Kernel Parameters                          ~~~~~~~~~~~~~~~~~ The following is a consolidated list of the kernel parameters as implemented(mostly) by the __setup() macro and sorted into English Dictionary order(defined as ignoring all punctuation and sorting digits before letters in acase insensitive manner), and with descriptions where known. Module parameters for loadable modules are specified only as theparameter name with optional '=' and value as appropriate, such as: 	modprobe usbcore blinkenlights=1 Module parameters for modules that are built into the kernel imageare specified on the kernel command line with the module name plus'.' plus parameter name, with '=' and value if appropriate, such as: 	usbcore.blinkenlights=1 Hyphens (dashes) and underscores are equivalent in parameter names, so	log_buf_len=1M print-fatal-signals=1can also be entered as	log-buf-len=1M print_fatal_signals=1  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 command"echo -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.	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 bootloader, and have no meaning to the kernel directly.Do not modify the syntax of boot loader parameters without extremeneed or coordination with <Documentation/x86/boot.txt>. There are also arch-specific kernel-parameters not documented here.See for example <Documentation/x86/x86_64/boot-options.txt>. 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/asm/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', equalling 2^10, 2^20, and 2^30bytes 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: <int>			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: <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_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_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_no_auto_ssdt	[HW,ACPI] Disable automatic loading of SSDT 	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_serialize	[HW,ACPI] force serialization of AML methods 	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. 	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: <a>,<b>			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: <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,X86-32] 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: <io>,<irq>,<nodeID> 	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 	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. 	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

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