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 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.	ALSA	ALSA sound support is enabled.	APIC	APIC support is enabled.	APM	Advanced Power Management support is enabled.	AX25	Appropriate AX.25 support is enabled.	CD	Appropriate CD support is enabled.	DRM	Direct Rendering Management support is enabled.	EDD	BIOS Enhanced Disk Drive Services (EDD) is enabled	EFI	EFI Partitioning (GPT) is enabled	EIDE	EIDE/ATAPI support is enabled.	FB	The frame buffer device is enabled.	HW	Appropriate hardware is enabled.	IA-32	IA-32 aka i386 architecture is enabled.	IA-64	IA-64 architecture is enabled.	IOSCHED	More than one I/O scheduler is enabled.	IP_PNP	IP DHCP, BOOTP, or RARP is enabled.	ISAPNP	ISA PnP code is enabled.	ISDN	Appropriate ISDN support is enabled.	JOY	Appropriate joystick 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.	MCA	MCA bus support is enabled.	MDA	MDA console support is enabled.	MOUSE	Appropriate mouse support is enabled.	MSI	Message Signaled Interrupts (PCI).	MTD	MTD support is enabled.	NET	Appropriate network support is enabled.	NUMA	NUMA support is enabled.	GENERIC_TIME The generic timeofday code is enabled.	NFS	Appropriate NFS support is enabled.	OSS	OSS sound support is enabled.	PARIDE	The ParIDE subsystem is enabled.	PARISC	The PA-RISC architecture is enabled.	PCI	PCI bus 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 has their options described inside of			Documentation/scsi/.	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 is enabled.	TS	Appropriate touchscreen support is enabled.	USB	USB support is enabled.	USBHID	USB Human Interface Device support is enabled.	V4L	Video For Linux support 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.	X86-64	X86-64 architecture is enabled.			More X86-64 boot options can be found in			Documentation/x86_64/boot-options.txt . 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/i386/boot.txt>. There are also arch-specific kernel-parameters not documented here.See for example <Documentation/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.  	53c7xx=		[HW,SCSI] Amiga SCSI controllers			See header of drivers/scsi/53c7xx.c.			See also Documentation/scsi/ncr53c7xx.txt. 	acpi=		[HW,ACPI,X86-64,i386]			Advanced Configuration and Power Interface			Format: { force | off | ht | strict | noirq }			force -- enable ACPI if default was off			off -- disable ACPI if default was on			noirq -- do not use ACPI for IRQ routing			ht -- run only enough ACPI to enable Hyper Threading			strict -- Be less tolerant of platforms that are not				strictly ACPI specification compliant. 			See also Documentation/pm.txt, 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_sleep=	[HW,ACPI] Sleep options			Format: { s3_bios, s3_mode }			See Documentation/power/video.txt 	acpi_sci=	[HW,ACPI] ACPI System Control Interrupt trigger mode			Format: { level | edge | high | low } 	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_pci=	[HW,ACPI] If irq_balance, clear listed IRQs for			use by PCI			Format: <irq>,<irq>... 	acpi_irq_isa=	[HW,ACPI] If irq_balance, mark listed IRQs used by ISA			Format: <irq>,<irq>... 	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] empty param disables _OSI 	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_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_dbg_layer=	[HW,ACPI]			Format: <int>			Each bit of the <int> indicates an ACPI debug layer,			1: enable, 0: disable. It is useful for boot time			debugging. After system has booted up, it can be set			via /proc/acpi/debug_layer. 	acpi_dbg_level=	[HW,ACPI]			Format: <int>			Each bit of the <int> indicates an ACPI debug level,			1: enable, 0: disable. It is useful for boot time			debugging. After system has booted up, it can be set			via /proc/acpi/debug_level. 	acpi_fake_ecdt	[HW,ACPI] Workaround failure due to BIOS lacking ECDT 	acpi_generic_hotkey [HW,ACPI]			Allow consolidated generic hotkey driver to			override platform specific driver.			See also Documentation/acpi-hotkey.txt. 	acpi_pm_good	[IA-32,X86-64]			Override the pmtimer bug detection: force the kernel			to assume that this machine's pmtimer latches its value			and always returns good values. 	enable_timer_pin_1 [i386,x86-64]			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. 	disable_timer_pin_1 [i386,x86-64]			Disable PIN 1 of APIC timer			Can be useful to work around chipset bugs. 	ad1816=		[HW,OSS]			Format: <io>,<irq>,<dma>,<dma2>			See also Documentation/sound/oss/AD1816. 	ad1848=		[HW,OSS]			Format: <io>,<irq>,<dma>,<dma2>,<type> 	adlib=		[HW,OSS]			Format: <io> 	advansys=	[HW,SCSI]			See header of drivers/scsi/advansys.c. 	advwdt=		[HW,WDT] Advantech WDT			Format: <iostart>,<iostop> 	aedsp16=	[HW,OSS] Audio Excel DSP 16			Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>			See also header of sound/oss/aedsp16.c. 	aha152x=	[HW,SCSI]			See Documentation/scsi/aha152x.txt. 	aha1542=	[HW,SCSI]			Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]] 	aic7xxx=	[HW,SCSI]			See Documentation/scsi/aic7xxx.txt. 	aic79xx=	[HW,SCSI]			See Documentation/scsi/aic79xx.txt. 	amijoy.map=	[HW,JOY] Amiga joystick support			Map of devices attached to JOY0DAT and JOY1DAT			Format: <a>,<b>			See also Documentation/kernel/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,i386] 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. 	apm=		[APM] Advanced Power Management			See header of arch/i386/kernel/apm.c. 	applicom=	[HW]			Format: <mem>,<irq> 	arcrimi=	[HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards			Format: <io>,<irq>,<nodeID> 	ataflop=	[HW,M68k] 	atarimouse=	[HW,MOUSE] Atari Mouse 	atascsi=	[HW,SCSI] Atari SCSI 	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 	autotest	[IA64] 	aztcd=		[HW,CD] Aztech CD268 CDROM driver			Format: <io>,0x79 (?) 	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. 	blkmtd_device=	[HW,MTD]	blkmtd_erasesz=	blkmtd_ro=	blkmtd_bs=	blkmtd_count= 	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=	and Documentation/video4linux/bttv/CARDLIST 	BusLogic=	[HW,SCSI]			See drivers/scsi/BusLogic.c, comment before function			BusLogic_ParseDriverOptions(). 	c101=		[NET] Moxa C101 synchronous serial card 	cachesize=	[BUGS=IA-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. 	cdu31a=		[HW,CD]			Format: <io>,<irq>[,PAS]			See header of drivers/cdrom/cdu31a.c. 	chandev=	[HW,NET] Generic channel device initialisation 	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. 	clock=		[BUGS=IA-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 } 	code_bytes	[IA32] How many bytes of object code to print in an			oops report.			Range: 0 - 8192			Default: 64 	disable_8254_timer	enable_8254_timer			[IA32/X86_64] Disable/Enable interrupt 0 timer routing			over the 8254 in addition to over the IO-APIC. The			kernel tries to set a sensible default. 	hpet=		[IA-32,HPET] option to disable HPET and use PIT.			Format: disable 	cm206=		[HW,CD]			Format: { auto | [<io>,][<irq>] } 	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= 	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/serial-console.txt for more			information.  See			Documentation/networking/netconsole.txt for an			alternative. 		uart,io,<addr>[,options]		uart,mmio,<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.  The			options are the same as for ttyS, above. 	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver			Format:			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 	cpia_pp=	[HW,PPT]			Format: { parport<nr> | auto | none } 	crashkernel=nn[KMG]@ss[KMG]			[KNL] Reserve a chunk of physical memory to			hold a kernel to switch to with kexec on panic. 	cs4232=		[HW,OSS]			Format: <io>,<irq>,<dma>,<dma2>,<mpuio>,<mpuirq> 	cs89x0_dma=	[HW,NET]			Format: <dma> 	cs89x0_media=	[HW,NET]			Format: { rj45 | aui | bnc } 	cyclades=	[HW,SERIAL] Cyclades multi-serial port adapter. 	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: <port#>,<type>			See also Documentation/input/joystick-parport.txt 	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. 	decnet=		[HW,NET]			Format: <area>[,<node>]			See also Documentation/networking/decnet.txt. 	dhash_entries=	[KNL]			Set number of hash buckets for dentry cache. 	digi=		[HW,SERIAL]			IO parameters + enable/disable command. 	digiepca=	[HW,SERIAL]			See drivers/char/README.epca and			Documentation/digiepca.txt. 	dmascc=		[HW,AX25,SERIAL] AX.25 Z80SCC driver with DMA			support available.			Format: <io_dev0>[,<io_dev1>[,..<io_dev32>]] 	dmasound=	[HW,OSS] Sound subsystem buffers 	dscc4.setup=	[NET] 	dtc3181e=	[HW,SCSI] 	earlyprintk=	[IA-32,X86-64,SH]			earlyprintk=vga			earlyprintk=serial[,ttySn[,baudrate]] 			Append ",keep" to not disable it when the real console

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