is fully enabled by the userspace auditd. Default: unset audit_backlog_limit= [KNL] Set the audit queue size limit. Format: <int> (must be >=0) Default: 64 bau= [X86_UV] Enable the BAU on SGI UV. The default behavior is to disable the BAU (i.e. bau=0). Format: { "0" | "1" } 0 - Disable the BAU. 1 - Enable the BAU. unset - Disable the BAU. baycom_epp= [HW,AX25] Format: <io>,<mode> baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem Format: <io>,<mode> See header of drivers/net/hamradio/baycom_par.c. baycom_ser_fdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Full Duplex Mode) Format: <io>,<irq>,<mode>[,<baud>] See header of drivers/net/hamradio/baycom_ser_fdx.c. baycom_ser_hdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Half Duplex Mode) Format: <io>,<irq>,<mode> See header of drivers/net/hamradio/baycom_ser_hdx.c. bert_disable [ACPI] Disable BERT OS support on buggy BIOSes. bgrt_disable [ACPI][X86] Disable BGRT to avoid flickering OEM logo. blkdevparts= Manual partition parsing of block device(s) for embedded devices based on command line input. See Documentation/block/cmdline-partition.rst boot_delay= Milliseconds to delay each printk during boot. Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, and you may also have to specify "lpj=". Boot_delay values larger than 10 seconds (10000) are assumed erroneous and ignored. Format: integer bootconfig [KNL] Extended command line options can be added to an initrd and this will cause the kernel to look for it. See Documentation/admin-guide/bootconfig.rst bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) Most important insmod options are available as kernel args too. bttv.pll= See Documentation/admin-guide/media/bttv.rst bttv.tuner= bulk_remove=off [PPC] This parameter disables the use of the pSeries firmware feature for flushing multiple hpte entries at a time. c101= [NET] Moxa C101 synchronous serial card cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. Sometimes CPU hardware bugs make them report the cache size incorrectly. The kernel will attempt work arounds to fix known problems, but for some CPUs it is not possible to determine what the correct size should be. This option provides an override for these situations. carrier_timeout= [NET] Specifies amount of time (in seconds) that the kernel should wait for a network carrier. By default it waits 120 seconds. ca_keys= [KEYS] This parameter identifies a specific key(s) on the system trusted keyring to be used for certificate trust validation. format: { id:<keyid> | builtin } cca= [MIPS] Override the kernel pages' cache coherency algorithm. Accepted values range from 0 to 7 inclusive. See arch/mips/include/asm/pgtable-bits.h for platform specific values (SB1, Loongson3 and others). ccw_timeout_log [S390] See Documentation/s390/common_io.rst for details. cgroup_disable= [KNL] Disable a particular controller or optional feature Format: {name of the controller(s) or feature(s) to disable} The effects of cgroup_disable=foo are: - foo isn't auto-mounted if you mount all cgroups in a single hierarchy - foo isn't visible as an individually mountable subsystem - if foo is an optional feature then the feature is disabled and corresponding cgroup files are not created {Currently only "memory" controller deal with this and cut the overhead, others just disable the usage. So only cgroup_disable=memory is actually worthy} Specifying "pressure" disables per-cgroup pressure stall information accounting feature cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 Format: { { controller | "all" | "named" } [,{ controller | "all" | "named" }...] } Like cgroup_disable, but only applies to cgroup v1; the blacklisted controllers remain available in cgroup2. "all" blacklists all controllers and "named" disables named mounts. Specifying both "all" and "named" disables all v1 hierarchies. cgroup.memory= [KNL] Pass options to the cgroup memory controller. Format: <string> nosocket -- Disable socket memory accounting. nokmem -- Disable kernel memory accounting. nobpf -- Disable BPF memory accounting. checkreqprot= [SELINUX] Set initial checkreqprot flag value. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- check protection applied by kernel (includes any implied execute protection). 1 -- check protection requested by application. Default value is set via a kernel config option. Value can be changed at runtime via /sys/fs/selinux/checkreqprot. Setting checkreqprot to 1 is deprecated. cio_ignore= [S390] See Documentation/s390/common_io.rst for details. clearcpuid=X[,X...] [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeatures.h for the valid bit numbers X. Note the Linux-specific bits are not necessarily stable over kernel options, but the vendor-specific ones should be. X can also be a string as appearing in the flags: line in /proc/cpuinfo which does not have the above instability issue. However, not all features have names in /proc/cpuinfo. Note that using this option will taint your kernel. Also note that user programs calling CPUID directly or using the feature without checking anything will still see it. This just prevents it from being used by the kernel or shown in /proc/cpuinfo. Also note the kernel might malfunction if you disable some critical bits. clk_ignore_unused [CLK] Prevents the clock framework from automatically gating clocks that have not been explicitly enabled by a Linux device driver but are enabled in hardware at reset or by the bootloader/firmware. Note that this does not force such clocks to be always-on nor does it reserve those clocks in any way. This parameter is useful for debug and development, but should not be needed on a platform with proper driver support. For more information, see Documentation/driver-api/clk.rst. clock= [BUGS=X86-32, HW] gettimeofday clocksource override. [Deprecated] Forces specified clocksource (if available) to be used when calculating gettimeofday(). If specified clocksource is not available, it defaults to PIT. Format: { pit | tsc | cyclone | pmtmr } clocksource= Override the default clocksource Format: <string> Override the default clocksource and use the clocksource with the name specified. Some clocksource names to choose from, depending on the platform: [all] jiffies (this is the base, fallback clocksource) [ACPI] acpi_pm [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, pxa_timer,timer3,32k_counter,timer0_1 [X86-32] pit,hpet,tsc; scx200_hrt on Geode; cyclone on IBM x440 [MIPS] MIPS [PARISC] cr16 [S390] tod [SH] SuperH [SPARC64] tick [X86-64] hpet,tsc clocksource.arm_arch_timer.evtstrm= [ARM,ARM64] Format: <bool> Enable/disable the eventstream feature of the ARM architected timer so that code using WFE-based polling loops can be debugged more effectively on production systems. clocksource.max_cswd_read_retries= [KNL] Number of clocksource_watchdog() retries due to external delays before the clock will be marked unstable. Defaults to two retries, that is, three attempts to read the clock under test. clocksource.verify_n_cpus= [KNL] Limit the number of CPUs checked for clocksources marked with CLOCK_SOURCE_VERIFY_PERCPU that are marked unstable due to excessive skew. A negative value says to check all CPUs, while zero says not to check any. Values larger than nr_cpu_ids are silently truncated to nr_cpu_ids. The actual CPUs are chosen randomly, with no replacement if the same CPU is chosen twice. clocksource-wdtest.holdoff= [KNL] Set the time in seconds that the clocksource watchdog test waits before commencing its tests. Defaults to zero when built as a module and to 10 seconds when built into the kernel. cma=nn[MG]@[start[MG][-end[MG]]] [KNL,CMA] Sets the size of kernel global memory area for contiguous memory allocations and optionally the placement constraint by the physical address range of memory allocations. A value of 0 disables CMA altogether. For more information, see kernel/dma/contiguous.c cma_pernuma=nn[MG] [ARM64,KNL,CMA] Sets the size of kernel per-numa memory area for contiguous memory allocations. A value of 0 disables per-numa CMA altogether. And If this option is not specified, the default value is 0. With per-numa CMA enabled, DMA users on node nid will first try to allocate buffer from the pernuma area which is located in node nid, if the allocation fails, they will fallback to the global default memory area. cmo_free_hint= [PPC] Format: { yes | no } Specify whether pages are marked as being inactive when they are freed. This is used in CMO environments to determine OS memory pressure for page stealing by a hypervisor. Default: yes coherent_pool=nn[KMG] [ARM,KNL] Sets the size of memory pool for coherent, atomic dma allocations, by default set to 256K. com20020= [HW,NET] ARCnet - COM20020 chipset Format: <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) Format: <io>[,<irq>] com90xx= [HW,NET] ARCnet - COM90xx chipset (memory-mapped buffers) Format: <io>[,<irq>[,<memstart>]] condev= [HW,S390] console device conmode= con3215_drop= [S390] 3215 console drop mode. Format: y|n|Y|N|1|0 When set to true, drop data on the 3215 console when the console buffer is full. In this case the operator using a 3270 terminal emulator (for example x3270) does not have to enter the clear key for the console output to advance and the kernel to continue. This leads to a much faster boot time when a 3270 terminal emulator is active. If no 3270 terminal emulator is used, this parameter has no effect. console= [KNL] Output console device and options. tty<n> Use the virtual console device <n>. ttyS<n>[,options] ttyUSB0[,options] Use the specified serial port. The options are of the form "bbbbpnf", where "bbbb" is the baud rate, "p" is parity ("n", "o", or "e"), "n" is number of bits, and "f" is flow control ("r" for RTS or omit it). Default is "9600n8". See Documentation/admin-guide/serial-console.rst for more information. See Documentation/networking/netconsole.rst for an alternative. uart[8250],io,<addr>[,options] uart[8250],mmio,<addr>[,options] uart[8250],mmio16,<addr>[,options] uart[8250],mmio32,<addr>[,options] uart[8250],0x<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address, switching to the matching ttyS device later. MMIO inter-register address stride is either 8-bit (mmio), 16-bit (mmio16), or 32-bit (mmio32). If none of [io|mmio|mmio16|mmio32], <addr> is assumed to be equivalent to 'mmio'. 'options' are specified in the same format described for ttyS above; if unspecified, the h/w is not re-initialized. hvc<n> Use the hypervisor console device <n>. This is for both Xen and PowerPC hypervisors. { null | "" } Use to disable console output, i.e., to have kernel console messages discarded. This must be the only console= parameter used on the kernel command line. If the device connected to the port is not a TTY but a braille device, prepend "brl," before the device type, for instance console=brl,ttyS0 For now, only VisioBraille is supported. console_msg_format= [KNL] Change console messages format default By default we print messages on consoles in "[time stamp] text\n" format (time stamp may not be printed, depending on CONFIG_PRINTK_TIME or `printk_time' param). syslog Switch to syslog format: "<%u>[time stamp] text\n" IOW, each message will have a facility and loglevel prefix. The format is similar to one used by syslog() syscall, or to executing "dmesg -S --raw" or to reading from /proc/kmsg. consoleblank= [KNL] The console blank (screen saver) timeout in seconds. A value of 0 disables the blank timer. Defaults to 0. coredump_filter= [KNL] Change the default value for /proc/<pid>/coredump_filter. See also Documentation/filesystems/proc.rst. coresight_cpu_debug.enable [ARM,ARM64] Format: <bool> Enable/disable the CPU sampling based debugging. 0: default value, disable debugging 1: enable debugging at boot time cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver Format: <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] cpu0_hotplug [X86] Turn on CPU0 hotplug feature when CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. Some features depend on CPU0. Known dependencies are: 1. Resume from suspend/hibernate depends on CPU0. Suspend/hibernate will fail if CPU0 is offline and you need to online CPU0 before suspend/hibernate. 2. PIC interrupts also depend on CPU0. CPU0 can't be removed if a PIC interrupt is detected. It's said poweroff/reboot may depend on CPU0 on some machines although I haven't seen such issues so far after CPU0 is offline on a few tested machines. If the dependencies are under your control, you can turn on cpu0_hotplug. [CPU_IDLE] disable the cpuidle sub-system cpuidle.governor= [CPU_IDLE] Name of the cpuidle governor to use. [CPU_FREQ] disable the cpufreq sub-system cpufreq.default_governor= [CPU_FREQ] Name of the default cpufreq governor or policy to use. This governor must be registered in the kernel before the cpufreq driver probes. cpu_init_udelay=N [X86] Delay for N microsec between assert and de-assert of APIC INIT to start processors. This delay occurs on every CPU online, such as boot, and resume from suspend. Default: 10000 crash_kexec_post_notifiers Run kdump after running panic-notifiers and dumping kmsg. This only for the users who doubt kdump always succeeds in any situation. Note that this also increases risks of kdump failure, because some panic notifiers can make the crashed kernel more unstable. crashkernel=size[KMG][@offset[KMG]] [KNL] Using kexec, Linux can switch to a 'crash kernel' upon panic. This parameter reserves the physical memory region [offset, offset + size] for that kernel image. If '@offset' is omitted, then a suitable offset is selected automatically. [KNL, X86-64, ARM64] Select a region under 4G first, and fall back to reserve region above 4G when '@offset' hasn't been specified. See Documentation/admin-guide/kdump/kdump.rst for further details. crashkernel=range1:size1[,range2:size2,...][@offset] [KNL] Same as above, but depends on the memory in the running system. The syntax of range is start-[end] where start and end are both a memory unit (amount[KMG]). See also Documentation/admin-guide/kdump/kdump.rst for an example. crashkernel=size[KMG],high [KNL, X86-64, ARM64] range could be above 4G. Allow kernel to allocate physical memory region from top, so could be above 4G if system have more than 4G ram installed. Otherwise memory region will be allocated below 4G, if available. It will be ignored if crashkernel=X is specified. crashkernel=size[KMG],low [KNL, X86-64, ARM64] range under 4G. When crashkernel=X,high is passed, kernel could allocate physical memory region above 4G, that cause second kernel crash on system that require some amount of low memory, e.g. swiotlb requires at least 64M+32K low memory, also enough extra low memory is needed to make sure DMA buffers for 32-bit devices won't run out. Kernel would try to allocate default size of memory below 4G automatically. The default size is platform dependent. --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) --> arm64: 128MiB This one lets the user specify own low range under 4G for second kernel instead. 0: to disable low allocation. It will be ignored when crashkernel=X,high is not used or memory reserved is below 4G. cryptomgr.notests [KNL] Disable crypto self-tests cs89x0_dma= [HW,NET] Format: <dma> cs89x0_media= [HW,NET] Format: { rj45 | aui | bnc } csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call handling. When switched on, additional debug data is printed to the console in case a hanging CPU is detected, and that CPU is pinged again in order to try to resolve the hang situation. 0: disable csdlock debugging (default) 1: enable basic csdlock debugging (minor impact) ext: enable extended csdlock debugging (more impact, but more data) dasd= [HW,NET] See header of drivers/s390/block/dasd_devmap.c.[2|3]= [HW,JOY] Multisystem joystick support via parallel port (one device per port) Format: <port#>,<type> See also Documentation/input/devices/joystick-parport.rst debug [KNL] Enable kernel debugging (events log level). debug_boot_weak_hash [KNL] Enable printing [hashed] pointers early in the boot sequence. If enabled, we use a weak hash instead of siphash to hash pointers. Use this option if you are seeing instances of '(___ptrval___)') and need to see a value (hashed pointer) instead. Cryptographically insecure, please do not use on production kernels. debug_locks_verbose= [KNL] verbose locking self-tests Format: <int> Print debugging info while doing the locking API self-tests. Bitmask for the various LOCKTYPE_ tests. Defaults to 0 (no extra messages), setting it to -1 (all bits set) will print _a_lot_ more information - normally only useful to lockdep developers. debug_objects [KNL] Enable object debugging no_debug_objects [KNL] Disable object debugging debug_guardpage_minorder= [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter allows control of the order of pages that will be intentionally kept free (and hence protected) by the buddy allocator. Bigger value increase the probability of catching random memory corruption, but reduce the amount of memory for normal system use. The maximum possible value is MAX_ORDER/2. Setting this parameter to 1 or 2 should be enough to identify most random memory corruption problems caused by bugs in kernel or driver code when a CPU writes to (or reads from) a random memory location. Note that there exists a class of memory corruptions problems caused by buggy H/W or F/W or by drivers badly programming DMA (basically when memory is written at bus level and the CPU MMU is bypassed) which are not detectable by CONFIG_DEBUG_PAGEALLOC, hence this option will not help tracking down these problems. debug_pagealloc= [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter enables the feature at boot time. By default, it is disabled and the system will work mostly the same as a kernel built without CONFIG_DEBUG_PAGEALLOC. Note: to get most of debug_pagealloc error reports, it's useful to also enable the page_owner functionality. on: enable the feature debugfs= [KNL] This parameter enables what is exposed to userspace and debugfs internal clients. Format: { on, no-mount, off } on: All functions are enabled. no-mount: Filesystem is not registered but kernel clients can access APIs and a crashkernel can be used to read its content. There is nothing to mount. off: Filesystem is not registered and clients get a -EPERM as result when trying to register files or directories within debugfs. This is equivalent of the runtime functionality if debugfs was not enabled in the kernel at all. Default value is set in build-time with a kernel configuration. debugpat [X86] Enable PAT debugging default_hugepagesz= [HW] The size of the default HugeTLB page. This is the size represented by the legacy /proc/ hugepages APIs. In addition, this is the default hugetlb size used for shmget(), mmap() and mounting hugetlbfs filesystems. If not specified, defaults to the architecture's default huge page size. Huge page sizes are architecture dependent. See also Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG] deferred_probe_timeout= [KNL] Debugging option to set a timeout in seconds for deferred probe to give up waiting on dependencies to probe. Only specific dependencies (subsystems or drivers) that have opted in will be ignored. A timeout of 0 will timeout at the end of initcalls. If the time out hasn't expired, it'll be restarted by each successful driver registration. This option will also dump out devices still on the deferred probe list after retrying. delayacct [KNL] Enable per-task delay accounting dell_smm_hwmon.ignore_dmi= [HW] Continue probing hardware even if DMI data indicates that the driver is running on unsupported hardware. dell_smm_hwmon.force= [HW] Activate driver even if SMM BIOS signature does not match list of supported models and enable otherwise blacklisted features. dell_smm_hwmon.power_status= [HW] Report power status in /proc/i8k (disabled by default). dell_smm_hwmon.restricted= [HW] Allow controlling fans only if SYS_ADMIN capability is set. dell_smm_hwmon.fan_mult= [HW] Factor to multiply fan speed with. dell_smm_hwmon.fan_max= [HW] Maximum configurable fan speed. dfltcc= [HW,S390] Format: { on | off | def_only | inf_only | always } on: s390 zlib hardware support for compression on level 1 and decompression (default) off: No s390 zlib hardware support def_only: s390 zlib hardware support for deflate only (compression on level 1) inf_only: s390 zlib hardware support for inflate only (decompression) always: Same as 'on' but ignores the selected compression level always using hardware support (used for debugging) dhash_entries= [KNL] Set number of hash buckets for dentry cache. disable_1tb_segments [PPC] Disables the use of 1TB hash page table segments. This causes the kernel to fall back to 256MB segments which can be useful when debugging issues that require an SLB miss to occur. disable= [IPV6] See Documentation/networking/ipv6.rst. disable_radix [PPC] Disable RADIX MMU mode on POWER9 disable_tlbie [PPC] Disable TLBIE instruction. Currently does not work with KVM, with HASH MMU, or with coherent accelerators. disable_cpu_apicid= [X86,APIC,SMP] Format: <int> The number of initial APIC ID for the corresponding CPU to be disabled at boot, mostly used for the kdump 2nd kernel to disable BSP to wake up multiple CPUs without causing system reset or hang due to sending INIT from AP to BSP. disable_ddw [PPC/PSERIES] Disable Dynamic DMA Window support. Use this to workaround buggy firmware. disable_ipv6= [IPV6] See Documentation/networking/ipv6.rst. disable_mtrr_cleanup [X86] The kernel tries to adjust MTRR layout from continuous to discrete, to make X server driver able to add WB entry later. This parameter disables that. disable_mtrr_trim [X86, Intel and AMD only] By default the kernel will trim any uncacheable memory out of your available memory pool based on MTRR settings. This parameter disables that behavior, possibly causing your machine to run very slowly. disable_timer_pin_1 [X86] Disable PIN 1 of APIC timer Can be useful to work around chipset bugs. dis_ucode_ldr [X86] Disable the microcode loader. dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, this option disables the debugging code at boot. dma_debug_entries=<number> This option allows to tune the number of preallocated entries for DMA-API debugging code. One entry is required per DMA-API allocation. Use this if the DMA-API debugging code disables itself because the architectural default is too low. dma_debug_driver=<driver_name> With this option the DMA-API debugging driver filter feature can be enabled at boot time. Just pass the driver to filter for as the parameter. The filter can be disabled or changed to another driver later using sysfs. driver_async_probe= [KNL] List of driver names to be probed asynchronously. * matches with all driver names. If * is specified, the rest of the listed driver names are those that will NOT match the *. Format: <driver_name1>,<driver_name2>... drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] Broken monitors, graphic adapters, KVMs and EDIDless panels may send no or incorrect EDID data sets. This parameter allows to specify an EDID data sets in the /lib/firmware directory that are used instead. Generic built-in EDID data sets are used, if one of edid/1024x768.bin, edid/1280x1024.bin, edid/1680x1050.bin, or edid/1920x1080.bin is given and no file with the same name exists. Details and instructions how to build your own EDID data are available in Documentation/admin-guide/edid.rst. An EDID data set will only be used for a particular connector, if its name and a colon are prepended to the EDID name. Each connector may use a unique EDID data set by separating the files with a comma. An EDID data set with no connector name will be used for any connectors not explicitly specified. dscc4.setup= [NET] dt_cpu_ftrs= [PPC] Format: {"off" | "known"} Control how the dt_cpu_ftrs device-tree binding is used for CPU feature discovery and setup (if it exists). off: Do not use it, fall back to legacy cpu table. known: Do not pass through unknown features to guests or userspace, only those that the kernel is aware of. dump_apple_properties [X86] Dump name and content of EFI device properties on x86 Macs. Useful for driver authors to determine what data is available or for reverse-engineering. dyndbg[="val"] [KNL,DYNAMIC_DEBUG] <module>.dyndbg[="val"] Enable debug messages at boot time. See Documentation/admin-guide/dynamic-debug-howto.rst for details. early_ioremap_debug [KNL] Enable debug messages in early_ioremap support. This is useful for tracking down temporary early mappings which are not unmapped. earlycon= [KNL] Output early console device and options. When used with no options, the early console is determined by stdout-path property in device tree's chosen node or the ACPI SPCR table if supported by the platform. cdns,<addr>[,options] Start an early, polled-mode console on a Cadence (xuartps) serial port at the specified address. Only supported option is baud rate. If baud rate is not specified, the serial port must already be setup and configured. uart[8250],io,<addr>[,options[,uartclk]] uart[8250],mmio,<addr>[,options[,uartclk]] uart[8250],mmio32,<addr>[,options[,uartclk]] uart[8250],mmio32be,<addr>[,options[,uartclk]] uart[8250],0x<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address. MMIO inter-register address stride is either 8-bit (mmio) or 32-bit (mmio32 or mmio32be). If none of [io|mmio|mmio32|mmio32be], <addr> is assumed to be equivalent to 'mmio'. 'options' are specified in the same format described for "console=ttyS<n>"; if unspecified, the h/w is not initialized. 'uartclk' is the uart clock frequency; if unspecified, it is set to 'BASE_BAUD' * 16. pl011,<addr> pl011,mmio32,<addr> Start an early, polled-mode console on a pl011 serial port at the specified address. The pl011 serial port must already be setup and configured. Options are not yet supported. If 'mmio32' is specified, then only the driver will use only 32-bit accessors to read/write the device registers. liteuart,<addr> Start an early console on a litex serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported. meson,<addr> Start an early, polled-mode console on a meson serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported. msm_serial,<addr> Start an early, polled-mode console on an msm serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported. msm_serial_dm,<addr> Start an early, polled-mode console on an msm serial dm port at the specified address. The serial port must already be setup and configured. Options are not yet supported. owl,<addr> Start an early, polled-mode console on a serial port of an Actions Semi SoC, such as S500 or S900, at the specified address. The serial port must already be setup and configured. Options are not yet supported. rda,<addr> Start an early, polled-mode console on a serial port of an RDA Micro SoC, such as RDA8810PL, at the specified address. The serial port must already be setup and configured. Options are not yet supported. sbi Use RISC-V SBI (Supervisor Binary Interface) for early console. smh Use ARM semihosting calls for early console. s3c2410,<addr> s3c2412,<addr> s3c2440,<addr> s3c6400,<addr> s5pv210,<addr> exynos4210,<addr> Use early console provided by serial driver available on Samsung SoCs, requires selecting proper type and a correct base address of the selected UART port. The serial port must already be setup and configured. Options are not yet supported. lantiq,<addr> Start an early, polled-mode console on a lantiq serial (lqasc) port at the specified address. The serial port must already be setup and configured. Options are not yet supported. lpuart,<addr> lpuart32,<addr> Use early console provided by Freescale LP UART driver found on Freescale Vybrid and QorIQ LS1021A processors. A valid base address must be provided, and the serial port must already be setup and configured. ec_imx21,<addr> ec_imx6q,<addr> Start an early, polled-mode, output-only console on the Freescale i.MX UART at the specified address. The UART must already be setup and configured. ar3700_uart,<addr> Start an early, polled-mode console on the Armada 3700 serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported. qcom_geni,<addr> Start an early, polled-mode console on a Qualcomm Generic Interface (GENI) based serial port at the specified address. The serial port must already be setup and configured. Options are not yet supported. efifb,[options] Start an early, unaccelerated console on the EFI memory mapped framebuffer (if available). On cache coherent non-x86 systems that use system memory for the framebuffer, pass the 'ram' option so that it is mapped with the correct attributes. linflex,<addr> Use early console provided by Freescale LINFlexD UART serial driver for NXP S32V234 SoCs. A valid base address must be provided, and the serial port must already be setup and configured. earlyprintk= [X86,SH,ARM,M68k,S390] earlyprintk=vga earlyprintk=sclp earlyprintk=xen earlyprintk=serial[,ttySn[,baudrate]] earlyprintk=serial[,0x...[,baudrate]] earlyprintk=ttySn[,baudrate] earlyprintk=dbgp[debugController#] earlyprintk=pciserial[,force],bus:device.function[,baudrate] earlyprintk=xdbc[xhciController#] earlyprintk is useful when the kernel crashes before the normal console is initialized. It is not enabled by default because it has some cosmetic problems. Append ",keep" to not disable it when the real console takes over. Only one of vga, serial, or usb debug port can be used at a time. Currently only ttyS0 and ttyS1 may be specified by name. Other I/O ports may be explicitly specified on some architectures (x86 and arm at least) by replacing ttySn with an I/O port address, like this: earlyprintk=serial,0x1008,115200 You can find the port for a given device in /proc/tty/driver/serial: 2: uart:ST16650V2 port:00001008 irq:18 ... Interaction with the standard serial driver is not very good. The VGA output is eventually overwritten by the real console. The xen option can only be used in Xen domains. The sclp output can only be used on s390. The optional "force" to "pciserial" enables use of a PCI device even when its classcode is not of the UART class. edac_report= [HW,EDAC] Control how to report EDAC event Format: {"on" | "off" | "force"} on: enable EDAC to report H/W event. May be overridden by other higher priority error reporting module. off: disable H/W event reporting through EDAC. force: enforce the use of EDAC to report H/W event. default: on. edd= [EDD] Format: {"off" | "on" | "skip[mbr]"} efi= [EFI] Format: { "debug", "disable_early_pci_dma", "nochunk", "noruntime", "nosoftreserve", "novamap", "no_disable_early_pci_dma" } debug: enable misc debug output. disable_early_pci_dma: disable the busmaster bit on all PCI bridges while in the EFI boot stub. nochunk: disable reading files in "chunks" in the EFI boot stub, as chunking can cause problems with some firmware implementations. noruntime : disable EFI runtime services support nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) attribute may cause the kernel to reserve the memory range for a memory mapping driver to claim. Specify efi=nosoftreserve to disable this reservation and treat the memory by its base type (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). novamap: do not call SetVirtualAddressMap(). no_disable_early_pci_dma: Leave the busmaster bit set on all PCI bridges while in the EFI boot stub efi_no_storage_paranoia [EFI; X86] Using this parameter you can use more than 50% of your efi variable storage. Use this parameter only if you are really sure that your UEFI does sane gc and fulfills the spec otherwise your board may brick. efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] Add arbitrary attribute to specific memory range by updating original EFI memory map. Region of memory which aa attribute is added to is from ss to ss+nn. If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) attribute is added to range 0x100000000-0x180000000 and 0x10a0000000-0x1120000000. If efi_fake_mem=8G@9G:0x40000 is specified, the EFI_MEMORY_SP(0x40000) attribute is added to range 0x240000000-0x43fffffff. Using this parameter you can do debugging of EFI memmap related features. For example, you can do debugging of Address Range Mirroring feature even if your box doesn't support it, or mark specific memory as "soft reserved". efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT that is to be dynamically loaded by Linux. If there are multiple variables with the same name but with different vendor GUIDs, all of them will be loaded. See Documentation/admin-guide/acpi/ssdt-overlays.rst for details. eisa_irq_edge= [PARISC,HW] See header of drivers/parisc/eisa.c. ekgdboc= [X86,KGDB] Allow early kernel console debugging Format: ekgdboc=kbd This is designed to be used in conjunction with the boot argument: earlyprintk=vga This parameter works in place of the kgdboc parameter but can only be used if the backing tty is available very early in the boot process. For early debugging via a serial port see kgdboc_earlycon instead. elanfreq= [X86-32] See comment before function elanfreq_setup() in arch/x86/kernel/cpu/cpufreq/elanfreq.c. elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] Specifies physical address of start of kernel core image elf header and optionally the size. Generally kexec loader will pass this option to capture kernel. See Documentation/admin-guide/kdump/kdump.rst for details. enable_mtrr_cleanup [X86] The kernel tries to adjust MTRR layout from continuous to discrete, to make X server driver able to add WB entry later. This parameter enables that. enable_timer_pin_1 [X86] Enable PIN 1 of APIC timer Can be useful to work around chipset bugs (in particular on some ATI chipsets). The kernel tries to set a reasonable default. enforcing= [SELINUX] Set initial enforcing status. Format: {"0" | "1"} See security/selinux/Kconfig help text. 0 -- permissive (log only, no denials). 1 -- enforcing (deny and log). Default value is 0. Value can be changed at runtime via /sys/fs/selinux/enforce. erst_disable [ACPI] Disable Error Record Serialization Table (ERST) support. ether= [HW,NET] Ethernet cards parameters This option is obsoleted by the "netdev=" option, which has equivalent usage. See its documentation for details. evm= [EVM] Format: { "fix" } Permit 'security.evm' to be updated regardless of current integrity status. early_page_ext [KNL] Enforces page_ext initialization to earlier stages so cover more early boot allocations. Please note that as side effect some optimizations might be disabled to achieve that (e.g. parallelized memory initialization is disabled) so the boot process might take longer, especially on systems with a lot of memory. Available with CONFIG_PAGE_EXTENSION=y. failslab= fail_usercopy= fail_page_alloc= fail_make_request=[KNL] General fault injection mechanism. Format: <interval>,<probability>,<space>,<times> See also Documentation/fault-injection/. fb_tunnels= [NET] Format: { initns | none } See Documentation/admin-guide/sysctl/net.rst for fb_tunnels_only_for_init_ns floppy= [HW] See Documentation/admin-guide/blockdev/floppy.rst. force_pal_cache_flush [IA-64] Avoid check_sal_cache_flush which may hang on buggy SAL_CACHE_FLUSH implementations. Using this parameter will force ia64_sal_cache_flush to call ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. forcepae [X86-32] Forcefully enable Physical Address Extension (PAE). Many Pentium M systems disable PAE but may have a functionally usable PAE implementation. Warning: use of this parameter will taint the kernel and may cause unknown problems. ftrace=[tracer] [FTRACE] will set and start the specified tracer as early as possible in order to facilitate early boot debugging. ftrace_boot_snapshot [FTRACE] On boot up, a snapshot will be taken of the ftrace ring buffer that can be read at: /sys/kernel/tracing/snapshot. This is useful if you need tracing information from kernel boot up that is likely to be overridden by user space start up functionality. Optionally, the snapshot can also be defined for a tracing instance that was created by the trace_instance= command line parameter. trace_instance=foo,sched_switch ftrace_boot_snapshot=foo The above will cause the "foo" tracing instance to trigger a snapshot at the end of boot up. ftrace_dump_on_oops[=orig_cpu] [FTRACE] will dump the trace buffers on oops. If no parameter is passed, ftrace will dump buffers of all CPUs, but if you pass orig_cpu, it will dump only the buffer of the CPU that triggered the oops. ftrace_filter=[function-list] [FTRACE] Limit the functions traced by the function tracer at boot up. function-list is a comma-separated list of functions. This list can be changed at run time by the set_ftrace_filter file in the debugfs tracing directory. ftrace_notrace=[function-list] [FTRACE] Do not trace the functions specified in function-list. This list can be changed at run time by the set_ftrace_notrace file in the debugfs tracing directory. ftrace_graph_filter=[function-list] [FTRACE] Limit the top level callers functions traced by the function graph tracer at boot up. function-list is a comma-separated list of functions that can be changed at run time by the set_graph_function file in the debugfs tracing directory. ftrace_graph_notrace=[function-list] [FTRACE] Do not trace from the functions specified in function-list. This list is a comma-separated list of functions that can be changed at run time by the set_graph_notrace file in the debugfs tracing directory. ftrace_graph_max_depth=<uint> [FTRACE] Used with the function graph tracer. This is the max depth it will trace into a function. This value can be changed at run time by the max_graph_depth file in the tracefs tracing directory. default: 0 (no limit) fw_devlink= [KNL] Create device links between consumer and supplier devices by scanning the firmware to infer the consumer/supplier relationships. This feature is especially useful when drivers are loaded as modules as it ensures proper ordering of tasks like device probing (suppliers first, then consumers), supplier boot state clean up (only after all consumers have probed), suspend/resume & runtime PM (consumers first, then suppliers). Format: { off | permissive | on | rpm } off -- Don't create device links from firmware info. permissive -- Create device links from firmware info but use it only for ordering boot state clean up (sync_state() calls). on -- Create device links from firmware info and use it to enforce probe and suspend/resume ordering. rpm -- Like "on", but also use to order runtime PM. fw_devlink.strict=<bool> [KNL] Treat all inferred dependencies as mandatory dependencies. This only applies for fw_devlink=on|rpm. Format: <bool>[2|3]= [HW,JOY] Multisystem joystick and NES/SNES/PSX pad support via parallel port (up to 5 devices per port) Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> See also Documentation/input/devices/joystick-parport.rst gamma= [HW,DRM] gart_fix_e820= [X86-64] disable the fix e820 for K8 GART Format: off | on default: on gcov_persist= [GCOV] When non-zero (default), profiling data for kernel modules is saved and remains accessible via debugfs, even when the module is unloaded/reloaded. When zero, profiling data is discarded and associated debugfs files are removed at module unload time. goldfish [X86] Enable the goldfish android emulator platform. Don't use this when you are not running on the android emulator gpio-mockup.gpio_mockup_ranges [HW] Sets the ranges of gpiochip of for this device. Format: <start1>,<end1>,<start2>,<end2>... gpio-mockup.gpio_mockup_named_lines [HW] Let the driver know GPIO lines should be named. gpt [EFI] Forces disk with valid GPT signature but invalid Protective MBR to be treated as GPT. If the primary GPT is corrupted, it enables the backup/alternate GPT to be used instead. grcan.enable0= [HW] Configuration of physical interface 0. Determines the "Enable 0" bit of the configuration register. Format: 0 | 1 Default: 0 grcan.enable1= [HW] Configuration of physical interface 1. Determines the "Enable 0" bit of the configuration register. Format: 0 | 1 Default: 0 [HW] Select which physical interface to use. Format: 0 | 1 Default: 0 grcan.txsize= [HW] Sets the size of the tx buffer. Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. Default: 1024 grcan.rxsize= [HW] Sets the size of the rx buffer. Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. Default: 1024 hardened_usercopy= [KNL] Under CONFIG_HARDENED_USERCOPY, whether hardening is enabled for this boot. Hardened usercopy checking is used to protect the kernel from reading or writing beyond known memory allocation boundaries as a proactive defense against bounds-checking flaws in the kernel's copy_to_user()/copy_from_user() interface. on Perform hardened usercopy checks (default). off Disable hardened usercopy checks. hardlockup_all_cpu_backtrace= [KNL] Should the hard-lockup detector generate backtraces on all cpus. Format: 0 | 1 hashdist= [KNL,NUMA] Large hashes allocated during boot are distributed across NUMA nodes. Defaults on for 64-bit NUMA, off otherwise. Format: 0 | 1 (for off | on) hcl= [IA-64] SGI's Hardware Graph compatibility layer hd= [EIDE] (E)IDE hard drive subsystem geometry Format: <cyl>,<head>,<sect> hest_disable [ACPI] Disable Hardware Error Source Table (HEST) support; corresponding firmware-first mode error processing logic will be disabled. hibernate= [HIBERNATION] noresume Don't check if there's a hibernation image present during boot. nocompress Don't compress/decompress hibernation images. no Disable hibernation and resume. protect_image Turn on image protection during restoration (that will set all pages holding image data during restoration read-only). highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact size of <nn>. This works even on boxes that have no highmem otherwise. This also works to reduce highmem size on bigger boxes. highres= [KNL] Enable/disable high resolution timer mode. Valid parameters: "on", "off" Default: "on" hlt [BUGS=ARM,SH] hostname= [KNL] Set the hostname (aka UTS nodename). Format: <string> This allows setting the system's hostname during early startup. This sets the name returned by gethostname. Using this parameter to set the hostname makes it possible to ensure the hostname is correctly set before any userspace processes run, avoiding the possibility that a process may call gethostname before the hostname has been explicitly set, resulting in the calling process getting an incorrect result. The string must not exceed the maximum allowed hostname length (usually 64 characters) and will be truncated otherwise. hpet= [X86-32,HPET] option to control HPET usage Format: { enable (default) | disable | force | verbose } disable: disable HPET and use PIT instead force: allow force enabled of undocumented chips (ICH4, VIA, nVidia) verbose: show contents of HPET registers during setup hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET registers. Default set by CONFIG_HPET_MMAP_DEFAULT. hugepages= [HW] Number of HugeTLB pages to allocate at boot. If this follows hugepagesz (below), it specifies the number of pages of hugepagesz to be allocated. If this is the first HugeTLB parameter on the command line, it specifies the number of pages to allocate for the default huge page size. If using node format, the number of pages to allocate per-node can be specified. See also Documentation/admin-guide/mm/hugetlbpage.rst. Format: <integer> or (node format) <node>:<integer>[,<node>:<integer>] hugepagesz= [HW] The size of the HugeTLB pages. This is used in conjunction with hugepages (above) to allocate huge pages of a specific size at boot. The pair hugepagesz=X hugepages=Y can be specified once for each supported huge page size. Huge page sizes are architecture dependent. See also Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG] hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation of gigantic hugepages. Or using node format, the size of a CMA area per node can be specified. Format: nn[KMGTPE] or (node format) <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] Reserve a CMA area of given size and allocate gigantic hugepages using the CMA allocator. If enabled, the boot-time allocation of gigantic hugepages is skipped. hugetlb_free_vmemmap= [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP enabled. Control if HugeTLB Vmemmap Optimization (HVO) is enabled. Allows heavy hugetlb users to free up some more memory (7 * PAGE_SIZE for each 2MB hugetlb page). Format: { on | off (default) } on: enable HVO off: disable HVO Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, the default is on. Note that the vmemmap pages may be allocated from the added memory block itself when memory_hotplug.memmap_on_memory is enabled, those vmemmap pages cannot be optimized even if this feature is enabled. Other vmemmap pages not allocated from the added memory block itself do not be affected. hung_task_panic= [KNL] Should the hung task detector generate panics. Format: 0 | 1 A value of 1 instructs the kernel to panic when a hung task is detected. The default value is controlled by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value selected by this boot parameter can be changed later by the kernel.hung_task_panic sysctl. hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) terminal devices. Valid values: 0..8 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. If specified, z/VM IUCV HVC accepts connections from listed z/VM user IDs only. hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations which allow the hypervisor to 'idle' the guest on lock contention. i2c_bus= [HW] Override the default board specific I2C bus speed or register an additional I2C bus that is not registered from board initialization code. Format: <bus_id>,<clkrate> i8042.debug [HW] Toggle i8042 debug mode i8042.unmask_kbd_data [HW] Enable printing of interrupt data from the KBD port (disabled by default, and as a pre-condition requires that i8042.debug=1 be enabled) [HW] Put keyboard port into non-translated mode i8042.dumbkbd [HW] Pretend that controller can only read data from keyboard and cannot control its state (Don't attempt to blink the leds) i8042.noaux [HW] Don't check for auxiliary (== mouse) port i8042.nokbd [HW] Don't check/create keyboard port i8042.noloop [HW] Disable the AUX Loopback command while probing for the AUX port i8042.nomux [HW] Don't check presence of an active multiplexing controller i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX controllers i8042.notimeout [HW] Ignore timeout condition signalled by controller i8042.reset [HW] Reset the controller during init, cleanup and suspend-to-ram transitions, only during s2r transitions, or never reset Format: { 1 | Y | y | 0 | N | n } 1, Y, y: always reset controller 0, N, n: don't ever reset controller Default: only on s2r transitions on x86; most other architectures force reset to be always executed i8042.unlock [HW] Unlock (ignore) the keylock i8042.kbdreset [HW] Reset device connected to KBD port i8042.probe_defer [HW] Allow deferred probing upon i8042 probe errors i810= [HW,DRM] i915.invert_brightness= [DRM] Invert the sense of the variable that is used to set the brightness of the panel backlight. Normally a brightness value of 0 indicates backlight switched off, and the maximum of the brightness value sets the backlight to maximum brightness. If this parameter is set to 0 (default) and the machine requires it, or this parameter is set to 1, a brightness value of 0 sets the backlight to maximum brightness, and the maximum of the brightness value switches the backlight off. -1 -- never invert brightness 0 -- machine default 1 -- force brightness inversion icn= [HW,ISDN] Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] idle= [X86] Format: idle=poll, idle=halt, idle=nomwait Poll forces a polling idle loop that can slightly improve the performance of waking up a idle CPU, but will use a lot of power and make the system run hot. Not recommended. idle=halt: Halt is forced to be used for CPU idle. In such case C2/C3 won't be used again. idle=nomwait: Disable mwait for CPU C-states idxd.sva= [HW] Format: <bool> Allow force disabling of Shared Virtual Memory (SVA) support for the idxd driver. By default it is set to true (1). idxd.tc_override= [HW] Format: <bool> Allow override of default traffic class configuration for the device. By default it is set to false (0). ieee754= [MIPS] Select IEEE Std 754 conformance mode Format: { strict | legacy | 2008 | relaxed } Default: strict Choose which programs will be accepted for execution based on the IEEE 754 NaN encoding(s) supported by the FPU and the NaN encoding requested with the value of an ELF file header flag individually set by each binary. Hardware implementations are permitted to support either or both of the legacy and the 2008 NaN encoding mode. Available settings are as follows: strict accept binaries that request a NaN encoding supported by the FPU legacy only accept legacy-NaN binaries, if supported by the FPU 2008 only accept 2008-NaN binaries, if supported by the FPU relaxed accept any binaries regardless of whether supported by the FPU The FPU emulator is always able to support both NaN encodings, so if no FPU hardware is present or it has been disabled with 'nofpu', then the settings of 'legacy' and '2008' strap the emulator accordingly, 'relaxed' straps the emulator for both legacy-NaN and 2008-NaN, whereas 'strict' enables legacy-NaN only on legacy processors and both NaN encodings on MIPS32 or MIPS64 CPUs. The setting for ABS.fmt/NEG.fmt instruction execution mode generally follows that for the NaN encoding, except where unsupported by hardware. ignore_loglevel [KNL] Ignore loglevel setting - this will print /all/ kernel messages to the console. Useful for debugging. We also add it as printk module parameter, so users could change it dynamically, usually by /sys/module/printk/parameters/ignore_loglevel. ignore_rlimit_data Ignore RLIMIT_DATA setting for data mappings, print warning at first misuse. Can be changed via /sys/module/kernel/parameters/ignore_rlimit_data. ihash_entries= [KNL] Set number of hash buckets for inode cache. ima_appraise= [IMA] appraise integrity measurements Format: { "off" | "enforce" | "fix" | "log" } default: "enforce" ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. The builtin appraise policy appraises all files owned by uid=0. ima_canonical_fmt [IMA] Use the canonical format for the binary runtime measurements, instead of host native format. ima_hash= [IMA] Format: { md5 | sha1 | rmd160 | sha256 | sha384 | sha512 | ... } default: "sha1" The list of supported hash algorithms is defined in crypto/hash_info.h. ima_policy= [IMA] The builtin policies to load during IMA setup. Format: "tcb | appraise_tcb | secure_boot | fail_securely | critical_data" The "tcb" policy measures all programs exec'd, files mmap'd for exec, and all files opened with the read mode bit set by either the effective uid (euid=0) or uid=0. The "appraise_tcb" policy appraises the integrity of all files owned by root. The "secure_boot" policy appraises the integrity of files (eg. kexec kernel image, kernel modules, firmware, policy, etc) based on file signatures. The "fail_securely" policy forces file signature verification failure also on privileged mounted filesystems with the SB_I_UNVERIFIABLE_SIGNATURE flag. The "critical_data" policy measures kernel integrity critical data. ima_tcb [IMA] Deprecated. Use ima_policy= instead. Load a policy which meets the needs of the Trusted Computing Base. This means IMA will measure all programs exec'd, files mmap'd for exec, and all files opened for read by uid=0. ima_template= [IMA] Select one of defined IMA measurements template formats. Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | "ima-sigv2" } Default: "ima-ng" ima_template_fmt= [IMA] Define a custom template format. Format: { "field1|...|fieldN" } ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage Format: <min_file_size> Set the minimal file size for using asynchronous hash. If left unspecified, ahash usage is disabled. ahash performance varies for different data sizes on different crypto accelerators. This option can be used to achieve the best performance for a particular HW. ima.ahash_bufsize= [IMA] Asynchronous hash buffer size Format: <bufsize> Set hashing buffer size. Default: 4k. ahash performance varies for different chunk sizes on different crypto accelerators. This option can be used to achieve best performance for particular HW. init= [KNL] Format: <full_path> Run specified binary instead of /sbin/init as init process. initcall_debug [KNL] Trace initcalls as they are executed. Useful for working out where the kernel is dying during startup. initcall_blacklist= [KNL] Do not execute a comma-separated list of initcall functions. Useful for debugging built-in modules and initcalls. initramfs_async= [KNL] Format: <bool> Default: 1 This parameter controls whether the initramfs image is unpacked asynchronously, concurrently with devices being probed and initialized. This should normally just work, but as a debugging aid, one can get the historical behaviour of the initramfs unpacking being completed before device_ and late_ initcalls. initrd= [BOOT] Specify the location of the initial ramdisk initrdmem= [KNL] Specify a physical address and size from which to load the initrd. If an initrd is compiled in or specified in the bootparams, it takes priority over this setting. Format: ss[KMG],nn[KMG] Default is 0, 0 init_on_alloc= [MM] Fill newly allocated pages and heap objects with zeroes. Format: 0 | 1 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. init_on_free= [MM] Fill freed pages and heap objects with zeroes. Format: 0 | 1 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. init_pkru= [X86] Specify the default memory protection keys rights register contents for all processes. 0x55555554 by default (disallow access to all but pkey 0). Can override in debugfs after boot. inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver Format: <irq> int_pln_enable [X86] Enable power limit notification interrupt integrity_audit=[IMA] Format: { "0" | "1" } 0 -- basic integrity auditing messages. (Default) 1 -- additional integrity auditing messages. intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option on Enable intel iommu driver. off Disable intel iommu driver. igfx_off [Default Off] By default, gfx is mapped as normal device. If a gfx device has a dedicated DMAR unit, the DMAR unit is bypassed by not enabling DMAR with this option. In this case, gfx device will use physical address for DMA. strict [Default Off] Deprecated, equivalent to iommu.strict=1. sp_off [Default Off] By default, super page will be supported if Intel IOMMU has the capability. With this option, super page will not be supported. sm_on Enable the Intel IOMMU scalable mode if the hardware advertises that it has support for the scalable mode translation. sm_off Disallow use of the Intel IOMMU scalable mode. tboot_noforce [Default Off] Do not force the Intel IOMMU enabled under tboot. By default, tboot will force Intel IOMMU on, which could harm performance of some high-throughput devices like 40GBit network cards, even if identity mapping is enabled. Note that using this option lowers the security provided by tboot because it makes the system vulnerable to DMA attacks. intel_idle.max_cstate= [KNL,HW,ACPI,X86] 0 disables intel_idle and fall back on acpi_idle. 1 to 9 specify maximum depth of C-state. intel_pstate= [X86] disable Do not enable intel_pstate as the default scaling driver for the supported processors passive Use intel_pstate as a scaling driver, but configure it to work with generic cpufreq governors (instead of enabling its internal governor). This mode cannot be used along with the hardware-managed P-states (HWP) feature. force Enable intel_pstate on systems that prohibit it by default in favor of acpi-cpufreq. Forcing the intel_pstate driver instead of acpi-cpufreq may disable platform features, such as thermal controls and power capping, that rely on ACPI P-States information being indicated to OSPM and therefore should be used with caution. This option does not work with processors that aren't supported by the intel_pstate driver or on platforms that use pcc-cpufreq instead of acpi-cpufreq. no_hwp Do not enable hardware P state control (HWP) if available. hwp_only Only load intel_pstate on systems which support hardware P state control (HWP) if available. support_acpi_ppc Enforce ACPI _PPC performance limits. If the Fixed ACPI Description Table, specifies preferred power management profile as "Enterprise Server" or "Performance Server", then this feature is turned on by default. per_cpu_perf_limits Allow per-logical-CPU P-State performance control limits using cpufreq sysfs interface intremap= [X86-64, Intel-IOMMU] on enable Interrupt Remapping (default) off disable Interrupt Remapping nosid disable Source ID checking no_x2apic_optout BIOS x2APIC opt-out request will be ignored nopost disable Interrupt Posting iomem= Disable strict checking of access to MMIO memory strict regions from userspace. relaxed iommu= [X86] off force noforce biomerge panic nopanic merge nomerge soft pt [X86] nopt [X86] nobypass [PPC/POWERNV] Disable IOMMU bypass, using IOMMU for PCI devices. iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. Format: { "0" | "1" } 0 - Try to allocate a 32-bit DMA address first, before falling back to the full range if needed. 1 - Allocate directly from the full usable range, forcing Dual Address Cycle for PCI cards supporting greater than 32-bit addressing. iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour Format: { "0" | "1" } 0 - Lazy mode. Request that DMA unmap operations use deferred invalidation of hardware TLBs, for increased throughput at the cost of reduced device isolation. Will fall back to strict mode if not supported by the relevant IOMMU driver. 1 - Strict mode. DMA unmap operations invalidate IOMMU hardware TLBs synchronously. unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. Note: on x86, strict mode specified via one of the legacy driver-specific options takes precedence. iommu.passthrough= [ARM64, X86] Configure DMA to bypass the IOMMU by default. Format: { "0" | "1" } 0 - Use IOMMU translation for DMA. 1 - Bypass the IOMMU for DMA. unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. io7= [HW] IO7 for Marvel-based Alpha systems See comment before marvel_specify_io7 in arch/alpha/kernel/core_marvel.c. io_delay= [X86] I/O delay method 0x80 Standard port 0x80 based delay 0xed Alternate port 0xed based delay (needed on some systems) udelay Simple two microseconds delay none No delay ip= [IP_PNP] See Documentation/admin-guide/nfs/nfsroot.rst. ipcmni_extend [KNL] Extend the maximum number of unique System V IPC identifiers from 32,768 to 16,777,216. irqaffinity= [SMP] Set the default irq affinity mask The argument is a cpu list, as described above. irqchip.gicv2_force_probe= [ARM, ARM64] Format: <bool> Force the kernel to look for the second 4kB page of a GICv2 controller even if the memory range exposed by the device tree is too small. irqchip.gicv3_nolpi= [ARM, ARM64] Force the kernel to ignore the availability of LPIs (and by consequence ITSs). Intended for system that use the kernel as a bootloader, and thus want to let secondary kernels in charge of setting up LPIs. irqchip.gicv3_pseudo_nmi= [ARM64] Enables support for pseudo-NMIs in the kernel. This requires the kernel to be built with CONFIG_ARM64_PSEUDO_NMI. irqfixup [HW] When an interrupt is not handled search all handlers for it. Intended to get systems with badly broken firmware running. irqpoll [HW] When an interrupt is not handled search all handlers for it. Also check all handlers each timer interrupt. Intended to get systems with badly broken firmware running. isapnp= [ISAPNP] Format: <RDP>,<reset>,<pci_scan>,<verbosity> isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. [Deprecated - use cpusets instead] Format: [flag-list,]<cpu-list> Specify one or more CPUs to isolate from disturbances specified in the flag list (default: domain): nohz Disable the tick when a single task runs. A residual 1Hz tick is offloaded to workqueues, which you need to affine to housekeeping through the global workqueue's affinity configured via the /sys/devices/virtual/workqueue/cpumask sysfs file, or by using the 'domain' flag described below. NOTE: by default the global workqueue runs on all CPUs, so to protect individual CPUs the 'cpumask' file has to be configured manually after bootup. domain Isolate from the general SMP balancing and scheduling algorithms. Note that performing domain isolation this way is irreversible: it's not possible to bring back a CPU to the domains once isolated through isolcpus. It's strongly advised to use cpusets instead to disable scheduler load balancing through the "cpuset.sched_load_balance" file. It offers a much more flexible interface where CPUs can move in and out of an isolated set anytime. You can move a process onto or off an "isolated" CPU via the CPU affinity syscalls or cpuset. <cpu number> begins at 0 and the maximum value is "number of CPUs in system - 1". managed_irq Isolate from being targeted by managed interrupts which have an interrupt mask containing isolated CPUs. The affinity of managed interrupts is handled by the kernel and cannot be changed via the /proc/irq/* interfaces. This isolation is best effort and only effective if the automatically assigned interrupt mask of a device queue contains isolated and housekeeping CPUs. If housekeeping CPUs are online then such interrupts are directed to the housekeeping CPU so that IO submitted on the housekeeping CPU cannot disturb the isolated CPU. If a queue's affinity mask contains only isolated CPUs then this parameter has no effect on the interrupt routing decision, though interrupts are only delivered when tasks running on those isolated CPUs submit IO. IO submitted on housekeeping CPUs has no influence on those queues. The format of <cpu-list> is described above. iucv= [HW,NET] ivrs_ioapic [HW,X86-64] Provide an override to the IOAPIC-ID<->DEVICE-ID mapping provided in the IVRS ACPI table. By default, PCI segment is 0, and can be omitted. For example, to map IOAPIC-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0, write the parameter as: ivrs_ioapic=10@0001:00:14.0 Deprecated formats: * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=00:14.0 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=0001:00:14.0 ivrs_hpet [HW,X86-64] Provide an override to the HPET-ID<->DEVICE-ID mapping provided in the IVRS ACPI table. By default, PCI segment is 0, and can be omitted. For example, to map HPET-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0, write the parameter as: ivrs_hpet=10@0001:00:14.0 Deprecated formats: * To map HPET-ID decimal 0 to PCI device 00:14.0 write the parameter as: ivrs_hpet[0]=00:14.0 * To map HPET-ID decimal 10 to PCI segment 0x1 and PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=0001:00:14.0 ivrs_acpihid [HW,X86-64] Provide an override to the ACPI-HID:UID<->DEVICE-ID mapping provided in the IVRS ACPI table. By default, PCI segment is 0, and can be omitted. For example, to map UART-HID:UID AMD0020:0 to PCI segment 0x1 and PCI device ID 00:14.5, write the parameter as: ivrs_acpihid=AMD0020:0@0001:00:14.5 Deprecated formats: * To map UART-HID:UID AMD0020:0 to PCI segment is 0, PCI device ID 00:14.5, write the parameter as: ivrs_acpihid[00:14.5]=AMD0020:0 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and PCI device ID 00:14.5, write the parameter as: ivrs_acpihid[0001:00:14.5]=AMD0020:0 js= [HW,JOY] Analog joystick See Documentation/input/joydev/joystick.rst. kasan_multi_shot [KNL] Enforce KASAN (Kernel Address Sanitizer) to print report on every invalid memory access. Without this parameter KASAN will print report only for the first invalid access. keep_bootcon [KNL] Do not unregister boot console at start. This is only useful for debugging when something happens in the window between unregistering the boot console and initializing the real console. keepinitrd [HW,ARM] kernelcore= [KNL,X86,IA-64,PPC] Format: nn[KMGTPE] | nn% | "mirror" This parameter specifies the amount of memory usable by the kernel for non-movable allocations. The requested amount is spread evenly throughout all nodes in the system as ZONE_NORMAL. The remaining memory is used for movable memory in its own zone, ZONE_MOVABLE. In the event, a node is too small to have both ZONE_NORMAL and ZONE_MOVABLE, kernelcore memory will take priority and other nodes will have a larger ZONE_MOVABLE. ZONE_MOVABLE is used for the allocation of pages that may be reclaimed or moved by the page migration subsystem. Note that allocations like PTEs-from-HighMem still use the HighMem zone if it exists, and the Normal zone if it does not. It is possible to specify the exact amount of memory in the form of "nn[KMGTPE]", a percentage of total system memory in the form of "nn%", or "mirror". If "mirror" option is specified, mirrored (reliable) memory is used for non-movable allocations and remaining memory is used for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" are exclusive, so you cannot specify multiple forms. kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. Format: <Controller#>[,poll interval] The controller # is the number of the ehci usb debug port as it is probed via PCI. The poll interval is optional and is the number seconds in between each poll cycle to the debug port in case you need the functionality for interrupting the kernel with gdb or control-c on the dbgp connection. When not using this parameter you use sysrq-g to break into the kernel debugger. kgdboc= [KGDB,HW] kgdb over consoles. Requires a tty driver that supports console polling, or a supported polling keyboard driver (non-usb). Serial only format: <serial_device>[,baud] keyboard only format: kbd keyboard and serial format: kbd,<serial_device>[,baud] Optional Kernel mode setting: kms, kbd format: kms,kbd kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] kgdboc_earlycon= [KGDB,HW] If the boot console provides the ability to read characters and can work in polling mode, you can use this parameter to tell kgdb to use it as a backend until the normal console is registered. Intended to be used together with the kgdboc parameter which specifies the normal console to transition to. The name of the early console should be specified as the value of this parameter. Note that the name of the early console might be different than the tty name passed to kgdboc. It's OK to leave the value blank and the first boot console that implements read() will be picked. kgdbwait [KGDB] Stop kernel execution and enter the kernel debugger at the earliest opportunity. kmac= [MIPS] Korina ethernet MAC address. Configure the RouterBoard 532 series on-chip Ethernet adapter MAC address. kmemleak= [KNL] Boot-time kmemleak enable/disable Valid arguments: on, off Default: on Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, the default is off. kprobe_event=[probe-list] [FTRACE] Add kprobe events and enable at boot time. The probe-list is a semicolon delimited list of probe definitions. Each definition is same as kprobe_events interface, but the parameters are comma delimited. For example, to add a kprobe event on vfs_read with arg1 and arg2, add to the command line; kprobe_event=p,vfs_read,$arg1,$arg2 See also Documentation/trace/kprobetrace.rst "Kernel Boot Parameter" section. kpti= [ARM64] Control page table isolation of user and kernel address spaces. Default: enabled on cores which need mitigation. 0: force disabled 1: force enabled kunit.enable= [KUNIT] Enable executing KUnit tests. Requires CONFIG_KUNIT to be set to be fully enabled. The default value can be overridden via KUNIT_DEFAULT_ENABLED. Default is 1 (enabled) kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. Default is 0 (don't ignore, but inject #GP) kvm.eager_page_split= [KVM,X86] Controls whether or not KVM will try to proactively split all huge pages during dirty logging. Eager page splitting reduces interruptions to vCPU execution by eliminating the write-protection faults and MMU lock contention that would otherwise be required to split huge pages lazily. VM workloads that rarely perform writes or that write only to a small region of VM memory may benefit from disabling eager page splitting to allow huge pages to still be used for reads. The behavior of eager page splitting depends on whether KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If disabled, all huge pages in a memslot will be eagerly split when dirty logging is enabled on that memslot. If enabled, eager page splitting will be performed during the KVM_CLEAR_DIRTY ioctl, and only for the pages being cleared. Eager page splitting is only supported when kvm.tdp_mmu=Y. Default is Y (on). kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. Default is false (don't support). kvm.nx_huge_pages= [KVM] Controls the software workaround for the X86_BUG_ITLB_MULTIHIT bug. force : Always deploy workaround. off : Never deploy workaround. auto : Deploy workaround based on the presence of X86_BUG_ITLB_MULTIHIT. Default is 'auto'. If the software workaround is enabled for the host, guests do need not to enable it for nested guests. kvm.nx_huge_pages_recovery_ratio= [KVM] Controls how many 4KiB pages are periodically zapped back to huge pages. 0 disables the recovery, otherwise if the value is N KVM will zap 1/Nth of the 4KiB pages every period (see below). The default is 60. kvm.nx_huge_pages_recovery_period_ms= [KVM] Controls the time period at which KVM zaps 4KiB pages back to huge pages. If the value is a non-zero N, KVM will zap a portion (see ratio above) of the pages every N msecs. If the value is 0 (the default), KVM will pick a period based on the ratio, such that a page is zapped after 1 hour on average. kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. Default is 1 (enabled) kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) for all guests. Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. kvm-arm.mode= [KVM,ARM] Select one of KVM/arm64's modes of operation. none: Forcefully disable KVM. nvhe: Standard nVHE-based mode, without support for protected guests. protected: nVHE-based mode with support for guests whose state is kept private from the host. nested: VHE-based mode with support for nested virtualization. Requires at least ARMv8.3 hardware. Defaults to VHE/nVHE based on hardware support. Setting mode to "protected" will disable kexec and hibernation for the host. "nested" is experimental and should be used with extreme caution. kvm-arm.vgic_v3_group0_trap= [KVM,ARM] Trap guest accesses to GICv3 group-0 system registers kvm-arm.vgic_v3_group1_trap= [KVM,ARM] Trap guest accesses to GICv3 group-1 system registers kvm-arm.vgic_v3_common_trap= [KVM,ARM] Trap guest accesses to GICv3 common system registers kvm-arm.vgic_v4_enable= [KVM,ARM] Allow use of GICv4 for direct injection of LPIs. kvm_cma_resv_ratio=n [PPC] Reserves given percentage from system memory area for contiguous memory allocation for KVM hash pagetable allocation. By default it reserves 5% of total system memory. Format: <integer> Default: 5 kvm-intel.ept= [KVM,Intel] Disable extended page tables (virtualized MMU) support on capable Intel chips. Default is 1 (enabled) kvm-intel.emulate_invalid_guest_state= [KVM,Intel] Disable emulation of invalid guest state. Ignored if kvm-intel.enable_unrestricted_guest=1, as guest state is never invalid for unrestricted guests. This param doesn't apply to nested guests (L2), as KVM never emulates invalid L2 guest state. Default is 1 (enabled) kvm-intel.flexpriority= [KVM,Intel] Disable FlexPriority feature (TPR shadow). Default is 1 (enabled) kvm-intel.nested= [KVM,Intel] Enable VMX nesting (nVMX). Default is 0 (disabled) kvm-intel.unrestricted_guest= [KVM,Intel] Disable unrestricted guest feature (virtualized real and unpaged mode) on capable Intel chips. Default is 1 (enabled) kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault CVE-2018-3620. Valid arguments: never, cond, always always: L1D cache flush on every VMENTER. cond: Flush L1D on VMENTER only when the code between VMEXIT and VMENTER can leak host memory. never: Disables the mitigation Default is cond (do L1 cache flush in specific instances) kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification feature (tagged TLBs) on capable Intel chips. Default is 1 (enabled) l1d_flush= [X86,INTEL] Control mitigation for L1D based snooping vulnerability. Certain CPUs are vulnerable to an exploit against CPU internal buffers which can forward information to a disclosure gadget under certain conditions. In vulnerable processors, the speculatively forwarded data can be used in a cache side channel attack, to access data to which the attacker does not have direct access. This parameter controls the mitigation. The options are: on - enable the interface for the mitigation l1tf= [X86] Control mitigation of the L1TF vulnerability on affected CPUs The kernel PTE inversion protection is unconditionally enabled and cannot be disabled. full Provides all available mitigations for the L1TF vulnerability. Disables SMT and enables all mitigations in the hypervisors, i.e. unconditional L1D flush. SMT control and L1D flush control via the sysfs interface is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled. full,force Same as 'full', but disables SMT and L1D flush runtime control. Implies the 'nosmt=force' command line option. (i.e. sysfs control of SMT is disabled.) flush Leaves SMT enabled and enables the default hypervisor mitigation, i.e. conditional L1D flush. SMT control and L1D flush control via the sysfs interface is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled. flush,nosmt Disables SMT and enables the default hypervisor mitigation. SMT control and L1D flush control via the sysfs interface is still possible after boot. Hypervisors will issue a warning when the first VM is started in a potentially insecure configuration, i.e. SMT enabled or L1D flush disabled. flush,nowarn Same as 'flush', but hypervisors will not warn when a VM is started in a potentially insecure configuration. off Disables hypervisor mitigations and doesn't emit any warnings. It also drops the swap size and available RAM limit restriction on both hypervisor and bare metal. Default is 'flush'. For details see: Documentation/admin-guide/hw-vuln/l1tf.rst l2cr= [PPC] l3cr= [PPC] lapic [X86-32,APIC] Enable the local APIC even if BIOS disabled it. lapic= [X86,APIC] Do not use TSC deadline value for LAPIC timer one-shot implementation. Default back to the programmable timer unit in the LAPIC. Format: notscdeadline lapic_timer_c2_ok [X86,APIC] trust the local apic timer in C2 power state. libata.dma= [LIBATA] DMA control libata.dma=0 Disable all PATA and SATA DMA libata.dma=1 PATA and SATA Disk DMA only libata.dma=2 ATAPI (CDROM) DMA only libata.dma=4 Compact Flash DMA only Combinations also work, so libata.dma=3 enables DMA for disks and CDROMs, but not CFs. libata.ignore_hpa= [LIBATA] Ignore HPA limit libata.ignore_hpa=0 keep BIOS limits (default) libata.ignore_hpa=1 ignore limits, using full disk libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume when set. Format: <int> libata.force= [LIBATA] Force configurations. The format is a comma- separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. PORT and DEVICE are decimal numbers matching port, link or device. Basically, it matches the ATA ID string printed on console by libata. If the whole ID part is omitted, the last PORT and DEVICE values are used. If ID hasn't been specified yet, the configuration applies to all ports, links and devices. If only DEVICE is omitted, the parameter applies to the port and all links and devices behind it. DEVICE number of 0 either selects the first device or the first fan-out link behind PMP device. It does not select the host link. DEVICE number of 15 selects the host link and device attached to it. The VAL specifies the configuration to force. As long as there is no ambiguity, shortcut notation is allowed. For example, both 1.5 and 1.5G would work for 1.5Gbps. The following configurations can be forced. * Cable type: 40c, 80c, short40c, unk, ign or sata. Any ID with matching PORT is used. * SATA link speed limit: 1.5Gbps or 3.0Gbps. * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. udma[/][16,25,33,44,66,100,133] notation is also allowed. * nohrst, nosrst, norst: suppress hard, soft and both resets. * rstonce: only attempt one reset during hot-unplug link recovery. * [no]dbdelay: Enable or disable the extra 200ms delay before debouncing a link PHY and device presence detection. * [no]ncq: Turn on or off NCQ. * [no]ncqtrim: Enable or disable queued DSM TRIM. * [no]ncqati: Enable or disable NCQ trim on ATI chipset. * [no]trim: Enable or disable (unqueued) TRIM. * trim_zero: Indicate that TRIM command zeroes data. * max_trim_128m: Set 128M maximum trim size limit. * [no]dma: Turn on or off DMA transfers. * atapi_dmadir: Enable ATAPI DMADIR bridge support. * atapi_mod16_dma: Enable the use of ATAPI DMA for commands that are not a multiple of 16 bytes. * [no]dmalog: Enable or disable the use of the READ LOG DMA EXT command to access logs. * [no]iddevlog: Enable or disable access to the identify device data log. * [no]logdir: Enable or disable access to the general purpose log directory. * max_sec_128: Set transfer size limit to 128 sectors. * max_sec_1024: Set or clear transfer size limit to 1024 sectors. * max_sec_lba48: Set or clear transfer size limit to 65535 sectors. * [no]lpm: Enable or disable link power management. * [no]setxfer: Indicate if transfer speed mode setting should be skipped. * [no]fua: Disable or enable FUA (Force Unit Access) support for devices supporting this feature. * dump_id: Dump IDENTIFY data. * disable: Disable this device. If there are multiple matching configurations changing the same attribute, the last one is used. load_ramdisk= [RAM] [Deprecated] lockd.nlm_grace_period=P [NFS] Assign grace period. Format: <integer> lockd.nlm_tcpport=N [NFS] Assign TCP port. Format: <integer> lockd.nlm_timeout=T [NFS] Assign timeout value. Format: <integer> lockd.nlm_udpport=M [NFS] Assign UDP port. Format: <integer> lockdown= [SECURITY] { integrity | confidentiality } Enable the kernel lockdown feature. If set to integrity, kernel features that allow userland to modify the running kernel are disabled. If set to confidentiality, kernel features that allow userland to extract confidential information from the kernel are also disabled. locktorture.nreaders_stress= [KNL] Set the number of locking read-acquisition kthreads. Defaults to being automatically set based on the number of online CPUs. locktorture.nwriters_stress= [KNL] Set the number of locking write-acquisition kthreads. locktorture.onoff_holdoff= [KNL] Set time (s) after boot for CPU-hotplug testing. locktorture.onoff_interval= [KNL] Set time (s) between CPU-hotplug operations, or zero to disable CPU-hotplug testing. locktorture.shuffle_interval= [KNL] Set task-shuffle interval (jiffies). Shuffling tasks allows some CPUs to go into dyntick-idle mode during the locktorture test. locktorture.shutdown_secs= [KNL] Set time (s) after boot system shutdown. This is useful for hands-off automated testing. locktorture.stat_interval= [KNL] Time (s) between statistics printk()s. locktorture.stutter= [KNL] Time (s) to stutter testing, for example, specifying five seconds causes the test to run for five seconds, wait for five seconds, and so on. This tests the locking primitive's ability to transition abruptly to and from idle. locktorture.torture_type= [KNL] Specify the locking implementation to test. locktorture.verbose= [KNL] Enable additional printk() statements. logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver Format: <irq> loglevel= All Kernel Messages with a loglevel smaller than the console loglevel will be printed to the console. It can also be changed with klogd or other programs. The loglevels are defined as follows: 0 (KERN_EMERG) system is unusable 1 (KERN_ALERT) action must be taken immediately 2 (KERN_CRIT) critical conditions 3 (KERN_ERR) error conditions 4 (KERN_WARNING) warning conditions 5 (KERN_NOTICE) normal but significant condition 6 (KERN_INFO) informational 7 (KERN_DEBUG) debug-level messages log_buf_len=n[KMG] Sets the size of the printk ring buffer, in bytes. n must be a power of two and greater than the minimal size. The minimal size is defined by LOG_BUF_SHIFT kernel config parameter. There is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter that allows to increase the default size depending on the number of CPUs. See init/Kconfig for more details. logo.nologo [FB] Disables display of the built-in Linux logo. This may be used to provide more screen space for kernel log messages and is useful when debugging kernel boot problems. lp=0 [LP] Specify parallel ports to use, e.g, lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses lp=reset first parallel port). 'lp=0' disables the lp=auto printer driver. 'lp=reset' (which can be specified in addition to the ports) causes attached printers to be reset. Using lp=port1,port2,... specifies the parallel ports to associate lp devices with, starting with lp0. A port specification may be 'none' to skip that lp device, or a parport name such as 'parport0'. Specifying 'lp=auto' instead of a port specification list means that device IDs from each port should be examined, to see if an IEEE 1284-compliant printer is attached; if so, the driver will manage that printer. See also header of drivers/char/lp.c. lpj=n [KNL] Sets loops_per_jiffy to given constant, thus avoiding time-consuming boot-time autodetection (up to 250 ms per CPU). 0 enables autodetection (default). To determine the correct value for your kernel, boot with normal autodetection and see what value is printed. Note that on SMP systems the preset will be applied to all CPUs, which is likely to cause problems if your CPUs need significantly divergent settings. An incorrect value will cause delays in the kernel to be wrong, leading to unpredictable I/O errors and other breakage. Although unlikely, in the extreme case this might damage your hardware. ltpc= [NET] Format: <io>,<irq>,<dma> lsm.debug [SECURITY] Enable LSM initialization debugging output. lsm=lsm1,...,lsmN [SECURITY] Choose order of LSM initialization. This overrides CONFIG_LSM, and the "security=" parameter. machvec= [IA-64] Force the use of a particular machine-vector (machvec) in a generic kernel. Example: machvec=hpzx1 machtype= [Loongson] Share the same kernel image file between different yeeloong laptops. Example: machtype=lemote-yeeloong-2f-7inch max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater than or equal to this physical address is ignored. maxcpus= [SMP] Maximum number of processors that an SMP kernel will bring up during bootup. maxcpus=n : n >= 0 limits the kernel to bring up 'n' processors. Surely after bootup you can bring up the other plugged cpu by executing "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus only takes effect during system bootup. While n=0 is a special case, it is equivalent to "nosmp", which also disables the IO APIC. max_loop= [LOOP] The number of loop block devices that get (loop.max_loop) unconditionally pre-created at init time. The default number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead of statically allocating a predefined number, loop devices can be requested on-demand with the /dev/loop-control interface. mce [X86-32] Machine Check Exception mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst md= [HW] RAID subsystems devices and level See Documentation/admin-guide/md.rst. mdacon= [MDA] Format: <first>,<last> Specifies range of consoles to be captured by the MDA. mds= [X86,INTEL] Control mitigation for the Micro-architectural Data Sampling (MDS) vulnerability. Certain CPUs are vulnerable to an exploit against CPU internal buffers which can forward information to a disclosure gadget under certain conditions. In vulnerable processors, the speculatively forwarded data can be used in a cache side channel attack, to access data to which the attacker does not have direct access. This parameter controls the MDS mitigation. The options are: full - Enable MDS mitigation on vulnerable CPUs full,nosmt - Enable MDS mitigation and disable SMT on vulnerable CPUs off - Unconditionally disable MDS mitigation On TAA-affected machines, mds=off can be prevented by an active TAA mitigation as both vulnerabilities are mitigated with the same mechanism so in order to disable this mitigation, you need to specify tsx_async_abort=off too. Not specifying this option is equivalent to mds=full. For details see: Documentation/admin-guide/hw-vuln/mds.rst mem=nn[KMG] [HEXAGON] Set the memory size. Must be specified, otherwise memory size will be 0. mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory Amount of memory to be used in cases as follows: 1 for test; 2 when the kernel is not able to see the whole system memory; 3 memory that lies after 'mem=' boundary is excluded from the hypervisor, then assigned to KVM guests. 4 to limit the memory available for kdump kernel. [ARC,MICROBLAZE] - the limit applies only to low memory, high memory is not affected. [ARM64] - only limits memory covered by the linear mapping. The NOMAP regions are not affected. [X86] Work as limiting max address. Use together with memmap= to avoid physical address space collisions. Without memmap= PCI devices could be placed at addresses belonging to unused RAM. Note that this only takes effects during boot time since in above case 3, memory may need be hot added after boot if system memory of hypervisor is not sufficient. mem=nn[KMG]@ss[KMG] [ARM,MIPS] - override the memory layout reported by firmware. Define a memory region of size nn[KMG] starting at ss[KMG]. Multiple different regions can be specified with multiple mem= parameters on the command line. mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel memory. memblock=debug [KNL] Enable memblock debug messages. memchunk=nn[KMG] [KNL,SH] Allow user to override the default size for per-device physically contiguous DMA buffers. memhp_default_state=online/offline [KNL] Set the initial state for the memory hotplug onlining policy. If not specified, the default value is set according to the CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config option. See Documentation/admin-guide/mm/memory-hotplug.rst. memmap=exactmap [KNL,X86] Enable setting of an exact E820 memory map, as specified by the user. Such memmap=exactmap lines can be constructed based on BIOS output or other requirements. See the memmap=nn@ss option description. memmap=nn[KMG]@ss[KMG] [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. Region of memory to be used is from ss to ss+nn. If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], which limits max address to nn[KMG]. Multiple different regions can be specified, comma delimited. Example: memmap=100M@2G,100M#3G,1G!1024G memmap=nn[KMG]#ss[KMG] [KNL,ACPI] Mark specific memory as ACPI data. Region of memory to be marked is from ss to ss+nn. memmap=nn[KMG]$ss[KMG] [KNL,ACPI] Mark specific memory as reserved. Region of memory to be reserved is from ss to ss+nn. Example: Exclude memory from 0x18690000-0x1869ffff memmap=64K$0x18690000 or memmap=0x10000$0x18690000 Some bootloaders may need an escape character before '$', like Grub2, otherwise '$' and the following number will be eaten. memmap=nn[KMG]!ss[KMG] [KNL,X86] Mark specific memory as protected. Region of memory to be used, from ss to ss+nn. The memory region may be marked as e820 type 12 (0xc) and is NVDIMM or ADR memory. memmap=<size>%<offset>-<oldtype>+<newtype> [KNL,ACPI] Convert memory within the specified region from <oldtype> to <newtype>. If "-<oldtype>" is left out, the whole region will be marked as <newtype>, even if previously unavailable. If "+<newtype>" is left out, matching memory will be removed. Types are specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3 = ACPI, 12 = PRAM. memory_corruption_check=0/1 [X86] Some BIOSes seem to corrupt the first 64k of memory when doing things like suspend/resume. Setting this option will scan the memory looking for corruption. Enabling this will both detect corruption and prevent the kernel from using the memory being corrupted. However, its intended as a diagnostic tool; if repeatable BIOS-originated corruption always affects the same memory, you can use memmap= to prevent the kernel from using that memory. memory_corruption_check_size=size [X86] By default it checks for corruption in the low 64k, making this memory unavailable for normal use. Use this parameter to scan for corruption in more or less memory. memory_corruption_check_period=seconds [X86] By default it checks for corruption every 60 seconds. Use this parameter to check at some other rate. 0 disables periodic checking. memory_hotplug.memmap_on_memory [KNL,X86,ARM] Boolean flag to enable this feature. Format: {on | off (default)} When enabled, runtime hotplugged memory will allocate its internal metadata (struct pages, those vmemmap pages cannot be optimized even if hugetlb_free_vmemmap is enabled) from the hotadded memory which will allow to hotadd a lot of memory without requiring additional memory to do so. This feature is disabled by default because it has some implication on large (e.g. GB) allocations in some configurations (e.g. small memory blocks). The state of the flag can be read in /sys/module/memory_hotplug/parameters/memmap_on_memory. Note that even when enabled, there are a few cases where the feature is not effective. memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest Format: <integer> default : 0 <disable> Specifies the number of memtest passes to be performed. Each pass selects another test pattern from a given set of patterns. Memtest fills the memory with this pattern, validates memory contents and reserves bad memory regions that are detected. mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control Valid arguments: on, off Default (depends on kernel configuration option): on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) mem_encrypt=on: Activate SME mem_encrypt=off: Do not activate SME Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst for details on when memory encryption can be activated. mem_sleep_default= [SUSPEND] Default system suspend mode: s2idle - Suspend-To-Idle shallow - Power-On Suspend or equivalent (if supported) deep - Suspend-To-RAM or equivalent (if supported) See Documentation/admin-guide/pm/sleep-states.rst. meye.*= [HW] Set MotionEye Camera parameters See Documentation/admin-guide/media/meye.rst. mfgpt_irq= [IA-32] Specify the IRQ to use for the Multi-Function General Purpose Timers on AMD Geode platforms. mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when the BIOS has incorrectly applied a workaround. TinyBIOS version 0.98 is known to be affected, 0.99 fixes the problem by letting the user disable the workaround. mga= [HW,DRM] min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this physical address is ignored. mini2440= [ARM,HW,KNL] Format:[0..2][b][c][t] Default: "0tb" MINI2440 configuration specification: 0 - The attached screen is the 3.5" TFT 1 - The attached screen is the 7" TFT 2 - The VGA Shield is attached (1024x768) Leaving out the screen size parameter will not load the TFT driver, and the framebuffer will be left unconfigured. b - Enable backlight. The TFT backlight pin will be linked to the kernel VESA blanking code and a GPIO LED. This parameter is not necessary when using the VGA shield. c - Enable the s3c camera interface. t - Reserved for enabling touchscreen support. The touchscreen support is not enabled in the mainstream kernel as of 2.6.30, a preliminary port can be found in the "bleeding edge" mini2440 support kernel at mitigations= [X86,PPC,S390,ARM64] Control optional mitigations for CPU vulnerabilities. This is a set of curated, arch-independent options, each of which is an aggregation of existing arch-specific options. off Disable all optional CPU mitigations. This improves system performance, but it may also expose users to several CPU vulnerabilities. Equivalent to: nopti [X86,PPC] if nokaslr then kpti=0 [ARM64] nospectre_v1 [X86,PPC] nobp=0 [S390] nospectre_v2 [X86,PPC,S390,ARM64] spectre_v2_user=off [X86] spec_store_bypass_disable=off [X86,PPC] ssbd=force-off [ARM64] nospectre_bhb [ARM64] l1tf=off [X86] mds=off [X86] tsx_async_abort=off [X86] kvm.nx_huge_pages=off [X86] srbds=off [X86,INTEL] no_entry_flush [PPC] no_uaccess_flush [PPC] mmio_stale_data=off [X86] retbleed=off [X86] Exceptions: This does not have any effect on kvm.nx_huge_pages when kvm.nx_huge_pages=force. auto (default) Mitigate all CPU vulnerabilities, but leave SMT enabled, even if it's vulnerable. This is for users who don't want to be surprised by SMT getting disabled across kernel upgrades, or who have other ways of avoiding SMT-based attacks. Equivalent to: (default behavior) auto,nosmt Mitigate all CPU vulnerabilities, disabling SMT if needed. This is for users who always want to be fully mitigated, even if it means losing SMT. Equivalent to: l1tf=flush,nosmt [X86] mds=full,nosmt [X86] tsx_async_abort=full,nosmt [X86] mmio_stale_data=full,nosmt [X86] retbleed=auto,nosmt [X86] mminit_loglevel= [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this parameter allows control of the logging verbosity for the additional memory initialisation checks. A value of 0 disables mminit logging and a level of 4 will log everything. Information is printed at KERN_DEBUG so loglevel=8 may also need to be specified. mmio_stale_data= [X86,INTEL] Control mitigation for the Processor MMIO Stale Data vulnerabilities. Processor MMIO Stale Data is a class of vulnerabilities that may expose data after an MMIO operation. Exposed data could originate or end in the same CPU buffers as affected by MDS and TAA. Therefore, similar to MDS and TAA, the mitigation is to clear the affected CPU buffers. This parameter controls the mitigation. The options are: full - Enable mitigation on vulnerable CPUs full,nosmt - Enable mitigation and disable SMT on vulnerable CPUs. off - Unconditionally disable mitigation On MDS or TAA affected machines, mmio_stale_data=off can be prevented by an active MDS or TAA mitigation as these vulnerabilities are mitigated with the same mechanism so in order to disable this mitigation, you need to specify mds=off and tsx_async_abort=off too. Not specifying this option is equivalent to mmio_stale_data=full. For details see: Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst <module>.async_probe[=<bool>] [KNL] If no <bool> value is specified or if the value specified is not a valid <bool>, enable asynchronous probe on this module. Otherwise, enable/disable asynchronous probe on this module as indicated by the <bool> value. See also: module.async_probe module.async_probe=<bool> [KNL] When set to true, modules will use async probing by default. To enable/disable async probing for a specific module, use the module specific control that is documented under <module>.async_probe. When both module.async_probe and <module>.async_probe are specified, <module>.async_probe takes precedence for the specific module. module.sig_enforce [KNL] When CONFIG_MODULE_SIG is set, this means that modules without (valid) signatures will fail to load. Note that if CONFIG_MODULE_SIG_FORCE is set, that is always true, so this option does nothing. module_blacklist= [KNL] Do not load a comma-separated list of modules. Useful for debugging problem modules. mousedev.tap_time= [MOUSE] Maximum time between finger touching and leaving touchpad surface for touch to be considered a tap and be reported as a left button click (for touchpads working in absolute mode only). Format: <msecs> mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices reporting absolute coordinates, such as tablets mousedev.yres= [MOUSE] Vertical screen resolution, used for devices reporting absolute coordinates, such as tablets movablecore= [KNL,X86,IA-64,PPC] Format: nn[KMGTPE] | nn% This parameter is the complement to kernelcore=, it specifies the amount of memory used for migratable allocations. If both kernelcore and movablecore is specified, then kernelcore will be at *least* the specified value but may be more. If movablecore on its own is specified, the administrator must be careful that the amount of memory usable for all allocations is not too small. movable_node [KNL] Boot-time switch to make hotplugable memory NUMA nodes to be movable. This means that the memory of such nodes will be usable only for movable allocations which rules out almost all kernel allocations. Use with caution! MTD_Partition= [MTD] Format: <name>,<region-number>,<size>,<offset> MTD_Region= [MTD] Format: <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] mtdparts= [MTD] See drivers/mtd/parsers/cmdlinepart.c mtdset= [ARM] ARM/S3C2412 JIVE boot control See arch/arm/mach-s3c/mach-jive.c mtouchusb.raw_coordinates= [HW] Make the MicroTouch USB driver use raw coordinates ('y', default) or cooked coordinates ('n') mtrr_chunk_size=nn[KMG] [X86] used for mtrr cleanup. It is largest continuous chunk that could hold holes aka. UC entries. mtrr_gran_size=nn[KMG] [X86] Used for mtrr cleanup. It is granularity of mtrr block. Default is 1. Large value could prevent small alignment from using up MTRRs. mtrr_spare_reg_nr=n [X86] Format: <integer> Range: 0,7 : spare reg number Default : 1 Used for mtrr cleanup. It is spare mtrr entries number. Set to 2 or more if your graphical card needs more. multitce=off [PPC] This parameter disables the use of the pSeries firmware feature for updating multiple TCE entries at a time. n2= [NET] SDL Inc. RISCom/N2 synchronous serial card netdev= [NET] Network devices parameters Format: <irq>,<io>,<mem_start>,<mem_end>,<name> Note that mem_start is often overloaded to mean something different and driver-specific. This usage is only documented in each driver source file if at all. netpoll.carrier_timeout= [NET] Specifies amount of time (in seconds) that netpoll should wait for a carrier. By default netpoll waits 4 seconds. nf_conntrack.acct= [NETFILTER] Enable connection tracking flow accounting 0 to disable accounting 1 to enable accounting Default value is 0. nfsaddrs= [NFS] Deprecated. Use ip= instead. See Documentation/admin-guide/nfs/nfsroot.rst. nfsroot= [NFS] nfs root filesystem for disk-less boxes. See Documentation/admin-guide/nfs/nfsroot.rst. nfsrootdebug [NFS] enable nfsroot debugging messages. See Documentation/admin-guide/nfs/nfsroot.rst. nfs.callback_nr_threads= [NFSv4] set the total number of threads that the NFS client will assign to service NFSv4 callback requests. nfs.callback_tcpport= [NFS] set the TCP port on which the NFSv4 callback channel should listen. nfs.cache_getent= [NFS] sets the pathname to the program which is used to update the NFS client cache entries. nfs.cache_getent_timeout= [NFS] sets the timeout after which an attempt to update a cache entry is deemed to have failed. nfs.idmap_cache_timeout= [NFS] set the maximum lifetime for idmapper cache entries. nfs.enable_ino64= [NFS] enable 64-bit inode numbers. If zero, the NFS client will fake up a 32-bit inode number for the readdir() and stat() syscalls instead of returning the full 64-bit number. The default is to return 64-bit inode numbers. nfs.max_session_cb_slots= [NFSv4.1] Sets the maximum number of session slots the client will assign to the callback channel. This determines the maximum number of callbacks the client will process in parallel for a particular server. nfs.max_session_slots= [NFSv4.1] Sets the maximum number of session slots the client will attempt to negotiate with the server. This limits the number of simultaneous RPC requests that the client can send to the NFSv4.1 server. Note that there is little point in setting this value higher than the max_tcp_slot_table_limit. nfs.nfs4_disable_idmapping= [NFSv4] When set to the default of '1', this option ensures that both the RPC level authentication scheme and the NFS level operations agree to use numeric uids/gids if the mount is using the 'sec=sys' security flavour. In effect it is disabling idmapping, which can make migration from legacy NFSv2/v3 systems to NFSv4 easier. Servers that do not support this mode of operation will be autodetected by the client, and it will fall back to using the idmapper. To turn off this behaviour, set the value to '0'. nfs.nfs4_unique_id= [NFS4] Specify an additional fixed unique ident- ification string that NFSv4 clients can insert into their nfs_client_id4 string. This is typically a UUID that is generated at system install time. nfs.send_implementation_id = [NFSv4.1] Send client implementation identification information in exchange_id requests. If zero, no implementation identification information will be sent. The default is to send the implementation identification information. nfs.recover_lost_locks = [NFSv4] Attempt to recover locks that were lost due to a lease timeout on the server. Please note that doing this risks data corruption, since there are no guarantees that the file will remain unchanged after the locks are lost. If you want to enable the kernel legacy behaviour of attempting to recover these locks, then set this parameter to '1'. The default parameter value of '0' causes the kernel not to attempt recovery of lost locks. nfs4.layoutstats_timer = [NFSv4.2] Change the rate at which the kernel sends layoutstats to the pNFS metadata server. Setting this to value to 0 causes the kernel to use whatever value is the default set by the layout driver. A non-zero value sets the minimum interval in seconds between layoutstats transmissions. nfsd.inter_copy_offload_enable = [NFSv4.2] When set to 1, the server will support server-to-server copies for which this server is the destination of the copy. nfsd.nfsd4_ssc_umount_timeout = [NFSv4.2] When used as the destination of a server-to-server copy, knfsd temporarily mounts the source server. It caches the mount in case it will be needed again, and discards it if not used for the number of milliseconds specified by this parameter. nfsd.nfs4_disable_idmapping= [NFSv4] When set to the default of '1', the NFSv4 server will return only numeric uids and gids to clients using auth_sys, and will accept numeric uids and gids from such clients. This is intended to ease migration from NFSv2/v3. nmi_backtrace.backtrace_idle [KNL] Dump stacks even of idle CPUs in response to an NMI stack-backtrace request. nmi_debug= [KNL,SH] Specify one or more actions to take when a NMI is triggered. Format: [state][,regs][,debounce][,die] nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels Format: [panic,][nopanic,][num] Valid num: 0 or 1 0 - turn hardlockup detector in nmi_watchdog off 1 - turn hardlockup detector in nmi_watchdog on When panic is specified, panic when an NMI watchdog timeout occurs (or 'nopanic' to not panic on an NMI watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) To disable both hard and soft lockup detectors, please see 'nowatchdog'. This is useful when you use a panic=... timeout and need the box quickly up again. These settings can be accessed at runtime via the nmi_watchdog and hardlockup_panic sysctls. no387 [BUGS=X86-32] Tells the kernel to use the 387 maths emulation library even if a 387 maths coprocessor is present. no5lvl [X86-64] Disable 5-level paging mode. Forces kernel to use 4-level paging instead. nofsgsbase [X86] Disables FSGSBASE instructions. no_console_suspend [HW] Never suspend the console Disable suspending of consoles during suspend and hibernate operations. Once disabled, debugging messages can reach various consoles while the rest of the system is being put to sleep (ie, while debugging driver suspend/resume hooks). This may not work reliably with all consoles, but is known to work with serial and VGA consoles. To facilitate more flexible debugging, we also add console_suspend, a printk module parameter to control it. Users could use console_suspend (usually /sys/module/printk/parameters/console_suspend) to turn on/off it dynamically. novmcoredd [KNL,KDUMP] Disable device dump. Device dump allows drivers to append dump data to vmcore so you can collect driver specified debug info. Drivers can append the data without any limit and this data is stored in memory, so this may cause significant memory stress. Disabling device dump can help save memory but the driver debug data will be no longer available. This parameter is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP is set. noaliencache [MM, NUMA, SLAB] Disables the allocation of alien caches in the slab allocator. Saves per-node memory, but will impact performance. noalign [KNL,ARM] noaltinstr [S390] Disables alternative instructions patching (CPU alternatives feature). noapic [SMP,APIC] Tells the kernel to not make use of any IOAPICs that may be present in the system. noautogroup Disable scheduler automatic task group creation. nocache [ARM] nodsp [SH] Disable hardware DSP at boot time. noefi Disable EFI runtime services support. no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. noexec [IA-64] nosmap [PPC] Disable SMAP (Supervisor Mode Access Prevention) even if it is supported by processor. nosmep [PPC64s] Disable SMEP (Supervisor Mode Execution Prevention) even if it is supported by processor. noexec32 [X86-64] This affects only 32-bit executables. noexec32=on: enable non-executable mappings (default) read doesn't imply executable mappings noexec32=off: disable non-executable mappings read implies executable mappings nofpu [MIPS,SH] Disable hardware FPU at boot time. nofxsr [BUGS=X86-32] Disables x86 floating point extended register save and restore. The kernel will only save legacy floating-point registers on task switch. nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings. nosmt [KNL,S390] Disable symmetric multithreading (SMT). Equivalent to smt=1. [KNL,X86] Disable symmetric multithreading (SMT). nosmt=force: Force disable SMT, cannot be undone via the sysfs control file. nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 (bounds check bypass). With this option data leaks are possible in the system. nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for the Spectre variant 2 (indirect branch prediction) vulnerability. System may allow data leaks with this option. nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch history injection) vulnerability. System may allow data leaks with this option. nospec_store_bypass_disable [HW] Disable all mitigations for the Speculative Store Bypass vulnerability no_uaccess_flush [PPC] Don't flush the L1-D cache after accessing user data. noxsave [BUGS=X86] Disables x86 extended register state save and restore using xsave. The kernel will fallback to enabling legacy floating-point and sse state. noxsaveopt [X86] Disables xsaveopt used in saving x86 extended register states. The kernel will fall back to use xsave to save the states. By using this parameter, performance of saving the states is degraded because xsave doesn't support modified optimization while xsaveopt supports it on xsaveopt enabled systems. noxsaves [X86] Disables xsaves and xrstors used in saving and restoring x86 extended register state in compacted form of xsave area. The kernel will fall back to use xsaveopt and xrstor to save and restore the states in standard form of xsave area. By using this parameter, xsave area per process might occupy more memory on xsaves enabled systems. nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait in do_idle() and not use the arch_cpu_idle() implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP to be effective. This is useful on platforms where the sleep(SH) or wfi(ARM,ARM64) instructions do not work correctly or when doing power measurements to evaluate the impact of the sleep instructions. This is also useful when using JTAG debugger. no_file_caps Tells the kernel not to honor file capabilities. The only way then for a file to be executed with privilege is to be setuid root or executed by root. nohalt [IA-64] Tells the kernel not to use the power saving function PAL_HALT_LIGHT when idle. This increases power-consumption. On the positive side, it reduces interrupt wake-up latency, which may improve performance in certain environments such as networked servers or real-time systems. no_hash_pointers Force pointers printed to the console or buffers to be unhashed. By default, when a pointer is printed via %p format string, that pointer is "hashed", i.e. obscured by hashing the pointer value. This is a security feature that hides actual kernel addresses from unprivileged users, but it also makes debugging the kernel more difficult since unequal pointers can no longer be compared. However, if this command-line option is specified, then all normal pointers will have their true value printed. This option should only be specified when debugging the kernel. Please do not use on production kernels. nohibernate [HIBERNATION] Disable hibernation and resume. nohz= [KNL] Boottime enable/disable dynamic ticks Valid arguments: on, off Default: on nohz_full= [KNL,BOOT,SMP,ISOL] The argument is a cpu list, as described above. In kernels built with CONFIG_NO_HZ_FULL=y, set the specified list of CPUs whose tick will be stopped whenever possible. The boot CPU will be forced outside the range to maintain the timekeeping. Any CPUs in this list will have their RCU callbacks offloaded, just as if they had also been called out in the rcu_nocbs= boot parameter. Note that this argument takes precedence over the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. noiotrap [SH] Disables trapped I/O port accesses. noirqdebug [X86-32] Disables the code which attempts to detect and disable unhandled interrupt sources. no_timer_check [X86,APIC] Disables the code which tests for broken timer IRQ sources. noisapnp [ISAPNP] Disables ISA PnP code. noinitrd [RAM] Tells the kernel not to load any configured initial RAM disk. nointremap [X86-64, Intel-IOMMU] Do not enable interrupt remapping. [Deprecated - use intremap=off] nointroute [IA-64] noinvpcid [X86] Disable the INVPCID cpu feature. nojitter [IA-64] Disables jitter checking for ITC timers. nokaslr [KNL] When CONFIG_RANDOMIZE_BASE is set, this disables kernel and module base offset ASLR (Address Space Layout Randomization). no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page fault handling. no-vmw-sched-clock [X86,PV_OPS] Disable paravirtualized VMware scheduler clock and use the default one. no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES] Disable paravirtualized steal time accounting. steal time is computed, but won't influence scheduler behaviour nolapic [X86-32,APIC] Do not enable or use the local APIC. nolapic_timer [X86-32,APIC] Do not use the local APIC timer. nomca [IA-64] Disable machine check abort handling nomce [X86-32] Disable Machine Check Exception nomfgpt [X86-32] Disable Multi-Function General Purpose Timer usage (for AMD Geode machines). nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to shutdown the other cpus. Instead use the REBOOT_VECTOR irq. nomodeset Disable kernel modesetting. Most systems' firmware sets up a display mode and provides framebuffer memory for output. With nomodeset, DRM and fbdev drivers will not load if they could possibly displace the pre- initialized output. Only the system framebuffer will be available for use. The respective drivers will not perform display-mode changes or accelerated rendering. Useful as error fallback, or for testing and debugging. nomodule Disable module load nopat [X86] Disable PAT (page attribute table extension of pagetables) support. nopcid [X86-64] Disable the PCID cpu feature. nopku [X86] Disable Memory Protection Keys CPU feature found in some Intel CPUs. nopv= [X86,XEN,KVM,HYPER_V,VMWARE] Disables the PV optimizations forcing the guest to run as generic guest with no PV drivers. Currently support XEN HVM, KVM, HYPER_V and VMWARE guest. nopvspin [X86,XEN,KVM] Disables the qspinlock slow path using PV optimizations which allow the hypervisor to 'idle' the guest on lock contention. norandmaps Don't use address space randomization. Equivalent to echo 0 > /proc/sys/kernel/randomize_va_space noreplace-smp [X86-32,SMP] Don't replace SMP instructions with UP alternatives noresume [SWSUSP] Disables resume and restores original swap space. no-scroll [VGA] Disables scrollback. This is required for the Braillex ib80-piezo Braille reader made by F.H. Papenmeier (Germany). nosbagart [IA-64] nosgx [X86-64,SGX] Disables Intel SGX kernel support. nosmp [SMP] Tells an SMP kernel to act as a UP kernel, and disable the IO APIC. legacy for "maxcpus=0". nosoftlockup [KNL] Disable the soft-lockup detector. nosync [HW,M68K] Disables sync negotiation for all devices. nowatchdog [KNL] Disable both lockup detectors, i.e. soft-lockup and NMI watchdog (hard-lockup). nowb [ARM] nox2apic [X86-64,APIC] Do not enable x2APIC mode. NOTE: this parameter will be ignored on systems with the LEGACY_XAPIC_DISABLED bit set in the IA32_XAPIC_DISABLE_STATUS MSR. nps_mtm_hs_ctr= [KNL,ARC] This parameter sets the maximum duration, in cycles, each HW thread of the CTOP can run without interruptions, before HW switches it. The actual maximum duration is 16 times this parameter's value. Format: integer between 1 and 255 Default: 255 nptcg= [IA-64] Override max number of concurrent global TLB purges which is reported from either PAL_VM_SUMMARY or SAL PALO. nr_cpus= [SMP] Maximum number of processors that an SMP kernel could support. nr_cpus=n : n >= 1 limits the kernel to support 'n' processors. It could be larger than the number of already plugged CPU during bootup, later in runtime you can physically add extra cpu until it reaches n. So during boot up some boot time memory for per-cpu variables need be pre-allocated for later physical cpu hot plugging. nr_uarts= [SERIAL] maximum number of UARTs to be registered. numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only set up a single NUMA node spanning all memory. numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic NUMA balancing. Allowed values are enable and disable numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 'node', 'default' can be specified This can be set from sysctl after boot. See Documentation/admin-guide/sysctl/vm.rst for details. ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. See Documentation/core-api/debugging-via-ohci1394.rst for more info. olpc_ec_timeout= [OLPC] ms delay when issuing EC commands Rather than timing out after 20 ms if an EC command is not properly ACKed, override the length of the timeout. We have interrupts disabled while waiting for the ACK, so if this is set too high interrupts *may* be lost! omap_mux= [OMAP] Override bootloader pin multiplexing. Format: <mux_mode0.mode_name=value>... For example, to override I2C bus2: omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] boundary - index of last SLC block on Flex-OneNAND. The remaining blocks are configured as MLC blocks. lock - Configure if Flex-OneNAND boundary should be locked. Once locked, the boundary cannot be changed. 1 indicates lock status, 0 indicates unlock status. oops=panic Always panic on oopses. Default is to just kill the process, but there is a small probability of deadlocking the machine. This will also cause panics on machine check exceptions. Useful together with panic=30 to trigger a reboot. page_alloc.shuffle= [KNL] Boolean flag to control whether the page allocator should randomize its free lists. The randomization may be automatically enabled if the kernel detects it is running on a platform with a direct-mapped memory-side cache, and this parameter can be used to override/disable that behavior. The state of the flag can be read from sysfs at: /sys/module/page_alloc/parameters/shuffle. page_owner= [KNL] Boot-time page_owner enabling option. Storage of the information about who allocated each page is disabled in default. With this switch, we can turn it on. on: enable the feature page_poison= [KNL] Boot-time parameter changing the state of poisoning on the buddy allocator, available with CONFIG_PAGE_POISONING=y. off: turn off poisoning (default) on: turn on poisoning page_reporting.page_reporting_order= [KNL] Minimal page reporting order Format: <integer> Adjust the minimal page reporting order. The page reporting is disabled when it exceeds (MAX_ORDER-1). panic= [KNL] Kernel behaviour on panic: delay <timeout> timeout > 0: seconds before rebooting timeout = 0: wait forever timeout < 0: reboot immediately Format: <timeout> panic_print= Bitmask for printing system info when panic happens. User can chose combination of the following bits: bit 0: print all tasks info bit 1: print system memory info bit 2: print timer info bit 3: print locks info if CONFIG_LOCKDEP is on bit 4: print ftrace buffer bit 5: print all printk messages in buffer bit 6: print all CPUs backtrace (if available in the arch) *Be aware* that this option may print a _lot_ of lines, so there are risks of losing older messages in the log. Use this option carefully, maybe worth to setup a bigger log buffer with "log_buf_len" along with this. panic_on_taint= Bitmask for conditionally calling panic() in add_taint() Format: <hex>[,nousertaint] Hexadecimal bitmask representing the set of TAINT flags that will cause the kernel to panic when add_taint() is called with any of the flags in this set. The optional switch "nousertaint" can be utilized to prevent userspace forced crashes by writing to sysctl /proc/sys/kernel/tainted any flagset matching with the bitmask set on panic_on_taint. See Documentation/admin-guide/tainted-kernels.rst for extra details on the taint flags that users can pick to compose the bitmask to assign to panic_on_taint. panic_on_warn panic() instead of WARN(). Useful to cause kdump on a WARN(). parkbd.port= [HW] Parallel port number the keyboard adapter is connected to, default is 0. Format: <parport#> parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 0 for XT, 1 for AT (default is AT). Format: <mode> parport= [HW,PPT] Specify parallel ports. 0 disables. Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } Use 'auto' to force the driver to use any IRQ/DMA settings detected (the default is to ignore detected IRQ/DMA settings because of possible conflicts). You can specify the base address, IRQ, and DMA settings; IRQ and DMA should be numbers, or 'auto' (for using detected settings on that particular port), or 'nofifo' (to avoid using a FIFO even if it is detected). Parallel ports are assigned in the order they are specified on the command line, starting with parport0. parport_init_mode= [HW,PPT] Configure VIA parallel port to operate in a specific mode. This is necessary on Pegasos computer where firmware has no options for setting up parallel port mode and sets it to spp. Currently this function knows 686a and 8231 chips. Format: [spp|ps2|epp|ecp|ecpepp] pata_legacy.all= [HW,LIBATA] Format: <int> Set to non-zero to probe primary and secondary ISA port ranges on PCI systems where no PCI PATA device has been found at either range. Disabled by default. pata_legacy.autospeed= [HW,LIBATA] Format: <int> Set to non-zero if a chip is present that snoops speed changes. Disabled by default. pata_legacy.ht6560a= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for HT 6560A on the primary channel, the secondary channel, or both channels respectively. Disabled by default. pata_legacy.ht6560b= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for HT 6560B on the primary channel, the secondary channel, or both channels respectively. Disabled by default. pata_legacy.iordy_mask= [HW,LIBATA] Format: <int> IORDY enable mask. Set individual bits to allow IORDY for the respective channel. Bit 0 is for the first legacy channel handled by this driver, bit 1 is for the second channel, and so on. The sequence will often correspond to the primary legacy channel, the secondary legacy channel, and so on, but the handling of a PCI bus and the use of other driver options may interfere with the sequence. By default IORDY is allowed across all channels. pata_legacy.opti82c46x= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for Opti 82c611A on the primary channel, the secondary channel, or both channels respectively. Disabled by default. pata_legacy.opti82c611a= [HW,LIBATA] Format: <int> Set to 1, 2, or 3 for Opti 82c465MV on the primary channel, the secondary channel, or both channels respectively. Disabled by default. pata_legacy.pio_mask= [HW,LIBATA] Format: <int> PIO mode mask for autospeed devices. Set individual bits to allow the use of the respective PIO modes. Bit 0 is for mode 0, bit 1 is for mode 1, and so on. All modes allowed by default. pata_legacy.probe_all= [HW,LIBATA] Format: <int> Set to non-zero to probe tertiary and further ISA port ranges on PCI systems. Disabled by default. pata_legacy.probe_mask= [HW,LIBATA] Format: <int> Probe mask for legacy ISA PATA ports. Depending on platform configuration and the use of other driver options up to 6 legacy ports are supported: 0x1f0, 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing of individual ports can be disabled by setting the corresponding bits in the mask to 1. Bit 0 is for the first port in the list above (0x1f0), and so on. By default all supported ports are probed. pata_legacy.qdi= [HW,LIBATA] Format: <int> Set to non-zero to probe QDI controllers. By default set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. pata_legacy.winbond= [HW,LIBATA] Format: <int> Set to non-zero to probe Winbond controllers. Use the standard I/O port (0x130) if 1, otherwise the value given is the I/O port to use (typically 0x1b0). By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 0 otherwise. pata_platform.pio_mask= [HW,LIBATA] Format: <int> Supported PIO mode mask. Set individual bits to allow the use of the respective PIO modes. Bit 0 is for mode 0, bit 1 is for mode 1, and so on. Mode 0 only allowed by default. pause_on_oops= Halt all CPUs after the first oops has been printed for the specified number of seconds. This is to be used if your oopses keep scrolling off the screen. pcbit= [HW,ISDN] pci=option[,option...] [PCI] various PCI subsystem options. Some options herein operate on a specific device or a set of devices (<pci_dev>). These are specified in one of the following formats: [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* pci:<vendor>:<device>[:<subvendor>:<subdevice>] Note: the first format specifies a PCI bus/device/function address which may change if new hardware is inserted, if motherboard firmware changes, or due to changes caused by other kernel parameters. If the domain is left unspecified, it is taken to be zero. Optionally, a path to a device through multiple device/function addresses can be specified after the base address (this is more robust against renumbering issues). The second format selects devices using IDs from the configuration space which may match multiple devices in the system. earlydump dump PCI config space before the kernel changes anything off [X86] don't probe for the PCI bus bios [X86-32] force use of PCI BIOS, don't access the hardware directly. Use this if your machine has a non-standard PCI host bridge. nobios [X86-32] disallow use of PCI BIOS, only direct hardware access methods are allowed. Use this if you experience crashes upon bootup and you suspect they are caused by the BIOS. conf1 [X86] Force use of PCI Configuration Access Mechanism 1 (config address in IO port 0xCF8, data in IO port 0xCFC, both 32-bit). conf2 [X86] Force use of PCI Configuration Access Mechanism 2 (IO port 0xCF8 is an 8-bit port for the function, IO port 0xCFA, also 8-bit, sets bus number. The config space is then accessed through ports 0xC000-0xCFFF). See for more info on the configuration access mechanisms. noaer [PCIE] If the PCIEAER kernel config parameter is enabled, this kernel boot option can be used to disable the use of PCIE advanced error reporting. nodomains [PCI] Disable support for multiple PCI root domains (aka PCI segments, in ACPI-speak). nommconf [X86] Disable use of MMCONFIG for PCI Configuration check_enable_amd_mmconf [X86] check for and enable properly configured MMIO access to PCI config space on AMD family 10h CPU nomsi [MSI] If the PCI_MSI kernel config parameter is enabled, this kernel boot option can be used to disable the use of MSI interrupts system-wide. noioapicquirk [APIC] Disable all boot interrupt quirks. Safety option to keep boot IRQs enabled. This should never be necessary. ioapicreroute [APIC] Enable rerouting of boot IRQs to the primary IO-APIC for bridges that cannot disable boot IRQs. This fixes a source of spurious IRQs when the system masks IRQs. noioapicreroute [APIC] Disable workaround that uses the boot IRQ equivalent of an IRQ that connects to a chipset where boot IRQs cannot be disabled. The opposite of ioapicreroute. biosirq [X86-32] Use PCI BIOS calls to get the interrupt routing table. These calls are known to be buggy on several machines and they hang the machine when used, but on other computers it's the only way to get the interrupt routing table. Try this option if the kernel is unable to allocate IRQs or discover secondary PCI buses on your motherboard. rom [X86] Assign address space to expansion ROMs. Use with caution as certain devices share address decoders between ROMs and other resources. norom [X86] Do not assign address space to expansion ROMs that do not already have BIOS assigned address ranges. nobar [X86] Do not assign address space to the BARs that weren't assigned by the BIOS. irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be assigned automatically to PCI devices. You can make the kernel exclude IRQs of your ISA cards this way. pirqaddr=0xAAAAA [X86] Specify the physical address of the PIRQ table (normally generated by the BIOS) if it is outside the F0000h-100000h range. lastbus=N [X86] Scan all buses thru bus #N. Can be useful if the kernel is unable to find your secondary buses and you want to tell it explicitly which ones they are. assign-busses [X86] Always assign all PCI bus numbers ourselves, overriding whatever the firmware may have done. usepirqmask [X86] Honor the possible IRQ mask stored in the BIOS $PIR table. This is needed on some systems with broken BIOSes, notably some HP Pavilion N5400 and Omnibook XE3 notebooks. This will have no effect if ACPI IRQ routing is enabled. noacpi [X86] Do not use ACPI for IRQ routing or for PCI scanning. use_crs [X86] Use PCI host bridge window information from ACPI. On BIOSes from 2008 or later, this is enabled by default. If you need to use this, please report a bug. nocrs [X86] Ignore PCI host bridge windows from ACPI. If you need to use this, please report a bug. use_e820 [X86] Use E820 reservations to exclude parts of PCI host bridge windows. This is a workaround for BIOS defects in host bridge _CRS methods. If you need to use this, please report a bug to <>. no_e820 [X86] Ignore E820 reservations for PCI host bridge windows. This is the default on modern hardware. If you need to use this, please report a bug to <>. routeirq Do IRQ routing for all PCI devices. This is normally done in pci_enable_device(), so this option is a temporary workaround for broken drivers that don't call it. skip_isa_align [X86] do not align io start addr, so can handle more pci cards noearly [X86] Don't do any early type 1 scanning. This might help on some broken boards which machine check when some devices' config space is read. But various workarounds are disabled and some IOMMU drivers will not work. bfsort Sort PCI devices into breadth-first order. This sorting is done to get a device order compatible with older (<= 2.4) kernels. nobfsort Don't sort PCI devices into breadth-first order. pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) tuning and use the BIOS-configured MPS defaults. pcie_bus_safe Set every device's MPS to the largest value supported by all devices below the root complex. pcie_bus_perf Set device MPS to the largest allowable MPS based on its parent bus. Also set MRRS (Max Read Request Size) to the largest supported value (no larger than the MPS that the device or bus can support) for best performance. pcie_bus_peer2peer Set every device's MPS to 128B, which every device is guaranteed to support. This configuration allows peer-to-peer DMA between any pair of devices, possibly at the cost of reduced performance. This also guarantees that hot-added devices will work. cbiosize=nn[KMG] The fixed amount of bus space which is reserved for the CardBus bridge's IO window. The default value is 256 bytes. cbmemsize=nn[KMG] The fixed amount of bus space which is reserved for the CardBus bridge's memory window. The default value is 64 megabytes. resource_alignment= Format: [<order of align>@]<pci_dev>[; ...] Specifies alignment and device to reassign aligned memory resources. How to specify the device is described above. If <order of align> is not specified, PAGE_SIZE is used as alignment. A PCI-PCI bridge can be specified if resource windows need to be expanded. To specify the alignment for several instances of a device, the PCI vendor, device, subvendor, and subdevice may be specified, e.g., 12@pci:8086:9c22:103c:198f for 4096-byte alignment. ecrc= Enable/disable PCIe ECRC (transaction layer end-to-end CRC checking). Only effective if OS has native AER control (either granted by ACPI _OSC or forced via "pcie_ports=native") bios: Use BIOS/firmware settings. This is the the default. off: Turn ECRC off on: Turn ECRC on. hpiosize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's IO window. Default size is 256 bytes. hpmmiosize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's MMIO window. Default size is 2 megabytes. hpmmioprefsize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's MMIO_PREF window. Default size is 2 megabytes. hpmemsize=nn[KMG] The fixed amount of bus space which is reserved for hotplug bridge's MMIO and MMIO_PREF window. Default size is 2 megabytes. hpbussize=nn The minimum amount of additional bus numbers reserved for buses below a hotplug bridge. Default is 1. realloc= Enable/disable reallocating PCI bridge resources if allocations done by BIOS are too small to accommodate resources required by all child devices. off: Turn realloc off on: Turn realloc on realloc same as realloc=on noari do not use PCIe ARI. noats [PCIE, Intel-IOMMU, AMD-IOMMU] do not use PCIe ATS (and IOMMU device IOTLB). pcie_scan_all Scan all possible PCIe devices. Otherwise we only look for one device below a PCIe downstream port. big_root_window Try to add a big 64bit memory window to the PCIe root complex on AMD CPUs. Some GFX hardware can resize a BAR to allow access to all VRAM. Adding the window is slightly risky (it may conflict with unreported devices), so this taints the kernel. disable_acs_redir=<pci_dev>[; ...] Specify one or more PCI devices (in the format specified above) separated by semicolons. Each device specified will have the PCI ACS redirect capabilities forced off which will allow P2P traffic between devices through bridges without forcing it upstream. Note: this removes isolation between devices and may put more devices in an IOMMU group. force_floating [S390] Force usage of floating interrupts. nomio [S390] Do not use MIO instructions. norid [S390] ignore the RID field and force use of one PCI domain per PCI function pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power Management. off Disable ASPM. force Enable ASPM even on devices that claim not to support it. WARNING: Forcing ASPM on may cause system lockups. pcie_ports= [PCIE] PCIe port services handling: native Use native PCIe services (PME, AER, DPC, PCIe hotplug) even if the platform doesn't give the OS permission to use them. This may cause conflicts if the platform also tries to use these services. dpc-native Use native PCIe service for DPC only. May cause conflicts if firmware uses AER or DPC. compat Disable native PCIe services (PME, AER, DPC, PCIe hotplug). pcie_port_pm= [PCIE] PCIe port power management handling: off Disable power management of all PCIe ports force Forcibly enable power management of all PCIe ports pcie_pme= [PCIE,PM] Native PCIe PME signaling options: nomsi Do not use MSI for native PCIe PME signaling (this makes all PCIe root ports use INTx for all services). pcmv= [HW,PCMCIA] BadgePAD 4 pd_ignore_unused [PM] Keep all power-domains already enabled by bootloader on, even if no driver has claimed them. This is useful for debug and development, but should not be needed on a platform with proper driver support. pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at boot time. Format: { 0 | 1 } See arch/parisc/kernel/pdc_chassis.c percpu_alloc= Select which percpu first chunk allocator to use. Currently supported values are "embed" and "page". Archs may support subset or none of the selections. See comments in mm/percpu.c for details on each allocator. This parameter is primarily for debugging and performance comparison. pirq= [SMP,APIC] Manual mp-table setup See Documentation/x86/i386/IO-APIC.rst. plip= [PPT,NET] Parallel port network link Format: { parport<nr> | timid | 0 } See also Documentation/admin-guide/parport.rst. pmtmr= [X86] Manual setup of pmtmr I/O Port. Override pmtimer IOPort with a hex value. e.g. pmtmr=0x508 pmu_override= [PPC] Override the PMU. This option takes over the PMU facility, so it is no longer usable by perf. Setting this option starts the PMU counters by setting MMCR0 to 0 (the FC bit is cleared). If a number is given, then MMCR1 is set to that number, otherwise (e.g., 'pmu_override=on'), MMCR1 remains 0. pm_debug_messages [SUSPEND,KNL] Enable suspend/resume debug messages during boot up. pnp.debug=1 [PNP] Enable PNP debug messages (depends on the CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time via /sys/module/pnp/parameters/debug. We always show current resource usage; turning this on also shows possible settings and some assignment information. pnpacpi= [ACPI] { off } pnpbios= [ISAPNP] { on | off | curr | res | no-curr | no-res } pnp_reserve_irq= [ISAPNP] Exclude IRQs for the autoconfiguration pnp_reserve_dma= [ISAPNP] Exclude DMAs for the autoconfiguration pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration Ranges are in pairs (I/O port base and size). pnp_reserve_mem= [ISAPNP] Exclude memory regions for the autoconfiguration. Ranges are in pairs (memory base and size). ports= [IP_VS_FTP] IPVS ftp helper module Default is 21. Up to 8 (IP_VS_APP_MAX_PORTS) ports may be specified. Format: <port>,<port>.... powersave=off [PPC] This option disables power saving features. It specifically disables cpuidle and sets the platform machine description specific power_save function to NULL. On Idle the CPU just reduces execution priority. ppc_strict_facility_enable [PPC] This option catches any kernel floating point, Altivec, VSX and SPE outside of regions specifically allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). There is some performance impact when enabling this. ppc_tm= [PPC] Format: {"off"} Disable Hardware Transactional Memory preempt= [KNL] Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC none - Limited to cond_resched() calls voluntary - Limited to cond_resched() and might_sleep() calls full - Any section that isn't explicitly preempt disabled can be preempted anytime. print-fatal-signals= [KNL] debug: print fatal signals If enabled, warn about various signal handling related application anomalies: too many signals, too many POSIX.1 timers, fatal signals causing a coredump - etc. If you hit the warning due to signal overflow, you might want to try "ulimit -i unlimited". default: off. printk.always_kmsg_dump= Trigger kmsg_dump for cases other than kernel oops or panics Format: <bool> (1/Y/y=enable, 0/N/n=disable) default: disabled printk.console_no_auto_verbose= Disable console loglevel raise on oops, panic or lockdep-detected issues (only if lock debug is on). With an exception to setups with low baudrate on serial console, keeping this 0 is a good choice in order to provide more debug information. Format: <bool> default: 0 (auto_verbose is enabled) printk.devkmsg={on,off,ratelimit} Control writing to /dev/kmsg. on - unlimited logging to /dev/kmsg from userspace off - logging to /dev/kmsg disabled ratelimit - ratelimit the logging Default: ratelimit printk.time= Show timing data prefixed to each printk message line Format: <bool> (1/Y/y=enable, 0/N/n=disable) processor.max_cstate= [HW,ACPI] Limit processor to maximum C-state max_cstate=9 overrides any DMI blacklist limit. processor.nocst [HW,ACPI] Ignore the _CST method to determine C-states, instead using the legacy FADT method profile= [KNL] Enable kernel profiling via /proc/profile Format: [<profiletype>,]<number> Param: <profiletype>: "schedule", "sleep", or "kvm" [defaults to kernel profiling] Param: "schedule" - profile schedule points. Param: "sleep" - profile D-state sleeping (millisecs). Requires CONFIG_SCHEDSTATS Param: "kvm" - profile VM exits. Param: <number> - step/bucket size as a power of 2 for statistical time based profiling. prompt_ramdisk= [RAM] [Deprecated] prot_virt= [S390] enable hosting protected virtual machines isolated from the hypervisor (if hardware supports that). Format: <bool> psi= [KNL] Enable or disable pressure stall information tracking. Format: <bool> psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to probe for; one of (bare|imps|exps|lifebook|any). psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports per second. psmouse.resetafter= [HW,MOUSE] Try to reset the device after so many bad packets (0 = never). psmouse.resolution= [HW,MOUSE] Set desired mouse resolution, in dpi. psmouse.smartscroll= [HW,MOUSE] Controls Logitech smartscroll autorepeat. 0 = disabled, 1 = enabled (default). pstore.backend= Specify the name of the pstore backend to use pti= [X86-64] Control Page Table Isolation of user and kernel address spaces. Disabling this feature removes hardening, but improves performance of system calls and interrupts. on - unconditionally enable off - unconditionally disable auto - kernel detects whether your CPU model is vulnerable to issues that PTI mitigates Not specifying this option is equivalent to pti=auto. nopti [X86-64] Equivalent to pti=off pty.legacy_count= [KNL] Number of legacy pty's. Overwrites compiled-in default number. quiet [KNL] Disable most log messages r128= [HW,DRM] radix_hcall_invalidate=on [PPC/PSERIES] Disable RADIX GTSE feature and use hcall for TLB invalidate. raid= [HW,RAID] See Documentation/admin-guide/md.rst. ramdisk_size= [RAM] Sizes of RAM disks in kilobytes See Documentation/admin-guide/blockdev/ramdisk.rst. ramdisk_start= [RAM] RAM disk image start address random.trust_cpu=off [KNL] Disable trusting the use of the CPU's random number generator (if available) to initialize the kernel's RNG. random.trust_bootloader=off [KNL] Disable trusting the use of the a seed passed by the bootloader (if available) to initialize the kernel's RNG. randomize_kstack_offset= [KNL] Enable or disable kernel stack offset randomization, which provides roughly 5 bits of entropy, frustrating memory corruption attacks that depend on stack address determinism or cross-syscall address exposures. This is only available on architectures that have defined CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. Format: <bool> (1/Y/y=enable, 0/N/n=disable) Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. ras=option[,option,...] [KNL] RAS-specific options cec_disable [X86] Disable the Correctable Errors Collector, see CONFIG_RAS_CEC help text. rcu_nocbs[=cpu-list] [KNL] The optional argument is a cpu list, as described above. In kernels built with CONFIG_RCU_NOCB_CPU=y, enable the no-callback CPU mode, which prevents such CPUs' callbacks from being invoked in softirq context. Invocation of such CPUs' RCU callbacks will instead be offloaded to "rcuox/N" kthreads created for that purpose, where "x" is "p" for RCU-preempt, "s" for RCU-sched, and "g" for the kthreads that mediate grace periods; and "N" is the CPU number. This reduces OS jitter on the offloaded CPUs, which can be useful for HPC and real-time workloads. It can also improve energy efficiency for asymmetric multiprocessors. If a cpulist is passed as an argument, the specified list of CPUs is set to no-callback mode from boot. Otherwise, if the '=' sign and the cpulist arguments are omitted, no CPU will be set to no-callback mode from boot but the mode may be toggled at runtime via cpusets. Note that this argument takes precedence over the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. rcu_nocb_poll [KNL] Rather than requiring that offloaded CPUs (specified by rcu_nocbs= above) explicitly awaken the corresponding "rcuoN" kthreads, make these kthreads poll for callbacks. This improves the real-time response for the offloaded CPUs by relieving them of the need to wake up the corresponding kthread, but degrades energy efficiency by requiring that the kthreads periodically wake up to do the polling. rcutree.blimit= [KNL] Set maximum number of finished RCU callbacks to process in one batch. rcutree.dump_tree= [KNL] Dump the structure of the rcu_node combining tree out at early boot. This is used for diagnostic purposes, to verify correct tree setup. rcutree.gp_cleanup_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period cleanup. rcutree.gp_init_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period initialization. rcutree.gp_preinit_delay= [KNL] Set the number of jiffies to delay each step of RCU grace-period pre-initialization, that is, the propagation of recent CPU-hotplug changes up the rcu_node combining tree. rcutree.use_softirq= [KNL] If set to zero, move all RCU_SOFTIRQ processing to per-CPU rcuc kthreads. Defaults to a non-zero value, meaning that RCU_SOFTIRQ is used by default. Specify rcutree.use_softirq=0 to use rcuc kthreads. But note that CONFIG_PREEMPT_RT=y kernels disable this kernel boot parameter, forcibly setting it to zero. rcutree.rcu_fanout_exact= [KNL] Disable autobalancing of the rcu_node combining tree. This is used by rcutorture, and might possibly be useful for architectures having high cache-to-cache transfer latencies. rcutree.rcu_fanout_leaf= [KNL] Change the number of CPUs assigned to each leaf rcu_node structure. Useful for very large systems, which will choose the value 64, and for NUMA systems with large remote-access latencies, which will choose a value aligned with the appropriate hardware boundaries. rcutree.rcu_min_cached_objs= [KNL] Minimum number of objects which are cached and maintained per one CPU. Object size is equal to PAGE_SIZE. The cache allows to reduce the pressure to page allocator, also it makes the whole algorithm to behave better in low memory condition. rcutree.rcu_delay_page_cache_fill_msec= [KNL] Set the page-cache refill delay (in milliseconds) in response to low-memory conditions. The range of permitted values is in the range 0:100000. rcutree.jiffies_till_first_fqs= [KNL] Set delay from grace-period initialization to first attempt to force quiescent states. Units are jiffies, minimum value is zero, and maximum value is HZ. rcutree.jiffies_till_next_fqs= [KNL] Set delay between subsequent attempts to force quiescent states. Units are jiffies, minimum value is one, and maximum value is HZ. rcutree.jiffies_till_sched_qs= [KNL] Set required age in jiffies for a given grace period before RCU starts soliciting quiescent-state help from rcu_note_context_switch() and cond_resched(). If not specified, the kernel will calculate a value based on the most recent settings of rcutree.jiffies_till_first_fqs and rcutree.jiffies_till_next_fqs. This calculated value may be viewed in rcutree.jiffies_to_sched_qs. Any attempt to set rcutree.jiffies_to_sched_qs will be cheerfully overwritten. rcutree.kthread_prio= [KNL,BOOT] Set the SCHED_FIFO priority of the RCU per-CPU kthreads (rcuc/N). This value is also used for the priority of the RCU boost threads (rcub/N) and for the RCU grace-period kthreads (rcu_bh, rcu_preempt, and rcu_sched). If RCU_BOOST is set, valid values are 1-99 and the default is 1 (the least-favored priority). Otherwise, when RCU_BOOST is not set, valid values are 0-99 and the default is zero (non-realtime operation). When RCU_NOCB_CPU is set, also adjust the priority of NOCB callback kthreads. rcutree.rcu_divisor= [KNL] Set the shift-right count to use to compute the callback-invocation batch limit bl from the number of callbacks queued on this CPU. The result will be bounded below by the value of the rcutree.blimit kernel parameter. Every bl callbacks, the softirq handler will exit in order to allow the CPU to do other work. Please note that this callback-invocation batch limit applies only to non-offloaded callback invocation. Offloaded callbacks are instead invoked in the context of an rcuoc kthread, which scheduler will preempt as it does any other task. rcutree.nocb_nobypass_lim_per_jiffy= [KNL] On callback-offloaded (rcu_nocbs) CPUs, RCU reduces the lock contention that would otherwise be caused by callback floods through use of the ->nocb_bypass list. However, in the common non-flooded case, RCU queues directly to the main ->cblist in order to avoid the extra overhead of the ->nocb_bypass list and its lock. But if there are too many callbacks queued during a single jiffy, RCU pre-queues the callbacks into the ->nocb_bypass queue. The definition of "too many" is supplied by this kernel boot parameter. rcutree.rcu_nocb_gp_stride= [KNL] Set the number of NOCB callback kthreads in each group, which defaults to the square root of the number of CPUs. Larger numbers reduce the wakeup overhead on the global grace-period kthread, but increases that same overhead on each group's NOCB grace-period kthread. rcutree.qhimark= [KNL] Set threshold of queued RCU callbacks beyond which batch limiting is disabled. rcutree.qlowmark= [KNL] Set threshold of queued RCU callbacks below which batch limiting is re-enabled. rcutree.qovld= [KNL] Set threshold of queued RCU callbacks beyond which RCU's force-quiescent-state scan will aggressively enlist help from cond_resched() and sched IPIs to help CPUs more quickly reach quiescent states. Set to less than zero to make this be set based on rcutree.qhimark at boot time and to zero to disable more aggressive help enlistment. rcutree.rcu_kick_kthreads= [KNL] Cause the grace-period kthread to get an extra wake_up() if it sleeps three times longer than it should at force-quiescent-state time. This wake_up() will be accompanied by a WARN_ONCE() splat and an ftrace_dump(). rcutree.rcu_unlock_delay= [KNL] In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, this specifies an rcu_read_unlock()-time delay in microseconds. This defaults to zero. Larger delays increase the probability of catching RCU pointer leaks, that is, buggy use of RCU-protected pointers after the relevant rcu_read_unlock() has completed. rcutree.sysrq_rcu= [KNL] Commandeer a sysrq key to dump out Tree RCU's rcu_node tree with an eye towards determining why a new grace period has not yet started. rcuscale.gp_async= [KNL] Measure performance of asynchronous grace-period primitives such as call_rcu(). rcuscale.gp_async_max= [KNL] Specify the maximum number of outstanding callbacks per writer thread. When a writer thread exceeds this limit, it invokes the corresponding flavor of rcu_barrier() to allow previously posted callbacks to drain. rcuscale.gp_exp= [KNL] Measure performance of expedited synchronous grace-period primitives. rcuscale.holdoff= [KNL] Set test-start holdoff period. The purpose of this parameter is to delay the start of the test until boot completes in order to avoid interference. rcuscale.kfree_rcu_test= [KNL] Set to measure performance of kfree_rcu() flooding. rcuscale.kfree_rcu_test_double= [KNL] Test the double-argument variant of kfree_rcu(). If this parameter has the same value as rcuscale.kfree_rcu_test_single, both the single- and double-argument variants are tested. rcuscale.kfree_rcu_test_single= [KNL] Test the single-argument variant of kfree_rcu(). If this parameter has the same value as rcuscale.kfree_rcu_test_double, both the single- and double-argument variants are tested. rcuscale.kfree_nthreads= [KNL] The number of threads running loops of kfree_rcu(). rcuscale.kfree_alloc_num= [KNL] Number of allocations and frees done in an iteration. rcuscale.kfree_loops= [KNL] Number of loops doing rcuscale.kfree_alloc_num number of allocations and frees. rcuscale.nreaders= [KNL] Set number of RCU readers. The value -1 selects N, where N is the number of CPUs. A value "n" less than -1 selects N-n+1, where N is again the number of CPUs. For example, -2 selects N (the number of CPUs), -3 selects N+1, and so on. A value of "n" less than or equal to -N selects a single reader. rcuscale.nwriters= [KNL] Set number of RCU writers. The values operate the same as for rcuscale.nreaders. N, where N is the number of CPUs rcuscale.perf_type= [KNL] Specify the RCU implementation to test. rcuscale.shutdown= [KNL] Shut the system down after performance tests complete. This is useful for hands-off automated testing. rcuscale.verbose= [KNL] Enable additional printk() statements. rcuscale.writer_holdoff= [KNL] Write-side holdoff between grace periods, in microseconds. The default of zero says no holdoff. rcutorture.fqs_duration= [KNL] Set duration of force_quiescent_state bursts in microseconds. rcutorture.fqs_holdoff= [KNL] Set holdoff time within force_quiescent_state bursts in microseconds. rcutorture.fqs_stutter= [KNL] Set wait time between force_quiescent_state bursts in seconds. rcutorture.fwd_progress= [KNL] Specifies the number of kthreads to be used for RCU grace-period forward-progress testing for the types of RCU supporting this notion. Defaults to 1 kthread, values less than zero or greater than the number of CPUs cause the number of CPUs to be used. rcutorture.fwd_progress_div= [KNL] Specify the fraction of a CPU-stall-warning period to do tight-loop forward-progress testing. rcutorture.fwd_progress_holdoff= [KNL] Number of seconds to wait between successive forward-progress tests. rcutorture.fwd_progress_need_resched= [KNL] Enclose cond_resched() calls within checks for need_resched() during tight-loop forward-progress testing. rcutorture.gp_cond= [KNL] Use conditional/asynchronous update-side primitives, if available. rcutorture.gp_exp= [KNL] Use expedited update-side primitives, if available. rcutorture.gp_normal= [KNL] Use normal (non-expedited) asynchronous update-side primitives, if available. rcutorture.gp_sync= [KNL] Use normal (non-expedited) synchronous update-side primitives, if available. If all of rcutorture.gp_cond=, rcutorture.gp_exp=, rcutorture.gp_normal=, and rcutorture.gp_sync= are zero, rcutorture acts as if is interpreted they are all non-zero. rcutorture.irqreader= [KNL] Run RCU readers from irq handlers, or, more accurately, from a timer handler. Not all RCU flavors take kindly to this sort of thing. rcutorture.leakpointer= [KNL] Leak an RCU-protected pointer out of the reader. This can of course result in splats, and is intended to test the ability of things like CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect such leaks. rcutorture.n_barrier_cbs= [KNL] Set callbacks/threads for rcu_barrier() testing. rcutorture.nfakewriters= [KNL] Set number of concurrent RCU writers. These just stress RCU, they don't participate in the actual test, hence the "fake". rcutorture.nocbs_nthreads= [KNL] Set number of RCU callback-offload togglers. Zero (the default) disables toggling. rcutorture.nocbs_toggle= [KNL] Set the delay in milliseconds between successive callback-offload toggling attempts. rcutorture.nreaders= [KNL] Set number of RCU readers. The value -1 selects N-1, where N is the number of CPUs. A value "n" less than -1 selects N-n-2, where N is again the number of CPUs. For example, -2 selects N (the number of CPUs), -3 selects N+1, and so on. rcutorture.object_debug= [KNL] Enable debug-object double-call_rcu() testing. rcutorture.onoff_holdoff= [KNL] Set time (s) after boot for CPU-hotplug testing. rcutorture.onoff_interval= [KNL] Set time (jiffies) between CPU-hotplug operations, or zero to disable CPU-hotplug testing. rcutorture.read_exit= [KNL] Set the number of read-then-exit kthreads used to test the interaction of RCU updaters and task-exit processing. rcutorture.read_exit_burst= [KNL] The number of times in a given read-then-exit episode that a set of read-then-exit kthreads is spawned. rcutorture.read_exit_delay= [KNL] The delay, in seconds, between successive read-then-exit testing episodes. rcutorture.shuffle_interval= [KNL] Set task-shuffle interval (s). Shuffling tasks allows some CPUs to go into dyntick-idle mode during the rcutorture test. rcutorture.shutdown_secs= [KNL] Set time (s) after boot system shutdown. This is useful for hands-off automated testing. rcutorture.stall_cpu= [KNL] Duration of CPU stall (s) to test RCU CPU stall warnings, zero to disable. rcutorture.stall_cpu_block= [KNL] Sleep while stalling if set. This will result in warnings from preemptible RCU in addition to any other stall-related activity. rcutorture.stall_cpu_holdoff= [KNL] Time to wait (s) after boot before inducing stall. rcutorture.stall_cpu_irqsoff= [KNL] Disable interrupts while stalling if set. rcutorture.stall_gp_kthread= [KNL] Duration (s) of forced sleep within RCU grace-period kthread to test RCU CPU stall warnings, zero to disable. If both stall_cpu and stall_gp_kthread are specified, the kthread is starved first, then the CPU. rcutorture.stat_interval= [KNL] Time (s) between statistics printk()s. rcutorture.stutter= [KNL] Time (s) to stutter testing, for example, specifying five seconds causes the test to run for five seconds, wait for five seconds, and so on. This tests RCU's ability to transition abruptly to and from idle. rcutorture.test_boost= [KNL] Test RCU priority boosting? 0=no, 1=maybe, 2=yes. "Maybe" means test if the RCU implementation under test support RCU priority boosting. rcutorture.test_boost_duration= [KNL] Duration (s) of each individual boost test. rcutorture.test_boost_interval= [KNL] Interval (s) between each boost test. rcutorture.test_no_idle_hz= [KNL] Test RCU's dyntick-idle handling. See also the rcutorture.shuffle_interval parameter. rcutorture.torture_type= [KNL] Specify the RCU implementation to test. rcutorture.verbose= [KNL] Enable additional printk() statements. rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] Dump ftrace buffer after reporting RCU CPU stall warning. rcupdate.rcu_cpu_stall_suppress= [KNL] Suppress RCU CPU stall warning messages. rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] Suppress RCU CPU stall warning messages and rcutorture writer stall warnings that occur during early boot, that is, during the time before the init task is spawned. rcupdate.rcu_cpu_stall_timeout= [KNL] Set timeout for RCU CPU stall warning messages. The value is in seconds and the maximum allowed value is 300 seconds. rcupdate.rcu_exp_cpu_stall_timeout= [KNL] Set timeout for expedited RCU CPU stall warning messages. The value is in milliseconds and the maximum allowed value is 21000 milliseconds. Please note that this value is adjusted to an arch timer tick resolution. Setting this to zero causes the value from rcupdate.rcu_cpu_stall_timeout to be used (after conversion from seconds to milliseconds). rcupdate.rcu_cpu_stall_cputime= [KNL] Provide statistics on the cputime and count of interrupts and tasks during the sampling period. For multiple continuous RCU stalls, all sampling periods begin at half of the first RCU stall timeout. rcupdate.rcu_exp_stall_task_details= [KNL] Print stack dumps of any tasks blocking the current expedited RCU grace period during an expedited RCU CPU stall warning. rcupdate.rcu_expedited= [KNL] Use expedited grace-period primitives, for example, synchronize_rcu_expedited() instead of synchronize_rcu(). This reduces latency, but can increase CPU utilization, degrade real-time latency, and degrade energy efficiency. No effect on CONFIG_TINY_RCU kernels. rcupdate.rcu_normal= [KNL] Use only normal grace-period primitives, for example, synchronize_rcu() instead of synchronize_rcu_expedited(). This improves real-time latency, CPU utilization, and energy efficiency, but can expose users to increased grace-period latency. This parameter overrides rcupdate.rcu_expedited. No effect on CONFIG_TINY_RCU kernels. rcupdate.rcu_normal_after_boot= [KNL] Once boot has completed (that is, after rcu_end_inkernel_boot() has been invoked), use only normal grace-period primitives. No effect on CONFIG_TINY_RCU kernels. But note that CONFIG_PREEMPT_RT=y kernels enables this kernel boot parameter, forcibly setting it to the value one, that is, converting any post-boot attempt at an expedited RCU grace period to instead use normal non-expedited grace-period processing. rcupdate.rcu_task_collapse_lim= [KNL] Set the maximum number of callbacks present at the beginning of a grace period that allows the RCU Tasks flavors to collapse back to using a single callback queue. This switching only occurs when rcupdate.rcu_task_enqueue_lim is set to the default value of -1. rcupdate.rcu_task_contend_lim= [KNL] Set the minimum number of callback-queuing-time lock-contention events per jiffy required to cause the RCU Tasks flavors to switch to per-CPU callback queuing. This switching only occurs when rcupdate.rcu_task_enqueue_lim is set to the default value of -1. rcupdate.rcu_task_enqueue_lim= [KNL] Set the number of callback queues to use for the RCU Tasks family of RCU flavors. The default of -1 allows this to be automatically (and dynamically) adjusted. This parameter is intended for use in testing. rcupdate.rcu_task_ipi_delay= [KNL] Set time in jiffies during which RCU tasks will avoid sending IPIs, starting with the beginning of a given grace period. Setting a large number avoids disturbing real-time workloads, but lengthens grace periods. rcupdate.rcu_task_stall_info= [KNL] Set initial timeout in jiffies for RCU task stall informational messages, which give some indication of the problem for those not patient enough to wait for ten minutes. Informational messages are only printed prior to the stall-warning message for a given grace period. Disable with a value less than or equal to zero. Defaults to ten seconds. A change in value does not take effect until the beginning of the next grace period. rcupdate.rcu_task_stall_info_mult= [KNL] Multiplier for time interval between successive RCU task stall informational messages for a given RCU tasks grace period. This value is clamped to one through ten, inclusive. It defaults to the value three, so that the first informational message is printed 10 seconds into the grace period, the second at 40 seconds, the third at 160 seconds, and then the stall warning at 600 seconds would prevent a fourth at 640 seconds. rcupdate.rcu_task_stall_timeout= [KNL] Set timeout in jiffies for RCU task stall warning messages. Disable with a value less than or equal to zero. Defaults to ten minutes. A change in value does not take effect until the beginning of the next grace period. rcupdate.rcu_self_test= [KNL] Run the RCU early boot self tests rdinit= [KNL] Format: <full_path> Run specified binary instead of /init from the ramdisk, used for early userspace startup. See initrd. rdrand= [X86] force - Override the decision by the kernel to hide the advertisement of RDRAND support (this affects certain AMD processors because of buggy BIOS support, specifically around the suspend/resume path). rdt= [HW,X86,RDT] Turn on/off individual RDT features. List is: cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, mba, smba, bmec. E.g. to turn on cmt and turn off mba use: rdt=cmt,!mba reboot= [KNL] Format (x86 or x86_64): [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ [[,]s[mp]#### \ [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ [[,]f[orce] Where reboot_mode is one of warm (soft) or cold (hard) or gpio (prefix with 'panic_' to set mode for panic reboot only), reboot_type is one of bios, acpi, kbd, triple, efi, or pci, reboot_force is either force or not specified, reboot_cpu is s[mp]#### with #### being the processor to be used for rebooting. refscale.holdoff= [KNL] Set test-start holdoff period. The purpose of this parameter is to delay the start of the test until boot completes in order to avoid interference. refscale.loops= [KNL] Set the number of loops over the synchronization primitive under test. Increasing this number reduces noise due to loop start/end overhead, but the default has already reduced the per-pass noise to a handful of picoseconds on ca. 2020 x86 laptops. refscale.nreaders= [KNL] Set number of readers. The default value of -1 selects N, where N is roughly 75% of the number of CPUs. A value of zero is an interesting choice. refscale.nruns= [KNL] Set number of runs, each of which is dumped onto the console log. refscale.readdelay= [KNL] Set the read-side critical-section duration, measured in microseconds. refscale.scale_type= [KNL] Specify the read-protection implementation to test. refscale.shutdown= [KNL] Shut down the system at the end of the performance test. This defaults to 1 (shut it down) when refscale is built into the kernel and to 0 (leave it running) when refscale is built as a module. refscale.verbose= [KNL] Enable additional printk() statements. refscale.verbose_batched= [KNL] Batch the additional printk() statements. If zero (the default) or negative, print everything. Otherwise, print every Nth verbose statement, where N is the value specified. relax_domain_level= [KNL, SMP] Set scheduler's default relax_domain_level. See Documentation/admin-guide/cgroup-v1/cpusets.rst. reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory Format: <base1>,<size1>[,<base2>,<size2>,...] Reserve I/O ports or memory so the kernel won't use them. If <base> is less than 0x10000, the region is assumed to be I/O ports; otherwise it is memory. reservetop= [X86-32] Format: nn[KMG] Reserves a hole at the top of the kernel virtual address space. reset_devices [KNL] Force drivers to reset the underlying device during initialization. resume= [SWSUSP] Specify the partition device for software suspend Format: {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} resume_offset= [SWSUSP] Specify the offset from the beginning of the partition given by "resume=" at which the swap header is located, in <PAGE_SIZE> units (needed only for swap files). See Documentation/power/swsusp-and-swap-files.rst resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to read the resume files resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices). retain_initrd [RAM] Keep initrd memory after extraction retbleed= [X86] Control mitigation of RETBleed (Arbitrary Speculative Code Execution with Return Instructions) vulnerability. AMD-based UNRET and IBPB mitigations alone do not stop sibling threads from influencing the predictions of other sibling threads. For that reason, STIBP is used on pro- cessors that support it, and mitigate SMT on processors that don't. off - no mitigation auto - automatically select a migitation auto,nosmt - automatically select a mitigation, disabling SMT if necessary for the full mitigation (only on Zen1 and older without STIBP). ibpb - On AMD, mitigate short speculation windows on basic block boundaries too. Safe, highest perf impact. It also enables STIBP if present. Not suitable on Intel. ibpb,nosmt - Like "ibpb" above but will disable SMT when STIBP is not available. This is the alternative for systems which do not have STIBP. unret - Force enable untrained return thunks, only effective on AMD f15h-f17h based systems. unret,nosmt - Like unret, but will disable SMT when STIBP is not available. This is the alternative for systems which do not have STIBP. Selecting 'auto' will choose a mitigation method at run time according to the CPU. Not specifying this option is equivalent to retbleed=auto. rfkill.default_state= 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, etc. communication is blocked by default. 1 Unblocked. rfkill.master_switch_mode= 0 The "airplane mode" button does nothing. 1 The "airplane mode" button toggles between everything blocked and the previous configuration. 2 The "airplane mode" button toggles between everything blocked and everything unblocked. rhash_entries= [KNL,NET] Set number of hash buckets for route cache ring3mwait=disable [KNL] Disable ring 3 MONITOR/MWAIT feature on supported CPUs. ro [KNL] Mount root device read-only on boot rodata= [KNL] on Mark read-only kernel memory as read-only (default). off Leave read-only kernel memory writable for debugging. full Mark read-only kernel memory and aliases as read-only [arm64] rockchip.usb_uart Enable the uart passthrough on the designated usb port on Rockchip SoCs. When active, the signals of the debug-uart get routed to the D+ and D- pins of the usb port and the regular usb controller gets disabled. root= [KNL] Root filesystem See name_to_dev_t comment in init/do_mounts.c. rootdelay= [KNL] Delay (in seconds) to pause before attempting to mount the root filesystem rootflags= [KNL] Set root filesystem mount option string rootfstype= [KNL] Set root filesystem type rootwait [KNL] Wait (indefinitely) for root device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices). rproc_mem=nn[KMG][@address] [KNL,ARM,CMA] Remoteproc physical memory block. Memory area to be used by remote processor image, managed by CMA. rw [KNL] Mount root device read-write on boot S [KNL] Run init in single mode s390_iommu= [HW,S390] Set s390 IOTLB flushing mode strict With strict flushing every unmap operation will result in an IOTLB flush. Default is lazy flushing before reuse, which is faster. s390_iommu_aperture= [KNL,S390] Specifies the size of the per device DMA address space accessible through the DMA and IOMMU APIs as a decimal factor of the size of main memory. The default is 1 meaning that one can concurrently use as many DMA addresses as physical memory is installed, if supported by hardware, and thus map all of memory once. With a value of 2 one can map all of memory twice and so on. As a special case a factor of 0 imposes no restrictions other than those given by hardware at the cost of significant additional memory use for tables. sa1100ir [NET] See drivers/net/irda/sa1100_ir.c. sched_verbose [KNL] Enables verbose scheduler debug messages. schedstats= [KNL,X86] Enable or disable scheduled statistics. Allowed values are enable and disable. This feature incurs a small amount of overhead in the scheduler but is useful for debugging and performance tuning. sched_thermal_decay_shift= [KNL, SMP] Set a decay shift for scheduler thermal pressure signal. Thermal pressure signal follows the default decay period of other scheduler pelt signals(usually 32 ms but configurable). Setting sched_thermal_decay_shift will left shift the decay period for the thermal pressure signal by the shift value. i.e. with the default pelt decay period of 32 ms sched_thermal_decay_shift thermal pressure decay pr 1 64 ms 2 128 ms and so on. Format: integer between 0 and 10 Default is 0. scftorture.holdoff= [KNL] Number of seconds to hold off before starting test. Defaults to zero for module insertion and to 10 seconds for built-in smp_call_function() tests. scftorture.longwait= [KNL] Request ridiculously long waits randomly selected up to the chosen limit in seconds. Zero (the default) disables this feature. Please note that requesting even small non-zero numbers of seconds can result in RCU CPU stall warnings, softlockup complaints, and so on. scftorture.nthreads= [KNL] Number of kthreads to spawn to invoke the smp_call_function() family of functions. The default of -1 specifies a number of kthreads equal to the number of CPUs. scftorture.onoff_holdoff= [KNL] Number seconds to wait after the start of the test before initiating CPU-hotplug operations. scftorture.onoff_interval= [KNL] Number seconds to wait between successive CPU-hotplug operations. Specifying zero (which is the default) disables CPU-hotplug operations. scftorture.shutdown_secs= [KNL] The number of seconds following the start of the test after which to shut down the system. The default of zero avoids shutting down the system. Non-zero values are useful for automated tests. scftorture.stat_interval= [KNL] The number of seconds between outputting the current test statistics to the console. A value of zero disables statistics output. scftorture.stutter_cpus= [KNL] The number of jiffies to wait between each change to the set of CPUs under test. scftorture.use_cpus_read_lock= [KNL] Use use_cpus_read_lock() instead of the default preempt_disable() to disable CPU hotplug while invoking one of the smp_call_function*() functions. scftorture.verbose= [KNL] Enable additional printk() statements. scftorture.weight_single= [KNL] The probability weighting to use for the smp_call_function_single() function with a zero "wait" parameter. A value of -1 selects the default if all other weights are -1. However, if at least one weight has some other value, a value of -1 will instead select a weight of zero. scftorture.weight_single_wait= [KNL] The probability weighting to use for the smp_call_function_single() function with a non-zero "wait" parameter. See weight_single. scftorture.weight_many= [KNL] The probability weighting to use for the smp_call_function_many() function with a zero "wait" parameter. See weight_single. Note well that setting a high probability for this weighting can place serious IPI load on the system. scftorture.weight_many_wait= [KNL] The probability weighting to use for the smp_call_function_many() function with a non-zero "wait" parameter. See weight_single and weight_many. scftorture.weight_all= [KNL] The probability weighting to use for the smp_call_function_all() function with a zero "wait" parameter. See weight_single and weight_many. scftorture.weight_all_wait= [KNL] The probability weighting to use for the smp_call_function_all() function with a non-zero "wait" parameter. See weight_single and weight_many. skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate xtime_lock contention on larger systems, and/or RCU lock contention on all systems with CONFIG_MAXSMP set. Format: { "0" | "1" } 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 1 -- enable. Note: increases power consumption, thus should only be enabled if running jitter sensitive (HPC/RT) workloads. security= [SECURITY] Choose a legacy "major" security module to enable at boot. This has been deprecated by the "lsm=" parameter. selinux= [SELINUX] Disable or enable SELinux at boot time. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- disable. 1 -- enable. Default value is 1. serialnumber [BUGS=X86-32] sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst shapers= [NET] Maximal number of shapers. show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller Limit apic dumping. The parameter defines the maximal number of local apics being dumped. Also it is possible to set it to "all" by meaning -- no limit here. Format: { 1 (default) | 2 | ... | all }. The parameter valid if only apic=debug or apic=verbose is specified. Example: apic=debug show_lapic=all simeth= [IA-64] simscsi= slram= [HW,MTD] slab_merge [MM] Enable merging of slabs with similar size when the kernel is built without CONFIG_SLAB_MERGE_DEFAULT. slab_nomerge [MM] Disable merging of slabs with similar size. May be necessary if there is some reason to distinguish allocs to different slabs, especially in hardened environments where the risk of heap overflows and layout control by attackers can usually be frustrated by disabling merging. This will reduce most of the exposure of a heap attack to a single cache (risks via metadata attacks are mostly unchanged). Debug options disable merging on their own. For more information see Documentation/mm/slub.rst. slab_max_order= [MM, SLAB] Determines the maximum allowed order for slabs. A high setting may cause OOMs due to memory fragmentation. Defaults to 1 for systems with more than 32MB of RAM, 0 otherwise. slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] Enabling slub_debug allows one to determine the culprit if slab objects become corrupted. Enabling slub_debug can create guard zones around objects and may poison objects when not in use. Also tracks the last alloc / free. For more information see Documentation/mm/slub.rst. slub_max_order= [MM, SLUB] Determines the maximum allowed order for slabs. A high setting may cause OOMs due to memory fragmentation. For more information see Documentation/mm/slub.rst. slub_min_objects= [MM, SLUB] The minimum number of objects per slab. SLUB will increase the slab order up to slub_max_order to generate a sufficiently large slab able to contain the number of objects indicated. The higher the number of objects the smaller the overhead of tracking slabs and the less frequently locks need to be acquired. For more information see Documentation/mm/slub.rst. slub_min_order= [MM, SLUB] Determines the minimum page order for slabs. Must be lower than slub_max_order. For more information see Documentation/mm/slub.rst. slub_merge [MM, SLUB] Same with slab_merge. slub_nomerge [MM, SLUB] Same with slab_nomerge. This is supported for legacy. See slab_nomerge for more information. smart2= [HW] Format: <io1>[,<io2>[,...,<io8>]] smp.csd_lock_timeout= [KNL] Specify the period of time in milliseconds that smp_call_function() and friends will wait for a CPU to release the CSD lock. This is useful when diagnosing bugs involving CPUs disabling interrupts for extended periods of time. Defaults to 5,000 milliseconds, and setting a value of zero disables this feature. This feature may be more efficiently disabled using the csdlock_debug- kernel parameter. smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port smsc-ircc2.ircc_sir= [HW] SIR base I/O port smsc-ircc2.ircc_fir= [HW] FIR base I/O port smsc-ircc2.ircc_irq= [HW] IRQ line smsc-ircc2.ircc_dma= [HW] DMA channel smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 0: Toshiba Satellite 1800 (GP data pin select) 1: Fast pin select (default) 2: ATC IRMode smt= [KNL,S390] Set the maximum number of threads (logical CPUs) to use per physical CPU on systems capable of symmetric multithreading (SMT). Will be capped to the actual hardware limit. Format: <integer> Default: -1 (no limit) softlockup_panic= [KNL] Should the soft-lockup detector generate panics. Format: 0 | 1 A value of 1 instructs the soft-lockup detector to panic the machine when a soft-lockup occurs. It is also controlled by the kernel.softlockup_panic sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the respective build-time switch to that functionality. softlockup_all_cpu_backtrace= [KNL] Should the soft-lockup detector generate backtraces on all cpus. Format: 0 | 1 sonypi.*= [HW] Sony Programmable I/O Control Device driver See Documentation/admin-guide/laptops/sonypi.rst spectre_v2= [X86] Control mitigation of Spectre variant 2 (indirect branch speculation) vulnerability. The default operation protects the kernel from user space attacks. on - unconditionally enable, implies spectre_v2_user=on off - unconditionally disable, implies spectre_v2_user=off auto - kernel detects whether your CPU model is vulnerable Selecting 'on' will, and 'auto' may, choose a mitigation method at run time according to the CPU, the available microcode, the setting of the CONFIG_RETPOLINE configuration option, and the compiler with which the kernel was built. Selecting 'on' will also enable the mitigation against user space to user space task attacks. Selecting 'off' will disable both the kernel and the user space protections. Specific mitigations can also be selected manually: retpoline - replace indirect branches retpoline,generic - Retpolines retpoline,lfence - LFENCE; indirect branch retpoline,amd - alias for retpoline,lfence eibrs - Enhanced/Auto IBRS eibrs,retpoline - Enhanced/Auto IBRS + Retpolines eibrs,lfence - Enhanced/Auto IBRS + LFENCE ibrs - use IBRS to protect kernel Not specifying this option is equivalent to spectre_v2=auto. spectre_v2_user= [X86] Control mitigation of Spectre variant 2 (indirect branch speculation) vulnerability between user space tasks on - Unconditionally enable mitigations. Is enforced by spectre_v2=on off - Unconditionally disable mitigations. Is enforced by spectre_v2=off prctl - Indirect branch speculation is enabled, but mitigation can be enabled via prctl per thread. The mitigation control state is inherited on fork. prctl,ibpb - Like "prctl" above, but only STIBP is controlled per thread. IBPB is issued always when switching between different user space processes. seccomp - Same as "prctl" above, but all seccomp threads will enable the mitigation unless they explicitly opt out. seccomp,ibpb - Like "seccomp" above, but only STIBP is controlled per thread. IBPB is issued always when switching between different user space processes. auto - Kernel selects the mitigation depending on the available CPU features and vulnerability. Default mitigation: "prctl" Not specifying this option is equivalent to spectre_v2_user=auto. spec_store_bypass_disable= [HW] Control Speculative Store Bypass (SSB) Disable mitigation (Speculative Store Bypass vulnerability) Certain CPUs are vulnerable to an exploit against a a common industry wide performance optimization known as "Speculative Store Bypass" in which recent stores to the same memory location may not be observed by later loads during speculative execution. The idea is that such stores are unlikely and that they can be detected prior to instruction retirement at the end of a particular speculation execution window. In vulnerable processors, the speculatively forwarded store can be used in a cache side channel attack, for example to read memory to which the attacker does not directly have access (e.g. inside sandboxed code). This parameter controls whether the Speculative Store Bypass optimization is used. On x86 the options are: on - Unconditionally disable Speculative Store Bypass off - Unconditionally enable Speculative Store Bypass auto - Kernel detects whether the CPU model contains an implementation of Speculative Store Bypass and picks the most appropriate mitigation. If the CPU is not vulnerable, "off" is selected. If the CPU is vulnerable the default mitigation is architecture and Kconfig dependent. See below. prctl - Control Speculative Store Bypass per thread via prctl. Speculative Store Bypass is enabled for a process by default. The state of the control is inherited on fork. seccomp - Same as "prctl" above, but all seccomp threads will disable SSB unless they explicitly opt out. Default mitigations: X86: "prctl" On powerpc the options are: on,auto - On Power8 and Power9 insert a store-forwarding barrier on kernel entry and exit. On Power7 perform a software flush on kernel entry and exit. off - No action. Not specifying this option is equivalent to spec_store_bypass_disable=auto. spia_io_base= [HW,MTD] spia_fio_base= spia_pedr= spia_peddr= split_lock_detect= [X86] Enable split lock detection or bus lock detection When enabled (and if hardware support is present), atomic instructions that access data across cache line boundaries will result in an alignment check exception for split lock detection or a debug exception for bus lock detection. off - not enabled warn - the kernel will emit rate-limited warnings about applications triggering the #AC exception or the #DB exception. This mode is the default on CPUs that support split lock detection or bus lock detection. Default behavior is by #AC if both features are enabled in hardware. fatal - the kernel will send SIGBUS to applications that trigger the #AC exception or the #DB exception. Default behavior is by #AC if both features are enabled in hardware. ratelimit:N - Set system wide rate limit to N bus locks per second for bus lock detection. 0 < N <= 1000. N/A for split lock detection. If an #AC exception is hit in the kernel or in firmware (i.e. not while executing in user mode) the kernel will oops in either "warn" or "fatal" mode. #DB exception for bus lock is triggered only when CPL > 0. srbds= [X86,INTEL] Control the Special Register Buffer Data Sampling (SRBDS) mitigation. Certain CPUs are vulnerable to an MDS-like exploit which can leak bits from the random number generator. By default, this issue is mitigated by microcode. However, the microcode fix can cause the RDRAND and RDSEED instructions to become much slower. Among other effects, this will result in reduced throughput from /dev/urandom. The microcode mitigation can be disabled with the following option: off: Disable mitigation and remove performance impact to RDRAND and RDSEED srcutree.big_cpu_lim [KNL] Specifies the number of CPUs constituting a large system, such that srcu_struct structures should immediately allocate an srcu_node array. This kernel-boot parameter defaults to 128, but takes effect only when the low-order four bits of srcutree.convert_to_big is equal to 3 (decide at boot). srcutree.convert_to_big [KNL] Specifies under what conditions an SRCU tree srcu_struct structure will be converted to big form, that is, with an rcu_node tree: 0: Never. 1: At init_srcu_struct() time. 2: When rcutorture decides to. 3: Decide at boot time (default). 0x1X: Above plus if high contention. Either way, the srcu_node tree will be sized based on the actual runtime number of CPUs (nr_cpu_ids) instead of the compile-time CONFIG_NR_CPUS. srcutree.counter_wrap_check [KNL] Specifies how frequently to check for grace-period sequence counter wrap for the srcu_data structure's ->srcu_gp_seq_needed field. The greater the number of bits set in this kernel parameter, the less frequently counter wrap will be checked for. Note that the bottom two bits are ignored. srcutree.exp_holdoff [KNL] Specifies how many nanoseconds must elapse since the end of the last SRCU grace period for a given srcu_struct until the next normal SRCU grace period will be considered for automatic expediting. Set to zero to disable automatic expediting. srcutree.srcu_max_nodelay [KNL] Specifies the number of no-delay instances per jiffy for which the SRCU grace period worker thread will be rescheduled with zero delay. Beyond this limit, worker thread will be rescheduled with a sleep delay of one jiffy. srcutree.srcu_max_nodelay_phase [KNL] Specifies the per-grace-period phase, number of non-sleeping polls of readers. Beyond this limit, grace period worker thread will be rescheduled with a sleep delay of one jiffy, between each rescan of the readers, for a grace period phase. srcutree.srcu_retry_check_delay [KNL] Specifies number of microseconds of non-sleeping delay between each non-sleeping poll of readers. srcutree.small_contention_lim [KNL] Specifies the number of update-side contention events per jiffy will be tolerated before initiating a conversion of an srcu_struct structure to big form. Note that the value of srcutree.convert_to_big must have the 0x10 bit set for contention-based conversions to occur. ssbd= [ARM64,HW] Speculative Store Bypass Disable control On CPUs that are vulnerable to the Speculative Store Bypass vulnerability and offer a firmware based mitigation, this parameter indicates how the mitigation should be used: force-on: Unconditionally enable mitigation for for both kernel and userspace force-off: Unconditionally disable mitigation for for both kernel and userspace kernel: Always enable mitigation in the kernel, and offer a prctl interface to allow userspace to register its interest in being mitigated too. stack_guard_gap= [MM] override the default stack gap protection. The value is in page units and it defines how many pages prior to (for stacks growing down) resp. after (for stacks growing up) the main stack are reserved for no other mapping. Default value is 256 pages. stack_depot_disable= [KNL] Setting this to true through kernel command line will disable the stack depot thereby saving the static memory consumed by the stack hash table. By default this is set to false. stacktrace [FTRACE] Enabled the stack tracer on boot up. stacktrace_filter=[function-list] [FTRACE] Limit the functions that the stack tracer will trace at boot up. function-list is a comma-separated list of functions. This list can be changed at run time by the stack_trace_filter file in the debugfs tracing directory. Note, this enables stack tracing and the stacktrace above is not needed. sti= [PARISC,HW] Format: <num> Set the STI (builtin display/keyboard on the HP-PARISC machines) console (graphic card) which should be used as the initial boot-console. See also comment in drivers/video/console/sticore.c. sti_font= [HW] See comment in drivers/video/console/sticore.c. stifb= [HW] Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] strict_sas_size= [X86] Format: <bool> Enable or disable strict sigaltstack size checks against the required signal frame size which depends on the supported FPU features. This can be used to filter out binaries which have not yet been made aware of AT_MINSIGSTKSZ. stress_hpt [PPC] Limits the number of kernel HPT entries in the hash page table to increase the rate of hash page table faults on kernel addresses. stress_slb [PPC] Limits the number of kernel SLB entries, and flushes them frequently to increase the rate of SLB faults on kernel addresses. sunrpc.min_resvport= sunrpc.max_resvport= [NFS,SUNRPC] SunRPC servers often require that client requests originate from a privileged port (i.e. a port in the range 0 < portnr < 1024). An administrator who wishes to reserve some of these ports for other uses may adjust the range that the kernel's sunrpc client considers to be privileged using these two parameters to set the minimum and maximum port values. sunrpc.svc_rpc_per_connection_limit= [NFS,SUNRPC] Limit the number of requests that the server will process in parallel from a single connection. The default value is 0 (no limit). sunrpc.pool_mode= [NFS] Control how the NFS server code allocates CPUs to service thread pools. Depending on how many NICs you have and where their interrupts are bound, this option will affect which CPUs will do NFS serving. Note: this parameter cannot be changed while the NFS server is running. auto the server chooses an appropriate mode automatically using heuristics global a single global pool contains all CPUs percpu one pool for each CPU pernode one pool for each NUMA node (equivalent to global on non-NUMA machines) sunrpc.tcp_slot_table_entries= sunrpc.udp_slot_table_entries= [NFS,SUNRPC] Sets the upper limit on the number of simultaneous RPC calls that can be sent from the client to a server. Increasing these values may allow you to improve throughput, but will also increase the amount of memory reserved for use by the client. suspend.pm_test_delay= [SUSPEND] Sets the number of seconds to remain in a suspend test mode before resuming the system (see /sys/power/pm_test). Only available when CONFIG_PM_DEBUG is set. Default value is 5. svm= [PPC] Format: { on | off | y | n | 1 | 0 } This parameter controls use of the Protected Execution Facility on pSeries. swiotlb= [ARM,IA-64,PPC,MIPS,X86] Format: { <int> [,<int>] | force | noforce } <int> -- Number of I/O TLB slabs <int> -- Second integer after comma. Number of swiotlb areas with their own lock. Will be rounded up to a power of 2. force -- force using of bounce buffers even if they wouldn't be automatically used by the kernel noforce -- Never use bounce buffers (for debugging) switches= [HW,M68k] sysctl.*= [KNL] Set a sysctl parameter, right before loading the init process, as if the value was written to the respective /proc/sys/... file. Both '.' and '/' are recognized as separators. Unrecognized parameters and invalid values are reported in the kernel log. Sysctls registered later by a loaded module cannot be set this way. Example: sysctl.vm.swappiness=40 sysfs.deprecated=0|1 [KNL] Enable/disable old style sysfs layout for old udev on older distributions. When this option is enabled very new udev will not work anymore. When this option is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) in older udev will not work anymore. Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in the kernel configuration. sysrq_always_enabled [KNL] Ignore sysrq setting - this boot parameter will neutralize any effect of /proc/sys/kernel/sysrq. Useful for debugging. tcpmhash_entries= [KNL,NET] Set the number of tcp_metrics_hash slots. Default value is 8192 or 16384 depending on total ram pages. This is used to specify the TCP metrics cache size. See Documentation/networking/ip-sysctl.rst "tcp_no_metrics_save" section for more details. tdfx= [HW,DRM] test_suspend= [SUSPEND] Format: { "mem" | "standby" | "freeze" }[,N] Specify "mem" (for Suspend-to-RAM) or "standby" (for standby suspend) or "freeze" (for suspend type freeze) as the system sleep state during system startup with the optional capability to repeat N number of times. The system is woken from this state using a wakeup-capable RTC alarm. thash_entries= [KNL,NET] Set number of hash buckets for TCP connection thermal.act= [HW,ACPI] -1: disable all active trip points in all thermal zones <degrees C>: override all lowest active trip points thermal.crt= [HW,ACPI] -1: disable all critical trip points in all thermal zones <degrees C>: override all critical trip points thermal.nocrt= [HW,ACPI] Set to disable actions on ACPI thermal zone critical and hot trip points. [HW,ACPI] 1: disable ACPI thermal control thermal.psv= [HW,ACPI] -1: disable all passive trip points <degrees C>: override all passive trip points to this value thermal.tzp= [HW,ACPI] Specify global default ACPI thermal zone polling rate <deci-seconds>: poll all this frequency 0: no polling (default) threadirqs [KNL] Force threading of all interrupt handlers except those marked explicitly IRQF_NO_THREAD. topology= [S390] Format: {off | on} Specify if the kernel should make use of the cpu topology information if the hardware supports this. The scheduler will make use of this information and e.g. base its process migration decisions on it. Default is on. topology_updates= [KNL, PPC, NUMA] Format: {off} Specify if the kernel should ignore (off) topology updates sent by the hypervisor to this LPAR. torture.disable_onoff_at_boot= [KNL] Prevent the CPU-hotplug component of torturing until after init has spawned. torture.ftrace_dump_at_shutdown= [KNL] Dump the ftrace buffer at torture-test shutdown, even if there were no errors. This can be a very costly operation when many torture tests are running concurrently, especially on systems with rotating-rust storage. torture.verbose_sleep_frequency= [KNL] Specifies how many verbose printk()s should be emitted between each sleep. The default of zero disables verbose-printk() sleeping. torture.verbose_sleep_duration= [KNL] Duration of each verbose-printk() sleep in jiffies. tp720= [HW,PS2] tpm_suspend_pcr=[HW,TPM] Format: integer pcr id Specify that at suspend time, the tpm driver should extend the specified pcr with zeros, as a workaround for some chips which fail to flush the last written pcr on TPM_SaveState. This will guarantee that all the other pcrs are saved. tp_printk [FTRACE] Have the tracepoints sent to printk as well as the tracing ring buffer. This is useful for early boot up where the system hangs or reboots and does not give the option for reading the tracing buffer or performing a ftrace_dump_on_oops. To turn off having tracepoints sent to printk, echo 0 > /proc/sys/kernel/tracepoint_printk Note, echoing 1 into this file without the tracepoint_printk kernel cmdline option has no effect. The tp_printk_stop_on_boot (see below) can also be used to stop the printing of events to console at late_initcall_sync. ** CAUTION ** Having tracepoints sent to printk() and activating high frequency tracepoints such as irq or sched, can cause the system to live lock. tp_printk_stop_on_boot [FTRACE] When tp_printk (above) is set, it can cause a lot of noise on the console. It may be useful to only include the printing of events during boot up, as user space may make the system inoperable. This command line option will stop the printing of events to console at the late_initcall_sync() time frame. trace_buf_size=nn[KMG] [FTRACE] will set tracing buffer size on each cpu. trace_clock= [FTRACE] Set the clock used for tracing events at boot up. local - Use the per CPU time stamp counter (converted into nanoseconds). Fast, but depending on the architecture, may not be in sync between CPUs. global - Event time stamps are synchronize across CPUs. May be slower than the local clock, but better for some race conditions. counter - Simple counting of events (1, 2, ..) note, some counts may be skipped due to the infrastructure grabbing the clock more than once per event. uptime - Use jiffies as the time stamp. perf - Use the same clock that perf uses. mono - Use ktime_get_mono_fast_ns() for time stamps. mono_raw - Use ktime_get_raw_fast_ns() for time stamps. boot - Use ktime_get_boot_fast_ns() for time stamps. Architectures may add more clocks. See Documentation/trace/ftrace.rst for more details. trace_event=[event-list] [FTRACE] Set and start specified trace events in order to facilitate early boot debugging. The event-list is a comma-separated list of trace events to enable. See also Documentation/trace/events.rst trace_instance=[instance-info] [FTRACE] Create a ring buffer instance early in boot up. This will be listed in: /sys/kernel/tracing/instances Events can be enabled at the time the instance is created via: trace_instance=<name>,<system1>:<event1>,<system2>:<event2> Note, the "<system*>:" portion is optional if the event is unique. trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall will enable the "sched_switch" event (note, the "sched:" is optional, and the same thing would happen if it was left off). The irq_handler_entry event, and all events under the "initcall" system. trace_options=[option-list] [FTRACE] Enable or disable tracer options at boot. The option-list is a comma delimited list of options that can be enabled or disabled just as if you were to echo the option name into /sys/kernel/tracing/trace_options For example, to enable stacktrace option (to dump the stack trace of each event), add to the command line: trace_options=stacktrace See also Documentation/trace/ftrace.rst "trace options" section. trace_trigger=[trigger-list] [FTRACE] Add a event trigger on specific events. Set a trigger on top of a specific event, with an optional filter. The format is is "trace_trigger=<event>.<trigger>[ if <filter>],..." Where more than one trigger may be specified that are comma deliminated. For example: trace_trigger="sched_switch.stacktrace if prev_state == 2" The above will enable the "stacktrace" trigger on the "sched_switch" event but only trigger it if the "prev_state" of the "sched_switch" event is "2" (TASK_UNINTERUPTIBLE). See also "Event triggers" in Documentation/trace/events.rst traceoff_on_warning [FTRACE] enable this option to disable tracing when a warning is hit. This turns off "tracing_on". Tracing can be enabled again by echoing '1' into the "tracing_on" file located in /sys/kernel/tracing/ This option is useful, as it disables the trace before the WARNING dump is called, which prevents the trace to be filled with content caused by the warning output. This option can also be set at run time via the sysctl option: kernel/traceoff_on_warning transparent_hugepage= [KNL] Format: [always|madvise|never] Can be used to control the default behavior of the system with respect to transparent hugepages. See Documentation/admin-guide/mm/transhuge.rst for more details. trusted.source= [KEYS] Format: <string> This parameter identifies the trust source as a backend for trusted keys implementation. Supported trust sources: - "tpm" - "tee" - "caam" If not specified then it defaults to iterating through the trust source list starting with TPM and assigns the first trust source as a backend which is initialized successfully during iteration. trusted.rng= [KEYS] Format: <string> The RNG used to generate key material for trusted keys. Can be one of: - "kernel" - the same value as trusted.source: "tpm" or "tee" - "default" If not specified, "default" is used. In this case, the RNG's choice is left to each individual trust source. tsc= Disable clocksource stability checks for TSC. Format: <string> [x86] reliable: mark tsc clocksource as reliable, this disables clocksource verification at runtime, as well as the stability checks done at bootup. Used to enable high-resolution timer mode on older hardware, and in virtualized environment. [x86] noirqtime: Do not use TSC to do irq accounting. Used to run time disable IRQ_TIME_ACCOUNTING on any platforms where RDTSC is slow and this accounting can add overhead. [x86] unstable: mark the TSC clocksource as unstable, this marks the TSC unconditionally unstable at bootup and avoids any further wobbles once the TSC watchdog notices. [x86] nowatchdog: disable clocksource watchdog. Used in situations with strict latency requirements (where interruptions from clocksource watchdog are not acceptable). [x86] recalibrate: force recalibration against a HW timer (HPET or PM timer) on systems whose TSC frequency was obtained from HW or FW using either an MSR or CPUID(0x15). Warn if the difference is more than 500 ppm. [x86] watchdog: Use TSC as the watchdog clocksource with which to check other HW timers (HPET or PM timer), but only on systems where TSC has been deemed trustworthy. This will be suppressed by an earlier tsc=nowatchdog and can be overridden by a later tsc=nowatchdog. A console message will flag any such suppression or overriding. tsc_early_khz= [X86] Skip early TSC calibration and use the given value instead. Useful when the early TSC frequency discovery procedure is not reliable, such as on overclocked systems with CPUID.16h support and partial CPUID.15h support. Format: <unsigned int> tsx= [X86] Control Transactional Synchronization Extensions (TSX) feature in Intel processors that support TSX control. This parameter controls the TSX feature. The options are: on - Enable TSX on the system. Although there are mitigations for all known security vulnerabilities, TSX has been known to be an accelerator for several previous speculation-related CVEs, and so there may be unknown security risks associated with leaving it enabled. off - Disable TSX on the system. (Note that this option takes effect only on newer CPUs which are not vulnerable to MDS, i.e., have MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get the new IA32_TSX_CTRL MSR through a microcode update. This new MSR allows for the reliable deactivation of the TSX functionality.) auto - Disable TSX if X86_BUG_TAA is present, otherwise enable TSX on the system. Not specifying this option is equivalent to tsx=off. See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst for more details. tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async Abort (TAA) vulnerability. Similar to Micro-architectural Data Sampling (MDS) certain CPUs that support Transactional Synchronization Extensions (TSX) are vulnerable to an exploit against CPU internal buffers which can forward information to a disclosure gadget under certain conditions. In vulnerable processors, the speculatively forwarded data can be used in a cache side channel attack, to access data to which the attacker does not have direct access. This parameter controls the TAA mitigation. The options are: full - Enable TAA mitigation on vulnerable CPUs if TSX is enabled. full,nosmt - Enable TAA mitigation and disable SMT on vulnerable CPUs. If TSX is disabled, SMT is not disabled because CPU is not vulnerable to cross-thread TAA attacks. off - Unconditionally disable TAA mitigation On MDS-affected machines, tsx_async_abort=off can be prevented by an active MDS mitigation as both vulnerabilities are mitigated with the same mechanism so in order to disable this mitigation, you need to specify mds=off too. Not specifying this option is equivalent to tsx_async_abort=full. On CPUs which are MDS affected and deploy MDS mitigation, TAA mitigation is not required and doesn't provide any additional mitigation. For details see: Documentation/admin-guide/hw-vuln/tsx_async_abort.rst[2|3]= [HW,JOY] TurboGraFX parallel port interface Format: <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> See also Documentation/input/devices/joystick-parport.rst udbg-immortal [PPC] When debugging early kernel crashes that happen after console_init() and before a proper console driver takes over, this boot options might help "seeing" what's going on. uhash_entries= [KNL,NET] Set number of hash buckets for UDP/UDP-Lite connections uhci-hcd.ignore_oc= [USB] Ignore overcurrent events (default N). Some badly-designed motherboards generate lots of bogus events, for ports that aren't wired to anything. Set this parameter to avoid log spamming. Note that genuine overcurrent events won't be reported either. unknown_nmi_panic [X86] Cause panic on unknown NMI. usbcore.authorized_default= [USB] Default USB device authorization: (default -1 = authorized except for wireless USB, 0 = not authorized, 1 = authorized, 2 = authorized if device connected to internal port) usbcore.autosuspend= [USB] The autosuspend time delay (in seconds) used for newly-detected USB devices (default 2). This is the time required before an idle device will be autosuspended. Devices for which the delay is set to a negative value won't be autosuspended at all. usbcore.usbfs_snoop= [USB] Set to log all usbfs traffic (default 0 = off). usbcore.usbfs_snoop_max= [USB] Maximum number of bytes to snoop in each URB (default = 65536). usbcore.blinkenlights= [USB] Set to cycle leds on hubs (default 0 = off). usbcore.old_scheme_first= [USB] Start with the old device initialization scheme (default 0 = off). usbcore.usbfs_memory_mb= [USB] Memory limit (in MB) for buffers allocated by usbfs (default = 16, 0 = max = 2047). usbcore.use_both_schemes= [USB] Try the other device initialization scheme if the first one fails (default 1 = enabled). usbcore.initial_descriptor_timeout= [USB] Specifies timeout for the initial 64-byte USB_REQ_GET_DESCRIPTOR request in milliseconds (default 5000 = 5.0 seconds). usbcore.nousb [USB] Disable the USB subsystem usbcore.quirks= [USB] A list of quirk entries to augment the built-in usb core quirk list. List entries are separated by commas. Each entry has the form VendorID:ProductID:Flags. The IDs are 4-digit hex numbers and Flags is a set of letters. Each letter will change the built-in quirk; setting it if it is clear and clearing it if it is set. The letters have the following meanings: a = USB_QUIRK_STRING_FETCH_255 (string descriptors must not be fetched using a 255-byte read); b = USB_QUIRK_RESET_RESUME (device can't resume correctly so reset it instead); c = USB_QUIRK_NO_SET_INTF (device can't handle Set-Interface requests); d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't handle its Configuration or Interface strings); e = USB_QUIRK_RESET (device can't be reset (e.g morph devices), don't use reset); f = USB_QUIRK_HONOR_BNUMINTERFACES (device has more interface descriptions than the bNumInterfaces count, and can't handle talking to these interfaces); g = USB_QUIRK_DELAY_INIT (device needs a pause during initialization, after we read the device descriptor); h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For high speed and super speed interrupt endpoints, the USB 2.0 and USB 3.0 spec require the interval in microframes (1 microframe = 125 microseconds) to be calculated as interval = 2 ^ (bInterval-1). Devices with this quirk report their bInterval as the result of this calculation instead of the exponent variable used in the calculation); i = USB_QUIRK_DEVICE_QUALIFIER (device can't handle device_qualifier descriptor requests); j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device generates spurious wakeup, ignore remote wakeup capability); k = USB_QUIRK_NO_LPM (device can't handle Link Power Management); l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL (Device reports its bInterval as linear frames instead of the USB 2.0 calculation); m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs to be disconnected before suspend to prevent spurious wakeup); n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a pause after every control message); o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra delay after resetting its port); Example: quirks=0781:5580:bk,0a5c:5834:gij usbhid.mousepoll= [USBHID] The interval which mice are to be polled at. usbhid.jspoll= [USBHID] The interval which joysticks are to be polled at. usbhid.kbpoll= [USBHID] The interval which keyboards are to be polled at. usb-storage.delay_use= [UMS] The delay in seconds before a new device is scanned for Logical Units (default 1). usb-storage.quirks= [UMS] A list of quirks entries to supplement or override the built-in unusual_devs list. List entries are separated by commas. Each entry has the form VID:PID:Flags where VID and PID are Vendor and Product ID values (4-digit hex numbers) and Flags is a set of characters, each corresponding to a common usb-storage quirk flag as follows: a = SANE_SENSE (collect more than 18 bytes of sense data, not on uas); b = BAD_SENSE (don't collect more than 18 bytes of sense data, not on uas); c = FIX_CAPACITY (decrease the reported device capacity by one sector); d = NO_READ_DISC_INFO (don't use READ_DISC_INFO command, not on uas); e = NO_READ_CAPACITY_16 (don't use READ_CAPACITY_16 command); f = NO_REPORT_OPCODES (don't use report opcodes command, uas only); g = MAX_SECTORS_240 (don't transfer more than 240 sectors at a time, uas only); h = CAPACITY_HEURISTICS (decrease the reported device capacity by one sector if the number is odd); i = IGNORE_DEVICE (don't bind to this device); j = NO_REPORT_LUNS (don't use report luns command, uas only); k = NO_SAME (do not use WRITE_SAME, uas only) l = NOT_LOCKABLE (don't try to lock and unlock ejectable media, not on uas); m = MAX_SECTORS_64 (don't transfer more than 64 sectors = 32 KB at a time, not on uas); n = INITIAL_READ10 (force a retry of the initial READ(10) command, not on uas); o = CAPACITY_OK (accept the capacity reported by the device, not on uas); p = WRITE_CACHE (the device cache is ON by default, not on uas); r = IGNORE_RESIDUE (the device reports bogus residue values, not on uas); s = SINGLE_LUN (the device has only one Logical Unit); t = NO_ATA_1X (don't allow ATA(12) and ATA(16) commands, uas only); u = IGNORE_UAS (don't bind to the uas driver); w = NO_WP_DETECT (don't test whether the medium is write-protected). y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE even if the device claims no cache, not on uas) Example: quirks=0419:aaf5:rl,0421:0433:rc user_debug= [KNL,ARM] Format: <int> See arch/arm/Kconfig.debug help text. 1 - undefined instruction events 2 - system calls 4 - invalid data aborts 8 - SIGSEGV faults 16 - SIGBUS faults Example: user_debug=31 userpte= [X86] Flags controlling user PTE allocations. nohigh = do not allocate PTE pages in HIGHMEM regardless of setting of CONFIG_HIGHPTE. vdso= [X86,SH,SPARC] On X86_32, this is an alias for vdso32=. Otherwise: vdso=1: enable VDSO (the default) vdso=0: disable VDSO mapping vdso32= [X86] Control the 32-bit vDSO vdso32=1: enable 32-bit VDSO vdso32=0 or vdso32=2: disable 32-bit VDSO See the help text for CONFIG_COMPAT_VDSO for more details. If CONFIG_COMPAT_VDSO is set, the default is vdso32=0; otherwise, the default is vdso32=1. For compatibility with older kernels, vdso32=2 is an alias for vdso32=0. Try vdso32=0 if you encounter an error that says: dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! vector= [IA-64,SMP] vector=percpu: enable percpu vector domain video= [FB] Frame buffer configuration See Documentation/fb/modedb.rst. video.brightness_switch_enabled= [ACPI] Format: [0|1] If set to 1, on receiving an ACPI notify event generated by hotkey, video driver will adjust brightness level and then send out the event to user space through the allocated input device. If set to 0, video driver will only send out the event without touching backlight brightness level. default: 1 virtio_mmio.device= [VMMIO] Memory mapped virtio (platform) device. <size>@<baseaddr>:<irq>[:<id>] where: <size> := size (can use standard suffixes like K, M and G) <baseaddr> := physical base address <irq> := interrupt number (as passed to request_irq()) <id> := (optional) platform device id example: virtio_mmio.device=1K@0x100b0000:48:7 Can be used multiple times for multiple devices. vga= [BOOT,X86-32] Select a particular video mode See Documentation/x86/boot.rst and Documentation/admin-guide/svga.rst. Use vga=ask for menu. This is actually a boot loader parameter; the value is passed to the kernel using a special protocol. vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. May slow down system boot speed, especially when enabled on systems with a large amount of memory. All options are enabled by default, and this interface is meant to allow for selectively enabling or disabling specific virtual memory debugging features. Available options are: P Enable page structure init time poisoning - Disable all of the above options vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact size of <nn>. This can be used to increase the minimum size (128MB on x86). It can also be used to decrease the size and leave more room for directly mapped kernel RAM. vmcp_cma=nn[MG] [KNL,S390] Sets the memory size reserved for contiguous memory allocations for the vmcp device driver. vmhalt= [KNL,S390] Perform z/VM CP command after system halt. Format: <command> vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. Format: <command> vmpoff= [KNL,S390] Perform z/VM CP command after power off. Format: <command> vsyscall= [X86-64] Controls the behavior of vsyscalls (i.e. calls to fixed addresses of 0xffffffffff600x00 from legacy code). Most statically-linked binaries and older versions of glibc use these calls. Because these functions are at fixed addresses, they make nice targets for exploits that can control RIP. emulate Vsyscalls turn into traps and are emulated reasonably safely. The vsyscall page is readable. xonly [default] Vsyscalls turn into traps and are emulated reasonably safely. The vsyscall page is not readable. none Vsyscalls don't work at all. This makes them quite hard to use for exploits but might break your system. vt.color= [VT] Default text color. Format: 0xYX, X = foreground, Y = background. Default: 0x07 = light gray on black. vt.cur_default= [VT] Default cursor shape. Format: 0xCCBBAA, where AA, BB, and CC are the same as the parameters of the <Esc>[?A;B;Cc escape sequence; see VGA-softcursor.txt. Default: 2 = underline. vt.default_blu= [VT] Format: <blue0>,<blue1>,<blue2>,...,<blue15> Change the default blue palette of the console. This is a 16-member array composed of values ranging from 0-255. vt.default_grn= [VT] Format: <green0>,<green1>,<green2>,...,<green15> Change the default green palette of the console. This is a 16-member array composed of values ranging from 0-255. vt.default_red= [VT] Format: <red0>,<red1>,<red2>,...,<red15> Change the default red palette of the console. This is a 16-member array composed of values ranging from 0-255. vt.default_utf8= [VT] Format=<0|1> Set system-wide default UTF-8 mode for all tty's. Default is 1, i.e. UTF-8 mode is enabled for all newly opened terminals. vt.global_cursor_default= [VT] Format=<-1|0|1> Set system-wide default for whether a cursor is shown on new VTs. Default is -1, i.e. cursors will be created by default unless overridden by individual drivers. 0 will hide cursors, 1 will display them. vt.italic= [VT] Default color for italic text; 0-15. Default: 2 = green. vt.underline= [VT] Default color for underlined text; 0-15. Default: 3 = cyan. watchdog timers [HW,WDT] For information on watchdog timers, see Documentation/watchdog/watchdog-parameters.rst or other driver-specific files in the Documentation/watchdog/ directory. watchdog_thresh= [KNL] Set the hard lockup detector stall duration threshold in seconds. The soft lockup detector threshold is set to twice the value. A value of 0 disables both lockup detectors. Default is 10 seconds. workqueue.watchdog_thresh= If CONFIG_WQ_WATCHDOG is configured, workqueue can warn stall conditions and dump internal state to help debugging. 0 disables workqueue stall detection; otherwise, it's the stall threshold duration in seconds. The default value is 30 and it can be updated at runtime by writing to the corresponding sysfs file. workqueue.disable_numa By default, all work items queued to unbound workqueues are affine to the NUMA nodes they're issued on, which results in better behavior in general. If NUMA affinity needs to be disabled for whatever reason, this option can be used. Note that this also can be controlled per-workqueue for workqueues visible under /sys/bus/workqueue/. workqueue.power_efficient Per-cpu workqueues are generally preferred because they show better performance thanks to cache locality; unfortunately, per-cpu workqueues tend to be more power hungry than unbound workqueues. Enabling this makes the per-cpu workqueues which were observed to contribute significantly to power consumption unbound, leading to measurably lower power usage at the cost of small performance overhead. The default value of this parameter is determined by the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. workqueue.debug_force_rr_cpu Workqueue used to implicitly guarantee that work items queued without explicit CPU specified are put on the local CPU. This guarantee is no longer true and while local CPU is still preferred work items may be put on foreign CPUs. This debug option forces round-robin CPU selection to flush out usages which depend on the now broken guarantee. When enabled, memory and cache locality will be impacted. x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of default x2apic cluster mode on platforms supporting x2apic. xen_512gb_limit [KNL,X86-64,XEN] Restricts the kernel running paravirtualized under Xen to use only up to 512 GB of RAM. The reason to do so is crash analysis tools and Xen tools for doing domain save/restore/migration must be enabled to handle larger domains. xen_emul_unplug= [HW,X86,XEN] Unplug Xen emulated devices Format: [unplug0,][unplug1] ide-disks -- unplug primary master IDE devices aux-ide-disks -- unplug non-primary-master IDE devices nics -- unplug network devices all -- unplug all emulated devices (NICs and IDE disks) unnecessary -- unplugging emulated devices is unnecessary even if the host did not respond to the unplug protocol never -- do not unplug even if version check succeeds xen_legacy_crash [X86,XEN] Crash from Xen panic notifier, without executing late panic() code such as dumping handler. xen_msr_safe= [X86,XEN] Format: <bool> Select whether to always use non-faulting (safe) MSR access functions when running as Xen PV guest. The default value is controlled by CONFIG_XEN_PV_MSR_SAFE. xen_nopvspin [X86,XEN] Disables the qspinlock slowpath using Xen PV optimizations. This parameter is obsoleted by "nopvspin" parameter, which has equivalent effect for XEN platform. xen_nopv [X86] Disables the PV optimizations forcing the HVM guest to run as generic HVM guest with no PV drivers. This option is obsoleted by the "nopv" option, which has equivalent effect for XEN platform. xen_no_vector_callback [KNL,X86,XEN] Disable the vector callback for Xen event channel interrupts. xen_scrub_pages= [XEN] Boolean option to control scrubbing pages before giving them back to Xen, for use by other domains. Can be also changed at runtime with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. xen_timer_slop= [X86-64,XEN] Set the timer slop (in nanoseconds) for the virtual Xen timers (default is 100000). This adjusts the minimum delta of virtualized Xen timers, where lower values improve timer resolution at the expense of processing more timer interrupts. xen.balloon_boot_timeout= [XEN] The time (in seconds) to wait before giving up to boot in case initial ballooning fails to free enough memory. Applies only when running as HVM or PVH guest and started with less memory configured than allowed at max. Default is 180. xen.event_eoi_delay= [XEN] How long to delay EOI handling in case of event storms (jiffies). Default is 10. xen.event_loop_timeout= [XEN] After which time (jiffies) the event handling loop should start to delay EOI handling. Default is 2. xen.fifo_events= [XEN] Boolean parameter to disable using fifo event handling even if available. Normally fifo event handling is preferred over the 2-level event handling, as it is fairer and the number of possible event channels is much higher. Default is on (use fifo events). xirc2ps_cs= [NET,PCMCIA] Format: <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] xive= [PPC] By default on POWER9 and above, the kernel will natively use the XIVE interrupt controller. This option allows the fallback firmware mode to be used: off Fallback to firmware control of XIVE interrupt controller on both pseries and powernv platforms. Only useful on POWER9 and above. [PPC] By default on POWER10 and above, the kernel will use stores for EOI handling when the XIVE interrupt mode is active. This option allows the XIVE driver to use loads instead, as on POWER9. xhci-hcd.quirks [USB,KNL] A hex value specifying bitmask with supplemental xhci host controller quirks. Meaning of each bit can be consulted in header drivers/usb/host/xhci.h. xmon [PPC] Format: { early | on | rw | ro | off } Controls if xmon debugger is enabled. Default is off. Passing only "xmon" is equivalent to "xmon=early". early Call xmon as early as possible on boot; xmon debugger is called from setup_arch(). on xmon debugger hooks will be installed so xmon is only called on a kernel crash. Default mode, i.e. either "ro" or "rw" mode, is controlled with CONFIG_XMON_DEFAULT_RO_MODE. rw xmon debugger hooks will be installed so xmon is called only on a kernel crash, mode is write, meaning SPR registers, memory and, other data can be written using xmon commands. ro same as "rw" option above but SPR registers, memory, and other data can't be written using xmon commands. off xmon is disabled. amd_pstate= [X86] disable Do not enable amd_pstate as the default scaling driver for the supported processors passive Use amd_pstate as a scaling driver, driver requests a desired performance on this abstract scale and the power management firmware translates the requests into actual hardware states (core frequency, data fabric and memory clocks etc.) active Use amd_pstate_epp driver instance as the scaling driver, driver provides a hint to the hardware if software wants to bias toward performance (0x0) or energy efficiency (0xff) to the CPPC firmware. then CPPC power algorithm will calculate the runtime workload and adjust the realtime cores frequency.


Add more DRM drivers.

(Video) Linux Kernel in 19 Minuten erklärt | Linux & Bash Scripting


What are the kernel parameters in Linux? ›

Kernel parameters are tunable values which you can adjust while the system is running. There is no requirement to reboot or recompile the kernel for changes to take effect. It is possible to address the kernel parameters through: The sysctl command.

What is kernel command line in Linux? ›

Kernel command line parameters are parameters that you pass on to the Fatdog64 during the boot process. They are also known as "boot options". Some of these parameters are understood by the Linux kernel, some are understood by Fatdog64 system scripts.

What is the command to list the kernel parameters? ›

The command “modinfo -p ${modulename}” shows a current list of all parameters of a loadable module. Loadable modules, after being loaded into the running kernel, also reveal their parameters in /sys/module/${modulename}/parameters/.

What is kernel boot parameters in Linux? ›

Kernel boot parameters are text strings which are interpreted by the system to change specific behaviors and enable or disable certain features. Kernel boot parameters: are case-sensitive. are sometimes just a simple word ("splash" or "noapic")

What are command-line parameters in Linux? ›

Command-line arguments are parameters that are passed to a script while executing them in the bash shell. They are also known as positional parameters in Linux. We use command-line arguments to denote the position in memory where the command and it's associated parameters are stored.

Where are Linux kernel parameters? ›

Kernel command-line parameters are saved in the boot/grub/grub. cfg configuration file, which is generated by the GRUB2 boot loader. Do not edit this configuration file. Changes to this file are only made by configuration scripts.

What is Linux kernel and how it works? ›

The Linux kernel manages OS resources, making sure there is enough memory available for applications to run, optimizing processor usage, and avoiding system deadlocks caused by competing application demands. The stability of the Linux kernel has made it a key building block for many cloud computing infrastructures.

How to set kernel boot parameters? ›

4 Temporarily modifying kernel boot parameters
  1. Switch on your computer. The boot process will start.
  2. In the GRUB 2 boot screen, highlight the entry you want to modify using the arrow keys ↑ and ↓.
  3. Press the E key. ...
  4. Search for the string splash=silent and remove it.
  5. To boot the entry, press F10 or Ctrl–X.
4 days ago

How to check Linux kernel command-line? ›

To check Linux Kernel version, try the following commands:
  1. uname -r : Find Linux kernel version.
  2. cat /proc/version : Show Linux kernel version with help of a special file.
  3. hostnamectl | grep Kernel : For systemd based Linux distro you can use hotnamectl to display hostname and running Linux kernel version.
Apr 3, 2022

How to check kernel parameters in Linux 7? ›

The sysctl utility (/sbin/sysctl) allows (privileged) users to query and modify kernel parameters during runtime. The utility is common to most Linux distributions, however, subtle differences may exist between distributions e.g. RHEL/OL and SuSE.

How to check parameters in Linux? ›

How to view Linux kernel parameters using /proc/cmdline. The above entry from /proc/cmdline file shows the parameters passed to the kernel at the time it is started. I booted my Linux server using /boot/vmlinuz-4.15. 0-42-generic kernel image.

How to check sysctl parameters in Linux? ›

You need to use the sysctl command, which is used to modify kernel parameters at runtime. The parameters available are those listed under /proc/sys/. Procfs is required for sysctl support in Linux. You can use the sysctl command to both read and write sysctl variables.

How to change kernel command-line parameters? ›

Changing kernel command-line parameters temporarily at boot time. Make temporary changes to a Kernel Menu Entry by changing the kernel parameters only during a single boot process. Select the kernel you want to start when the GRUB 2 boot menu appears and press the e key to edit the kernel parameters.

How does the Linux kernel boot? ›

Thus, the kernel initializes devices, mounts the root filesystem specified by the boot loader as read only, and runs Init ( /sbin/init ) which is designated as the first process run by the system (PID = 1). A message is printed by the kernel upon mounting the file system, and by Init upon starting the Init process.

What are parameters in operating system? ›

System parameters define either server or client properties. Other parameters do not have a value unless a system administrator sets one. For example, the system parameter determines the port that clients use to access the Service Manager server.

What are command line parameters? ›

Command-line arguments are simple parameters that are given on the system's command line, and the values of these arguments are passed on to your program during program execution. When a program starts execution without user interaction, command-line arguments are used to pass values or files to it.

What is the use of command line parameter? ›

The program name will be stored in the first item in argv, followed by each of the parameters. Hence, if the program name is followed by n parameters there will be n + 1 entries in argv, ranging from argv[0] to argv[n]. Furthermore, argc will be automatically set equal to n + 1.

What is a command parameter? ›

The CommandParameter property is used to pass specific information to the command when it is executed. The type of the data is defined by the command. Many commands do not expect command parameters; for these commands, any command parameters passed will be ignored.

Where is Linux kernel main function? ›

The Linux® kernel is the main component of a Linux operating system (OS) and is the core interface between a computer's hardware and its processes. It communicates between the 2, managing resources as efficiently as possible.

What are the functions of Linux kernel? ›

The main roles of the Linux kernel are as follows: It provides a set of portable hardware and architecture APIs that offer user space applications the possibility to use necessary hardware resources. It helps with the management of hardware resources, such as a CPU, input/output peripherals, and memory.

What does the Linux kernel contain? ›

2.2. Important parts of the kernel. The Linux kernel consists of several important parts: process management, memory management, hardware device drivers, filesystem drivers, network management, and various other bits and pieces.

What is Linux basic kernel structure? ›

The Linux kernel is one layer in the architecture of the entire Linux system. The kernel is conceptually composed of five major subsystems: the process scheduler, the memory manager, the virtual file system, the network interface, and the inter-process communication interface.

How to set the kernel parameters in Linux? ›

Enter the command /sbin/sysctl -a to confirm that the values are set correctly. After updating the values of the kernel parameters in the /etc/sysctl. conf file, either restart the computer, or run the command sysctl -p to make the changes in the /etc/sysctl. conf file available in the active kernel memory.

How to add a Linux kernel parameter? ›

How to set temporary kernel boot parameters
  1. Reboot your system and hold the Shift key as its first booting up, and you will be brough into the GRUB boot menu. ...
  2. Highlight the kernel you want to edit (probably the first selection in the menu) and press e on your keyboard to temporarily edit the boot parameters.
Mar 28, 2022

How do I set the default Linux kernel? ›

Change to a different default kernel by running the grubby --set-default command with the specific kernel that you choose to run after rebooting.

How many lines is the Linux kernel? ›

The Linux kernel, at over 8 million lines of code and well over 1000 contributors to each release, is one of the largest and most active free software projects in existence.

How do I find kernel configuration? ›

The Linux kernel configuration is usually found in the kernel source in the file: /usr/src/linux/. config . It is not recommended to edit this file directly but to use one of these configuration options: make config - starts a character based questions and answer session.

How do I run a Linux command line? ›

Run Linux tools from a Windows command line

Run Linux binaries from the Windows Command Prompt (CMD) or PowerShell using wsl <command> (or wsl.exe <command> ). Binaries invoked in this way: Use the same working directory as the current CMD or PowerShell prompt. Run as the WSL default user.

What are kernel parameters and why to set them? ›

Kernel parameters can be set either temporarily by editing the boot entry in the boot loader's boot selection menu, or permanently by modifying the boot loader's configuration file. The following examples add the quiet and splash parameters to Syslinux, systemd-boot, GRUB, GRUB Legacy, LILO, and rEFInd.

How to set kernel parameters in Linux for Oracle 19c? ›

  1. If you used the Oracle Database Preinstallation RPM, then your kernel parameter settings reside in the /etc/sysctl. d/99-oracle-database-server-19c-preinstall-sysctl. ...
  2. Include lines only for the kernel parameter values to change. ...
  3. The /etc/sysctl. ...
  4. Avoid setting kernel parameter values in multiple files under /etc/sysctl.

Why sysctl is used in Linux? ›

The sysctl command is used to list, read, and set kernel tunables. It can filter tunables when listing or reading and set tunables temporarily or permanently.

How to update Linux kernel command line? ›

Option A: Use the System Update Process
  1. Step 1: Check Your Current Kernel Version. At a terminal window, type: uname –sr. ...
  2. Step 2: Update the Repositories. At a terminal, type: sudo apt-get update. ...
  3. Step 3: Run the upgrade. While still in the terminal, type: sudo apt-get dist-upgrade.

How do I change kernel settings? ›

To configure the kernel, change to /usr/src/linux and enter the command make config. Choose the features you want supported by the kernel. Usually, There are two or three options: y, n, or m. m means that this device will not be compiled directly into the kernel, but loaded as a module.

What are the different types of module parameter in kernel? ›

First, module parameters can have a number of different types such as int, uint, short, ushort, long, bool and a few others, all defined in the header file <linux/moduleparam.

What are the 4 stages of the boot process? ›

is a process of switching on the computer and starting the operating system. Six steps of the booting process are BIOS and Setup Program, The Power- On-Self-Test (POST), The Operating system Loads, System Configuration, System Utility Loads and Users Authentication.

What is the first kernel process? ›

When the kernel has started itself (has been loaded into memory, has started running, and has initialized all device drivers and data structures and such), it finishes its own part of the boot process by starting a user level program, init. Thus, init is always the first process (its process number is always 1).

What are the four steps of the Linux boot process? ›

The Linux boot process can be broken down in 4 simple stages:
  • BIOS. The BIOS (stands for "Basic Input/Output System") initializes the hardware and makes sure with a Power-on self test (POST) that all the hardware is good to go. ...
  • Bootloader. ...
  • Kernel. ...
  • Init.

What are the four types of parameters? ›

Supported parameter types are string, integer, Boolean, and array.

What are the basic parameters? ›

basic parameters means any regulatory, technical or meet the relevant essential requirements.

What are the three kinds of parameters? ›

What are different types of parameters to a method in C#?
  • Value Parameters.
  • Reference Parameters.
  • Output Parameters.
Aug 4, 2020

What are the 5 components of an OS kernel? ›

Every part which is to be accessed by most programs which cannot be put in a library is in the kernel space: Device drivers, scheduler, memory handling, file systems, and network stacks.

How to pass kernel parameters in Linux? ›

Kernel parameters can be set either temporarily by editing the boot entry in the boot loader's boot selection menu, or permanently by modifying the boot loader's configuration file. The following examples add the quiet and splash parameters to Syslinux, systemd-boot, GRUB, GRUB Legacy, LILO, and rEFInd.

What is Linux kernel and its functions? ›

The Linux® kernel is the main component of a Linux operating system (OS) and is the core interface between a computer's hardware and its processes. It communicates between the 2, managing resources as efficiently as possible.

What is Linux kernel and its features? ›

The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU operating system, which was written to be a free (libre) replacement for Unix.

How many kernels are there in Linux? ›

It has five types, namely, monolithic kernel, microkernel, hybrid kernel, nano kernel, and exo kernel. The functions of a kernel include accessing computer resources, memory management, device management, and resource management.

What are different types of Linux kernel? ›

The five main types of kernels are:
  • Monolithic Kernel.
  • Microkernel.
  • Hybrid Kernel.
  • Nano Kernel.
  • Exo Kernel.
Feb 17, 2023

What are the types of parameters in functions? ›

Formal parameters and actual parameters

According to the example above, the formal parameters are a and b , and the *actual *parameters are x and y . Essentially, the variables being passed in the function call are actual parameters, and the variables being initialized and used in the function are formal* *parameters.

How to check OS kernel parameters in Linux? ›

How to view Linux kernel parameters using /proc/cmdline. The above entry from /proc/cmdline file shows the parameters passed to the kernel at the time it is started. I booted my Linux server using /boot/vmlinuz-4.15. 0-42-generic kernel image.

How to find kernel command line? ›

Commands to find your Linux Kernel Version
  1. uname -r : Find Linux kernel version.
  2. cat /proc/version : Show Linux kernel version with help of a special file.
  3. hostnamectl | grep Kernel : For systemd based Linux distro you can use hotnamectl to display hostname and running Linux kernel version.
Apr 3, 2022

What are main features of kernel? ›

In broad terms, an OS kernel performs three primary jobs. It provides the interfaces needed for users and applications to interact with the computer. It launches and manages applications. It manages the underlying system hardware devices.

What is the structure of kernel? ›

Kernel Components

The kernel stores and organizes a lot of information. So it has data about which processes are running in the system, their memory requirements, files in use etc. To handle all this, three important structures are used. These are process table, file table and v node/ i node information.


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