Kernel Parameters ~~~~~~~~~~~~~~~~~ The following is a consolidated list of the kernel parameters as implemented by the __setup(), core_param() and module_param() macros and sorted into English Dictionary order (defined as ignoring all punctuation and sorting digits before letters in a case insensitive manner), 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 '.', the parameter gets passed to init: parameters with '=' go into init's environment, 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 command line 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 be specified on the kernel command line. modprobe looks through the kernel command line (/proc/cmdline) and collects module parameters when it loads a module, so the kernel command line can be used for loadable modules too. Hyphens (dashes) and underscores are equivalent in parameter names, so log_buf_len=1M print-fatal-signals=1 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" This document may not be entirely up to date and comprehensive. The command "modinfo -p ${modulename}" shows a current list of all parameters of a loadable module. Loadable modules, after being loaded into the running kernel, also reveal their parameters in /sys/module/${modulename}/parameters/. Some of these parameters may be changed at runtime by the command "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". The parameters listed below are only valid if certain kernel build options were enabled and if respective hardware is present. The text in square brackets at the beginning of each description states the restrictions within which a parameter 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. ARM ARM architecture is enabled. AVR32 AVR32 architecture is enabled. AX25 Appropriate AX.25 support is enabled. BLACKFIN Blackfin architecture 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 runtime EDD BIOS Enhanced Disk Drive Services (EDD) is enabled EFI EFI Partitioning (GPT) is enabled EIDE EIDE/ATAPI support is enabled. EVM Extended Verification Module FB The frame buffer device is enabled. FTRACE Function tracing enabled. GCOV GCOV profiling is enabled. HW Appropriate hardware is enabled. IA-64 IA-64 architecture is enabled. IMA Integrity measurement architecture is enabled. IOSCHED More than one I/O scheduler 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. JOY Appropriate joystick support is enabled. KGDB Kernel debugger support is enabled. KVM Kernel Virtual Machine support is enabled. LIBATA Libata driver is enabled LP 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.txt. 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. OSS OSS sound support is enabled. PV_OPS A paravirtualized kernel is enabled. PARIDE The ParIDE (parallel port IDE) subsystem 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. 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. APPARMOR AppArmor 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. TS Appropriate touchscreen support is 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. XT IBM PC/XT MFM hard disk 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.txt . X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) XEN Xen support is enabled 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 boot loader, and have no meaning to the kernel directly. Do not modify the syntax of boot loader parameters without extreme need or coordination with . There are also arch-specific kernel-parameters not documented here. See for example . Note that ALL kernel parameters listed below are CASE SENSITIVE, and that a trailing = on the name of any parameter states that that parameter will be entered as an environment variable, whereas its absence indicates that it will appear as a kernel argument readable via /proc/cmdline by programs running once the system is up. The number of kernel parameters is not limited, but the length of the complete command line (parameters including spaces etc.) is limited to a fixed number of characters. This limit depends on the architecture and is between 256 and 4096 characters. It is defined in the file ./include/asm/setup.h as COMMAND_LINE_SIZE. Finally, the [KMG] suffix is commonly described after a number of kernel parameter values. These 'K', 'M', and 'G' letters represent the _binary_ multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 bytes respectively. Such letter suffixes can also be entirely omitted. acpi= [HW,ACPI,X86] Advanced Configuration and Power Interface Format: { force | off | strict | noirq | rsdt } force -- enable ACPI if default was off 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 See also Documentation/power/runtime_pm.txt, pci=noacpi 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_apic_instance= [ACPI, IOAPIC] Format: 2: use 2nd APIC table, if available 1,0: use 1st APIC table default: 0 acpi_backlight= [HW,ACPI] acpi_backlight=vendor acpi_backlight=video If set to vendor, prefer vendor specific driver (e.g. thinkpad_acpi, sony_acpi, etc.) instead of the ACPI video.ko driver. acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] acpi.debug_level= [HW,ACPI,ACPI_DEBUG] Format: 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_PCI_COMPONENT 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/acpi/debug.txt for more information about debug layers and levels. Enable processor driver info messages: acpi.debug_layer=0x20000000 Enable PCI/PCI interrupt routing info messages: acpi.debug_layer=0x400000 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_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: ,... acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for use by PCI Format: ,... 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_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. 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_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS Format: To spoof as Windows 98: ="Microsoft Windows" 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= # 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_nohwsig, old_ordering, nonvs, sci_force_enable } See Documentation/power/video.txt 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_nohwsig prevents ACPI hardware signature from being used during resume from hibernation. 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). 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 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_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump kernels. 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/alsa-parameters.txt 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. amd_iommu= [HW,X86-64] Pass parameters to the AMD IOMMU driver in the system. Possible values are: fullflush - enable flushing of IO/TLB entries when they are unmapped. Otherwise they are flushed before they will be reused, which is a lot of faster 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 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. amijoy.map= [HW,JOY] Amiga joystick support Map of devices attached to JOY0DAT and JOY1DAT Format: , See also Documentation/input/joystick.txt analog.map= [HW,JOY] Analog joystick and gamepad support Specifies type or capabilities of an analog joystick connected to one of 16 gameports Format: ,,.. 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,X86-32] Advanced Programmable Interrupt Controller Change the output verbosity whilst booting Format: { quiet (default) | verbose | debug } Change the amount of debugging information output when initialising the APIC and IO-APIC components. autoconf= [IPV6] See Documentation/networking/ipv6.txt. 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 apm= [APM] Advanced Power Management See header of arch/x86/kernel/apm_32.c. arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards Format: ,, 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: (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: (0 = real, 1 = synthetic (default)) atkbd.softrepeat= [HW] Use software keyboard repeat audit= [KNL] Enable the audit sub-system Format: { "0" | "1" } (0 = disabled, 1 = enabled) 0 - 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 - 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: (must be >=0) Default: 64 baycom_epp= [HW,AX25] Format: , baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem Format: , See header of drivers/net/hamradio/baycom_par.c. baycom_ser_fdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Full Duplex Mode) Format: ,,[,] 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: ,, See header of drivers/net/hamradio/baycom_ser_hdx.c. blkdevparts= Manual partition parsing of block device(s) for embedded devices based on command line input. See Documentation/block/cmdline-partition.txt boot_delay= Milliseconds to delay each printk during boot. Values larger than 10 seconds (10000) are changed to no delay (0). Format: integer bootmem_debug [KNL] Enable bootmem allocator debug messages. bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) bttv.radio= Most important insmod options are available as kernel args too. bttv.pll= See Documentation/video4linux/bttv/Insmod-options 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. ca_keys= [KEYS] This parameter identifies a specific key(s) on the system trusted keyring to be used for certificate trust validation. format: { id: | 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/CommonIO for details. cgroup_disable= [KNL] Disable a particular controller Format: {name of the controller(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 {Currently only "memory" controller deal with this and cut the overhead, others just disable the usage. So only cgroup_disable=memory is actually worthy} 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 /selinux/checkreqprot. cio_ignore= [S390] See Documentation/s390/CommonIO for details. 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/clk.txt. 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: 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 [AVR32] avr32 [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 clearcpuid=BITNUM [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeature.h for the valid bit numbers. Note the Linux specific bits are not necessarily stable over kernel options, but the vendor specific ones should be. 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. cma=nn[MG]@[start[MG][-end[MG]]] [ARM,X86,KNL] 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 include/linux/dma-contiguous.h 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. code_bytes [X86] How many bytes of object code to print in an oops report. Range: 0 - 8192 Default: 64 com20020= [HW,NET] ARCnet - COM20020 chipset Format: [,[,[,[,[,]]]]] com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) Format: [,] com90xx= [HW,NET] ARCnet - COM90xx chipset (memory-mapped buffers) Format: [,[,]] condev= [HW,S390] console device conmode= console= [KNL] Output console device and options. tty Use the virtual console device . ttyS[,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/serial-console.txt for more information. See Documentation/networking/netconsole.txt for an alternative. uart[8250],io,[,options] uart[8250],mmio,[,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. The options are the same as for ttyS, above. hvc Use the hypervisor console device . This is for both Xen and PowerPC hypervisors. 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. consoleblank= [KNL] The console blank (screen saver) timeout in seconds. Defaults to 10*60 = 10mins. A value of 0 disables the blank timer. coredump_filter= [KNL] Change the default value for /proc//coredump_filter. See also Documentation/filesystems/proc.txt. cpuidle.off=1 [CPU_IDLE] disable the cpuidle sub-system cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver Format: ,,,[,] 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. Check Documentation/kdump/kdump.txt 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/kdump/kdump.txt for an example. crashkernel=size[KMG],high [KNL, x86_64] 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] 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. Kernel would try to allocate 72M below 4G automatically. This one let user to 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. cs89x0_dma= [HW,NET] Format: cs89x0_media= [HW,NET] Format: { rj45 | aui | bnc } dasd= [HW,NET] See header of drivers/s390/block/dasd_devmap.c. db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port (one device per port) Format: , See also Documentation/input/joystick-parport.txt ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot time. See Documentation/dynamic-debug-howto.txt for details. Deprecated, see dyndbg. debug [KNL] Enable kernel debugging (events log level). debug_locks_verbose= [KNL] verbose self-tests Format=<0|1> Print debugging info while doing the locking API self-tests. We default to 0 (no extra messages), setting it to 1 will print _a lot_ more information - normally only useful to kernel 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 programing 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. debugpat [X86] Enable PAT debugging decnet.addr= [HW,NET] Format: [,] See also Documentation/networking/decnet.txt. default_hugepagesz= [same as hugepagesz=] The size of the default HugeTLB page size. This is the size represented by the legacy /proc/ hugepages APIs, used for SHM, and default size when mounting hugetlbfs filesystems. Defaults to the default architecture's huge page size if not specified. dhash_entries= [KNL] Set number of hash buckets for dentry cache. disable= [IPV6] See Documentation/networking/ipv6.txt. disable_cpu_apicid= [X86,APIC,SMP] Format: 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 if to workaround buggy firmware. disable_ipv6= [IPV6] See Documentation/networking/ipv6.txt. 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. dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, this option disables the debugging code at boot. dma_debug_entries= 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= 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. drm_kms_helper.edid_firmware=[:] Broken monitors, graphic adapters and KVMs may send no or incorrect EDID data sets. This parameter allows to specify an EDID data set in the /lib/firmware directory that is 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/EDID/HOWTO.txt. An EDID data set will only be used for a particular connector, if its name and a colon are prepended to the EDID name. dscc4.setup= [NET] dyndbg[="val"] [KNL,DYNAMIC_DEBUG] module.dyndbg[="val"] Enable debug messages at boot time. See Documentation/dynamic-debug-howto.txt 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. cdns, Start an early, polled-mode console on a cadence serial port at the specified address. The cadence serial port must already be setup and configured. Options are not yet supported. uart[8250],io,[,options] uart[8250],mmio,[,options] uart[8250],mmio32,[,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). The options are the same as for ttyS, above. pl011, 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. msm_serial, 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, 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. smh Use ARM semihosting calls for early console. earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] earlyprintk=vga earlyprintk=efi earlyprintk=xen earlyprintk=serial[,ttySn[,baudrate]] earlyprintk=serial[,0x...[,baudrate]] earlyprintk=ttySn[,baudrate] earlyprintk=dbgp[debugController#] 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, efi, 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 and EFI output is eventually overwritten by the real console. The xen output can only be used by Xen PV guests. 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. ekgdboc= [X86,KGDB] Allow early kernel console debugging ekgdboc=kbd This is designed to be used in conjunction with the boot argument: earlyprintk=vga edd= [EDD] Format: {"off" | "on" | "skip[mbr]"} efi= [EFI] Format: { "old_map", "nochunk", "noruntime" } old_map [X86-64]: switch to the old ioremap-based EFI runtime services mapping. 32-bit still uses this one by default. 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 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. eisa_irq_edge= [PARISC,HW] See header of drivers/parisc/eisa.c. elanfreq= [X86-32] See comment before function elanfreq_setup() in arch/x86/kernel/cpu/cpufreq/elanfreq.c. elevator= [IOSCHED] Format: {"cfq" | "deadline" | "noop"} See Documentation/block/cfq-iosched.txt and Documentation/block/deadline-iosched.txt for details. 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/kdump/kdump.txt 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 /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. failslab= fail_page_alloc= fail_make_request=[KNL] General fault injection mechanism. Format: ,,, See also Documentation/fault-injection/. floppy= [HW] See Documentation/blockdev/floppy.txt. 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_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. gamecon.map[2|3]= [HW,JOY] Multisystem joystick and NES/SNES/PSX pad support via parallel port (up to 5 devices per port) Format: ,,,,, See also Documentation/input/joystick-parport.txt 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. 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 grcan.select= [HW] Select which physical interface to use. Format: 0 | 1 Default: 0 grcan.txsize= [HW] Sets the size of the tx buffer. Format: such that (txsize & ~0x1fffc0) == 0. Default: 1024 grcan.rxsize= [HW] Sets the size of the rx buffer. Format: such that (rxsize & ~0x1fffc0) == 0. Default: 1024 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: ,, hest_disable [ACPI] Disable Hardware Error Source Table (HEST) support; corresponding firmware-first mode error processing logic will be disabled. highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact size of . 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" hisax= [HW,ISDN] See Documentation/isdn/README.HiSax. hlt [BUGS=ARM,SH] 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,X86-32,IA-64] HugeTLB pages to allocate at boot. hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. On x86-64 and powerpc, this option can be specified multiple times interleaved with hugepages= to reserve huge pages of different sizes. Valid pages sizes on x86-64 are 2M (when the CPU supports "pse") and 1G (when the CPU supports the "pdpe1gb" cpuinfo flag) Note that 1GB pages can only be allocated at boot time using hugepages= and not freed afterwards. 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. hwthread_map= [METAG] Comma-separated list of Linux cpu id to hardware thread id mappings. Format: : 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. 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: , i8042.debug [HW] Toggle i8042 debug mode i8042.direct [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 and cleanup i8042.unlock [HW] Unlock (ignore) the keylock i810= [HW,DRM] i8k.ignore_dmi [HW] Continue probing hardware even if DMI data indicates that the driver is running on unsupported hardware. i8k.force [HW] Activate i8k driver even if SMM BIOS signature does not match list of supported models. i8k.power_status [HW] Report power status in /proc/i8k (disabled by default) i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN capability is set. 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: [,[,[,]]] ide-core.nodma= [HW] (E)IDE subsystem Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr .cdrom .chs .ignore_cable are additional options See Documentation/ide/ide.txt. ide-generic.probe-mask= [HW] (E)IDE subsystem Format: Probe mask for legacy ISA IDE ports. Depending on platform up to 6 ports are supported, enabled by setting corresponding bits in the mask to 1. The default value is 0x0, which has a special meaning. On systems that have PCI, it triggers scanning the PCI bus for the first and the second port, which are then probed. On systems without PCI the value of 0x0 enables probing the two first ports as if it was 0x3. ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem Claim all unknown PCI IDE storage controllers. 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 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. 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] The builtin appraise policy appraises all files owned by uid=0. 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_tcb [IMA] 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" } Default: "ima-ng" ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage Format: 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: 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: 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. initrd= [BOOT] Specify the location of the initial ramdisk inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver Format: 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. forcedac [x86_64] With this option iommu will not optimize to look for io virtual address below 32-bit forcing dual address cycle on pci bus for cards supporting greater than 32-bit addressing. The default is to look for translation below 32-bit and if not available then look in the higher range. strict [Default Off] With this option on every unmap_single operation will result in a hardware IOTLB flush operation as opposed to batching them for performance. 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. intel_idle.max_cstate= [KNL,HW,ACPI,X86] 0 disables intel_idle and fall back on acpi_idle. 1 to 6 specify maximum depth of C-state. intel_pstate= [X86] disable Do not enable intel_pstate as the default scaling driver for the supported processors 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 iomem= Disable strict checking of access to MMIO memory strict regions from userspace. relaxed iommu= [x86] off force noforce biomerge panic nopanic merge nomerge forcesac soft pt [x86, IA-64] 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/filesystems/nfs/nfsroot.txt. 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: ,,, isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. Format: ,..., or - (must be a positive range in ascending order) or a mixture ,...,- This option can be used to specify one or more CPUs to isolate from the general SMP balancing and scheduling algorithms. You can move a process onto or off an "isolated" CPU via the CPU affinity syscalls or cpuset. begins at 0 and the maximum value is "number of CPUs in system - 1". This option is the preferred way to isolate CPUs. The alternative -- manually setting the CPU mask of all tasks in the system -- can cause problems and suboptimal load balancer performance. iucv= [HW,NET] ivrs_ioapic [HW,X86_64] Provide an override to the IOAPIC-ID<->DEVICE-ID mapping provided in the IVRS ACPI table. For example, to map IOAPIC-ID decimal 10 to PCI device 00:14.0 write the parameter as: ivrs_ioapic[10]=00:14.0 ivrs_hpet [HW,X86_64] Provide an override to the HPET-ID<->DEVICE-ID mapping provided in the IVRS ACPI table. For example, to map HPET-ID decimal 0 to PCI device 00:14.0 write the parameter as: ivrs_hpet[0]=00:14.0 js= [HW,JOY] Analog joystick See Documentation/input/joystick.txt. kaslr/nokaslr [X86] Enable/disable kernel and module base offset ASLR (Address Space Layout Randomization) if built into the kernel. When CONFIG_HIBERNATION is selected, kASLR is disabled by default. When kASLR is enabled, hibernation will be disabled. keepinitrd [HW,ARM] kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] 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. The remaining memory in each node is used for Movable pages. In the event, a node is too small to have both kernelcore and Movable pages, kernelcore pages will take priority and other nodes will have a larger number of Movable pages. The Movable zone is used for the allocation of pages that may be reclaimed or moved by the page migration subsystem. This means that HugeTLB pages may not be allocated from this zone. Note that allocations like PTEs-from-HighMem still use the HighMem zone if it exists, and the Normal zone if it does not. kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. Format: [,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: [,baud] keyboard only format: kbd keyboard and serial format: kbd,[,baud] Optional Kernel mode setting: kms, kbd format: kms,kbd kms, kbd and serial format: kms,kbd,[,baud] 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. kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode Valid arguments: 0, 1, 2 kmemcheck=0 (disabled) kmemcheck=1 (enabled) kmemcheck=2 (one-shot mode) Default: 2 (one-shot mode) kstack=N [X86] Print N words from the kernel stack in oops dumps. kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. Default is 0 (don't ignore, but inject #GP) kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit KVM MMU at runtime. Default is 0 (off) 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-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] Enable emulation of invalid guest states Default is 0 (disabled) 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.vpid= [KVM,Intel] Disable Virtual Processor Identification feature (tagged TLBs) on capable Intel chips. Default is 1 (enabled) l2cr= [PPC] l3cr= [PPC] lapic [X86-32,APIC] Enable the local APIC even if BIOS disabled it. lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline value for LAPIC timer one-shot implementation. Default back to the programmable timer unit in the LAPIC. 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: libata.force= [LIBATA] Force configurations. The format is 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's 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. * [no]ncq: Turn on or off NCQ. * nohrst, nosrst, norst: suppress hard, soft and both resets. * rstonce: only attempt one reset during hot-unplug link recovery * dump_id: dump IDENTIFY data. * atapi_dmadir: Enable ATAPI DMADIR bridge support * disable: Disable this device. If there are multiple matching configurations changing the same attribute, the last one is used. memblock=debug [KNL] Enable memblock debug messages. load_ramdisk= [RAM] List of ramdisks to load from floppy See Documentation/blockdev/ramdisk.txt. lockd.nlm_grace_period=P [NFS] Assign grace period. Format: lockd.nlm_tcpport=N [NFS] Assign TCP port. Format: lockd.nlm_timeout=T [NFS] Assign timeout value. Format: lockd.nlm_udpport=M [NFS] Assign UDP port. Format: 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_runnable= [BOOT] Start locktorture running at boot time. 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: 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