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                          Kernel Parameters
                          ~~~~~~~~~~~~~~~~~
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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.
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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

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Double-quotes can be used to protect spaces in values, e.g.:
	param="spaces in here"
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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}".

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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:
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	ACPI	ACPI support is enabled.
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	AGP	AGP (Accelerated Graphics Port) is enabled.
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	ALSA	ALSA sound support is enabled.
	APIC	APIC support is enabled.
	APM	Advanced Power Management support is enabled.
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	ARM	ARM architecture is enabled.
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	AVR32	AVR32 architecture is enabled.
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	AX25	Appropriate AX.25 support is enabled.
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	BLACKFIN Blackfin architecture is enabled.
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	CLK	Common clock infrastructure is enabled.
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	CMA	Contiguous Memory Area support is enabled.
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	DRM	Direct Rendering Management support is enabled.
	DYNAMIC_DEBUG Build in debug messages and enable them at runtime
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	EDD	BIOS Enhanced Disk Drive Services (EDD) is enabled
	EFI	EFI Partitioning (GPT) is enabled
	EIDE	EIDE/ATAPI support is enabled.
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	EVM	Extended Verification Module
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	FB	The frame buffer device is enabled.
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	FTRACE	Function tracing enabled.
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	GCOV	GCOV profiling is enabled.
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	HW	Appropriate hardware is enabled.
	IA-64	IA-64 architecture is enabled.
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	IMA     Integrity measurement architecture is enabled.
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	IOSCHED	More than one I/O scheduler is enabled.
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	IP_PNP	IP DHCP, BOOTP, or RARP is enabled.
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	IPV6	IPv6 support is enabled.
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	ISAPNP	ISA PnP code is enabled.
	ISDN	Appropriate ISDN support is enabled.
	JOY	Appropriate joystick support is enabled.
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	KGDB	Kernel debugger support is enabled.
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	KVM	Kernel Virtual Machine support is enabled.
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	LIBATA  Libata driver is enabled
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	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.
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	MIPS	MIPS architecture is enabled.
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	MOUSE	Appropriate mouse support is enabled.
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	MSI	Message Signaled Interrupts (PCI).
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	MTD	MTD (Memory Technology Device) support is enabled.
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	NET	Appropriate network support is enabled.
	NUMA	NUMA support is enabled.
	NFS	Appropriate NFS support is enabled.
	OSS	OSS sound support is enabled.
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	PV_OPS	A paravirtualized kernel is enabled.
	PARIDE	The ParIDE (parallel port IDE) subsystem is enabled.
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	PARISC	The PA-RISC architecture is enabled.
	PCI	PCI bus support is enabled.
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	PCIE	PCI Express support is enabled.
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	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.
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			A lot of drivers have their options described inside
			the Documentation/scsi/ sub-directory.
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	SECURITY Different security models are enabled.
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	SELINUX SELinux support is enabled.
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	APPARMOR AppArmor support is enabled.
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	SERIAL	Serial support is enabled.
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	SH	SuperH architecture is enabled.
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	SMP	The kernel is an SMP kernel.
	SPARC	Sparc architecture is enabled.
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	SWSUSP	Software suspend (hibernation) is enabled.
	SUSPEND	System suspend states are enabled.
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	TPM	TPM drivers are enabled.
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	TS	Appropriate touchscreen support is enabled.
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	UMS	USB Mass Storage support is enabled.
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	USB	USB support is enabled.
	USBHID	USB Human Interface Device support is enabled.
	V4L	Video For Linux support is enabled.
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	VMMIO   Driver for memory mapped virtio devices is enabled.
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	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.
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	X86-32	X86-32, aka i386 architecture is enabled.
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	X86-64	X86-64 architecture is enabled.
			More X86-64 boot options can be found in
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			Documentation/x86/x86_64/boot-options.txt .
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	X86	Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
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	XEN	Xen support is enabled
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In addition, the following text indicates that the option:

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

Parameters denoted with BOOT are actually interpreted by the boot
loader, and have no meaning to the kernel directly.
Do not modify the syntax of boot loader parameters without extreme
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need or coordination with <Documentation/x86/boot.txt>.
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There are also arch-specific kernel-parameters not documented here.
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See for example <Documentation/x86/x86_64/boot-options.txt>.
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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.

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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.

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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.

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	acpi=		[HW,ACPI,X86]
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			Advanced Configuration and Power Interface
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			Format: { force | off | strict | noirq | rsdt }
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			force -- enable ACPI if default was off
			off -- disable ACPI if default was on
			noirq -- do not use ACPI for IRQ routing
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			strict -- Be less tolerant of platforms that are not
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				strictly ACPI specification compliant.
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			rsdt -- prefer RSDT over (default) XSDT
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			copy_dsdt -- copy DSDT to memory
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			See also Documentation/power/runtime_pm.txt, pci=noacpi
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	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.

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	acpi_apic_instance=	[ACPI, IOAPIC]
			Format: <int>
			2: use 2nd APIC table, if available
			1,0: use 1st APIC table
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			default: 0
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	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.

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	acpi.debug_layer=	[HW,ACPI,ACPI_DEBUG]
	acpi.debug_level=	[HW,ACPI,ACPI_DEBUG]
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			Format: <int>
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			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, ...
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			The debug_level mask defaults to "info".  See
			Documentation/acpi/debug.txt for more information about
			debug layers and levels.
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			Enable processor driver info messages:
			    acpi.debug_layer=0x20000000
			Enable PCI/PCI interrupt routing info messages:
			    acpi.debug_layer=0x400000
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			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.
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	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.

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	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>...

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	acpi_no_auto_serialize	[HW,ACPI]
			Disable auto-serialization of AML methods
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			AML control methods that contain the opcodes to create
			named objects will be marked as "Serialized" by the
			auto-serialization feature.
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			This feature is enabled by default.
			This option allows to turn off the feature.
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	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.
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	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.

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	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
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			acpi_osi="string1"	# add string1
			acpi_osi="!string2"	# remove string2
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			acpi_osi=!*		# remove all strings
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			acpi_osi=!		# disable all built-in OS vendor
						  strings
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			acpi_osi=		# disable all strings

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			'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
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			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.
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			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.

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			'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.

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	acpi_pm_good	[X86]
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			Override the pmtimer bug detection: force the kernel
			to assume that this machine's pmtimer latches its value
			and always returns good values.

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	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,
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				  old_ordering, nonvs, sci_force_enable }
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			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).
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			nonvs prevents the kernel from saving/restoring the
			ACPI NVS memory during suspend/hibernation and resume.
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			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).
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	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

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	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.

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	acpi_no_memhotplug [ACPI] Disable memory hotplug.  Useful for kdump
			   kernels.

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	add_efi_memmap	[EFI; X86] Include EFI memory map in
			kernel's map of available physical RAM.

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	agp=		[AGP]
			{ off | try_unsupported }
			off: disable AGP support
			try_unsupported: try to drive unsupported chipsets
				(may crash computer or cause data corruption)

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	ALSA		[HW,ALSA]
			See Documentation/sound/alsa/alsa-parameters.txt

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	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.

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	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.

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			32: only for 32-bit processes
			64: only for 64-bit processes
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			on: enable for both 32- and 64-bit processes
			off: disable for both 32- and 64-bit processes

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	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.

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	amd_iommu=	[HW,X86-64]
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			Pass parameters to the AMD IOMMU driver in the system.
			Possible values are:
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			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
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			off	  - do not initialize any AMD IOMMU found in
				    the system
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			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
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	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.

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	amijoy.map=	[HW,JOY] Amiga joystick support
			Map of devices attached to JOY0DAT and JOY1DAT
			Format: <a>,<b>
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			See also Documentation/input/joystick.txt
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	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>

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	apc=		[HW,SPARC]
			Power management functions (SPARCstation-4/5 + deriv.)
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			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.

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	apic=		[APIC,X86-32] Advanced Programmable Interrupt Controller
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			Change the output verbosity whilst booting
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			Format: { quiet (default) | verbose | debug }
			Change the amount of debugging information output
			when initialising the APIC and IO-APIC components.
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	autoconf=	[IPV6]
			See Documentation/networking/ipv6.txt.

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	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

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	apm=		[APM] Advanced Power Management
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			See header of arch/x86/kernel/apm_32.c.
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	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

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	atkbd.set=	[HW] Select keyboard code set
			Format: <int> (2 = AT (default), 3 = PS/2)
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	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))
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	atkbd.softrepeat= [HW]
			Use software keyboard repeat
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	audit=		[KNL] Enable the audit sub-system
			Format: { "0" | "1" } (0 = disabled, 1 = enabled)
508 509 510 511 512 513 514 515
			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.
516
			Default: unset
517

518 519 520 521
	audit_backlog_limit= [KNL] Set the audit queue size limit.
			Format: <int> (must be >=0)
			Default: 64

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	baycom_epp=	[HW,AX25]
			Format: <io>,<mode>
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	baycom_par=	[HW,AX25] BayCom Parallel Port AX.25 Modem
			Format: <io>,<mode>
			See header of drivers/net/hamradio/baycom_par.c.

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	baycom_ser_fdx=	[HW,AX25]
			BayCom Serial Port AX.25 Modem (Full Duplex Mode)
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			Format: <io>,<irq>,<mode>[,<baud>]
			See header of drivers/net/hamradio/baycom_ser_fdx.c.

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	baycom_ser_hdx=	[HW,AX25]
			BayCom Serial Port AX.25 Modem (Half Duplex Mode)
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			Format: <io>,<irq>,<mode>
			See header of drivers/net/hamradio/baycom_ser_hdx.c.

539 540 541 542
	blkdevparts=	Manual partition parsing of block device(s) for
			embedded devices based on command line input.
			See Documentation/block/cmdline-partition.txt

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	boot_delay=	Milliseconds to delay each printk during boot.
			Values larger than 10 seconds (10000) are changed to
			no delay (0).
			Format: integer

548 549
	bootmem_debug	[KNL] Enable bootmem allocator debug messages.

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	bttv.card=	[HW,V4L] bttv (bt848 + bt878 based grabber cards)
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	bttv.radio=	Most important insmod options are available as
			kernel args too.
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	bttv.pll=	See Documentation/video4linux/bttv/Insmod-options
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	bttv.tuner=
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556 557 558 559
	bulk_remove=off	[PPC]  This parameter disables the use of the pSeries
			firmware feature for flushing multiple hpte entries
			at a time.

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	c101=		[NET] Moxa C101 synchronous serial card

562
	cachesize=	[BUGS=X86-32] Override level 2 CPU cache size detection.
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			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.

569 570 571
	ca_keys=	[KEYS] This parameter identifies a specific key(s) on
			the system trusted keyring to be used for certificate
			trust validation.
572
			format: { id:<keyid> | builtin }
573

574 575 576 577 578 579
	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).

580 581
	ccw_timeout_log [S390]
			See Documentation/s390/CommonIO for details.
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583 584
	cgroup_disable= [KNL] Disable a particular controller
			Format: {name of the controller(s) to disable}
585 586 587 588 589 590 591 592
			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}
593

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	checkreqprot	[SELINUX] Set initial checkreqprot flag value.
			Format: { "0" | "1" }
			See security/selinux/Kconfig help text.
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			0 -- check protection applied by kernel (includes
				any implied execute protection).
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			1 -- check protection requested by application.
			Default value is set via a kernel config option.
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			Value can be changed at runtime via
				/selinux/checkreqprot.

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	cio_ignore=	[S390]
			See Documentation/s390/CommonIO for details.
606 607
	clk_ignore_unused
			[CLK]
608 609 610 611 612 613 614 615 616
			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.
617

618
	clock=		[BUGS=X86-32, HW] gettimeofday clocksource override.
619
			[Deprecated]
620
			Forces specified clocksource (if available) to be used
621
			when calculating gettimeofday(). If specified
622
			clocksource is not available, it defaults to PIT.
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			Format: { pit | tsc | cyclone | pmtmr }

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	clocksource=	Override the default clocksource
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			Format: <string>
			Override the default clocksource and use the clocksource
			with the name specified.
			Some clocksource names to choose from, depending on
			the platform:
			[all] jiffies (this is the base, fallback clocksource)
			[ACPI] acpi_pm
			[ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
				pxa_timer,timer3,32k_counter,timer0_1
			[AVR32] avr32
636
			[X86-32] pit,hpet,tsc;
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				scx200_hrt on Geode; cyclone on IBM x440
			[MIPS] MIPS
			[PARISC] cr16
			[S390] tod
			[SH] SuperH
			[SPARC64] tick
			[X86-64] hpet,tsc

645 646
	clearcpuid=BITNUM [X86]
			Disable CPUID feature X for the kernel. See
647 648
			arch/x86/include/asm/cpufeature.h for the valid bit
			numbers. Note the Linux specific bits are not necessarily
649 650 651 652 653 654 655 656 657
			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.

658 659 660 661 662
	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
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			memory allocations. A value of 0 disables CMA
			altogether. For more information, see
665 666
			include/linux/dma-contiguous.h

667 668 669 670 671 672 673
	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

674 675
	coherent_pool=nn[KMG]	[ARM,KNL]
			Sets the size of memory pool for coherent, atomic dma
676
			allocations, by default set to 256K.
677

678
	code_bytes	[X86] How many bytes of object code to print
679
			in an oops report.
680 681 682
			Range: 0 - 8192
			Default: 64

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	com20020=	[HW,NET] ARCnet - COM20020 chipset
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			Format:
			<io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
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	com90io=	[HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
			Format: <io>[,<irq>]

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	com90xx=	[HW,NET]
			ARCnet - COM90xx chipset (memory-mapped buffers)
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			Format: <io>[,<irq>[,<memstart>]]

	condev=		[HW,S390] console device
	conmode=
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	console=	[KNL] Output console device and options.

		tty<n>	Use the virtual console device <n>.

		ttyS<n>[,options]
702
		ttyUSB0[,options]
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			Use the specified serial port.  The options are of
704 705 706 707 708 709 710 711 712
			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.
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714 715
		uart[8250],io,<addr>[,options]
		uart[8250],mmio,<addr>[,options]
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			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.
720 721
		hvc<n>	Use the hypervisor console device <n>. This is for
			both Xen and PowerPC hypervisors.
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723 724 725 726 727
                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.

728 729 730 731
	consoleblank=	[KNL] The console blank (screen saver) timeout in
			seconds. Defaults to 10*60 = 10mins. A value of 0
			disables the blank timer.

732 733 734 735 736
	coredump_filter=
			[KNL] Change the default value for
			/proc/<pid>/coredump_filter.
			See also Documentation/filesystems/proc.txt.

737 738 739
	cpuidle.off=1	[CPU_IDLE]
			disable the cpuidle sub-system

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	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver
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			Format:
			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
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744 745 746 747 748 749 750
	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.
751

752 753 754 755 756
	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
757
			Documentation/kdump/kdump.txt for an example.
758

759
	crashkernel=size[KMG],high
760 761 762 763 764 765
			[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.
766 767 768
	crashkernel=size[KMG],low
			[KNL, x86_64] range under 4G. When crashkernel=X,high
			is passed, kernel could allocate physical memory region
769 770 771 772 773 774 775
			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.
776
			It will be ignored when crashkernel=X,high is not used
777
			or memory reserved is below 4G.
778

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	cs89x0_dma=	[HW,NET]
			Format: <dma>

	cs89x0_media=	[HW,NET]
			Format: { rj45 | aui | bnc }
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	dasd=		[HW,NET]
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			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

793 794
	ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
			time. See Documentation/dynamic-debug-howto.txt for
795
			details.  Deprecated, see dyndbg.
796

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	debug		[KNL] Enable kernel debugging (events log level).

799 800 801 802 803 804 805 806 807
	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.

808 809
	debug_objects	[KNL] Enable object debugging

810 811 812
	no_debug_objects
			[KNL] Disable object debugging

813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831
	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.

832 833
	debugpat	[X86] Enable PAT debugging

834
	decnet.addr=	[HW,NET]
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			Format: <area>[,<node>]
			See also Documentation/networking/decnet.txt.

838 839 840 841 842 843 844
	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.
845

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	dhash_entries=	[KNL]
			Set number of hash buckets for dentry cache.
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	disable=	[IPV6]
			See Documentation/networking/ipv6.txt.

852 853 854 855 856 857 858 859 860
	disable_cpu_apicid= [X86,APIC,SMP]
			Format: <int>
			The number of initial APIC ID for the
			corresponding CPU to be disabled at boot,
			mostly used for the kdump 2nd kernel to
			disable BSP to wake up multiple CPUs without
			causing system reset or hang due to sending
			INIT from AP to BSP.

861 862 863 864
	disable_ddw     [PPC/PSERIES]
			Disable Dynamic DMA Window support. Use this if
			to workaround buggy firmware.

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	disable_ipv6=	[IPV6]
			See Documentation/networking/ipv6.txt.

868 869 870
	disable_mtrr_cleanup [X86]
			The kernel tries to adjust MTRR layout from continuous
			to discrete, to make X server driver able to add WB
871
			entry later. This parameter disables that.
872

873
	disable_mtrr_trim [X86, Intel and AMD only]
874 875 876 877 878
			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.

879
	disable_timer_pin_1 [X86]
880 881 882 883 884 885 886 887 888 889 890 891 892
			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=<number>
			This option allows to tune the number of preallocated
			entries for DMA-API debugging code. One entry is
			required per DMA-API allocation. Use this if the
			DMA-API debugging code disables itself because the
			architectural default is too low.

893 894 895 896 897 898 899
	dma_debug_driver=<driver_name>
			With this option the DMA-API debugging driver
			filter feature can be enabled at boot time. Just
			pass the driver to filter for as the parameter.
			The filter can be disabled or changed to another
			driver later using sysfs.

900 901 902 903 904 905 906 907 908 909 910 911 912 913 914
	drm_kms_helper.edid_firmware=[<connector>:]<file>
			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.

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	dscc4.setup=	[NET]

917 918 919 920 921
	dyndbg[="val"]		[KNL,DYNAMIC_DEBUG]
	module.dyndbg[="val"]
			Enable debug messages at boot time.  See
			Documentation/dynamic-debug-howto.txt for details.

922 923 924 925 926
	early_ioremap_debug [KNL]
			Enable debug messages in early_ioremap support. This
			is useful for tracking down temporary early mappings
			which are not unmapped.

927
	earlycon=	[KNL] Output early console device and options.
928

929 930 931 932 933 934
		cdns,<addr>
			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.

935 936
		uart[8250],io,<addr>[,options]
		uart[8250],mmio,<addr>[,options]
937
		uart[8250],mmio32,<addr>[,options]
938 939
			Start an early, polled-mode console on the 8250/16550
			UART at the specified I/O port or MMIO address.
940 941
			MMIO inter-register address stride is either 8-bit
			(mmio) or 32-bit (mmio32).
942 943
			The options are the same as for ttyS, above.

944 945 946 947 948 949
		pl011,<addr>
			Start an early, polled-mode console on a pl011 serial
			port at the specified address. The pl011 serial port
			must already be setup and configured. Options are not
			yet supported.

950 951 952 953 954 955 956 957 958 959 960 961
		msm_serial,<addr>
			Start an early, polled-mode console on an msm serial
			port at the specified address. The serial port
			must already be setup and configured. Options are not
			yet supported.

		msm_serial_dm,<addr>
			Start an early, polled-mode console on an msm serial
			dm port at the specified address. The serial port
			must already be setup and configured. Options are not
			yet supported.

962 963
		smh	Use ARM semihosting calls for early console.

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	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k]
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			earlyprintk=vga
966
			earlyprintk=efi
967
			earlyprintk=xen
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			earlyprintk=serial[,ttySn[,baudrate]]
969
			earlyprintk=serial[,0x...[,baudrate]]
970
			earlyprintk=ttySn[,baudrate]
971
			earlyprintk=dbgp[debugController#]
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973 974 975 976
			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.

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			Append ",keep" to not disable it when the real console
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			takes over.

980 981
			Only one of vga, efi, serial, or usb debug port can
			be used at a time.
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983 984 985 986 987 988 989 990
			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 ...
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			Interaction with the standard serial driver is not
			very good.

995 996
			The VGA and EFI output is eventually overwritten by
			the real console.
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998 999
			The xen output can only be used by Xen PV guests.

1000 1001 1002 1003 1004 1005 1006 1007
	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.

1008 1009 1010
	ekgdboc=	[X86,KGDB] Allow early kernel console debugging
			ekgdboc=kbd

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			This is designed to be used in conjunction with
1012 1013
			the boot argument: earlyprintk=vga

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	edd=		[EDD]
1015
			Format: {"off" | "on" | "skip[mbr]"}
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1017 1018 1019 1020 1021 1022
	efi=		[EFI]
			Format: { "old_map" }
			old_map [X86-64]: switch to the old ioremap-based EFI
			runtime services mapping. 32-bit still uses this one by
			default.

1023 1024 1025 1026 1027 1028
	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.

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	eisa_irq_edge=	[PARISC,HW]
			See header of drivers/parisc/eisa.c.

1032
	elanfreq=	[X86-32]
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			See comment before function elanfreq_setup() in
1034
			arch/x86/kernel/cpu/cpufreq/elanfreq.c.
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	elevator=	[IOSCHED]
1037
			Format: {"cfq" | "deadline" | "noop"}
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			See Documentation/block/cfq-iosched.txt and
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			Documentation/block/deadline-iosched.txt for details.

1041
	elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
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			Specifies physical address of start of kernel core
1043 1044
			image elf header and optionally the size. Generally
			kexec loader will pass this option to capture kernel.
1045
			See Documentation/kdump/kdump.txt for details.
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1047 1048 1049 1050 1051
	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.

1052
	enable_timer_pin_1 [X86]
1053 1054 1055 1056 1057
			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.

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	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.

1066 1067 1068 1069
	erst_disable	[ACPI]
			Disable Error Record Serialization Table (ERST)
			support.

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	ether=		[HW,NET] Ethernet cards parameters
			This option is obsoleted by the "netdev=" option, which
			has equivalent usage. See its documentation for details.

1074 1075 1076 1077 1078
	evm=		[EVM]
			Format: { "fix" }
			Permit 'security.evm' to be updated regardless of
			current integrity status.

1079 1080 1081 1082 1083
	failslab=
	fail_page_alloc=
	fail_make_request=[KNL]
			General fault injection mechanism.
			Format: <interval>,<probability>,<space>,<times>
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			See also Documentation/fault-injection/.
1085

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	floppy=		[HW]
1087
			See Documentation/blockdev/floppy.txt.
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1089 1090 1091 1092 1093 1094
	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.

1095 1096 1097 1098 1099 1100 1101
	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.

1102
	ftrace=[tracer]
1103
			[FTRACE] will set and start the specified tracer
1104 1105 1106
			as early as possible in order to facilitate early
			boot debugging.

1107
	ftrace_dump_on_oops[=orig_cpu]
1108
			[FTRACE] will dump the trace buffers on oops.
1109 1110 1111 1112
			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.
1113 1114 1115 1116 1117 1118

	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
1119
			tracing directory.
1120 1121 1122 1123 1124 1125

	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.
1126

1127 1128 1129 1130 1131 1132 1133
	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.

1134 1135 1136 1137 1138 1139
	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.

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	gamecon.map[2|3]=
			[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
			support via parallel port (up to 5 devices per port)
			Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
			See also Documentation/input/joystick-parport.txt

	gamma=		[HW,DRM]

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	gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
			Format: off | on
			default: on

1152 1153 1154 1155 1156 1157
	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.

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	gpt		[EFI] Forces disk with valid GPT signature but
1159 1160 1161
			invalid Protective MBR to be treated as GPT. If the
			primary GPT is corrupted, it enables the backup/alternate
			GPT to be used instead.
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1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180
	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: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
			Default: 1024
	grcan.rxsize=	[HW] Sets the size of the rx buffer.
			Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
			Default: 1024

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	hashdist=	[KNL,NUMA] Large hashes allocated during boot
			are distributed across NUMA nodes.  Defaults on
1183
			for 64-bit NUMA, off otherwise.
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			Format: 0 | 1 (for off | on)
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	hcl=		[IA-64] SGI's Hardware Graph compatibility layer

	hd=		[EIDE] (E)IDE hard drive subsystem geometry
			Format: <cyl>,<head>,<sect>

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	hest_disable	[ACPI]
			Disable Hardware Error Source Table (HEST) support;
			corresponding firmware-first mode error processing
			logic will be disabled.

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	highmem=nn[KMG]	[KNL,BOOT] forces the highmem zone to have an exact
			size of <nn>. This works even on boxes that have no
			highmem otherwise. This also works to reduce highmem
			size on bigger boxes.

1201 1202 1203 1204
	highres=	[KNL] Enable/disable high resolution timer mode.
			Valid parameters: "on", "off"
			Default: "on"

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	hisax=		[HW,ISDN]
			See Documentation/isdn/README.HiSax.

1208 1209 1210 1211 1212 1213 1214 1215 1216 1217
	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

1218 1219 1220
	hpet_mmap=	[X86, HPET_MMAP] Allow userspace to mmap HPET
			registers.  Default set by CONFIG_HPET_MMAP_DEFAULT.

1221 1222
	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.
1223 1224 1225 1226 1227
			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)
1228 1229
			Note that 1GB pages can only be allocated at boot time
			using hugepages= and not freed afterwards.
1230

1231 1232
	hvc_iucv=	[S390] Number of z/VM IUCV hypervisor console (HVC)
			       terminal devices. Valid values: 0..8
1233 1234 1235
	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.
1236

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	hwthread_map=	[METAG] Comma-separated list of Linux cpu id to
			        hardware thread id mappings.
				Format: <cpu>:<hwthread>

1241 1242 1243 1244 1245 1246
	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.

1247
	i2c_bus=	[HW] Override the default board specific I2C bus speed
1248 1249
			     or register an additional I2C bus that is not
			     registered from board initialization code.
1250 1251 1252
			     Format:
			     <bus_id>,<clkrate>

1253
	i8042.debug	[HW] Toggle i8042 debug mode
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	i8042.direct	[HW] Put keyboard port into non-translated mode
1255 1256
	i8042.dumbkbd	[HW] Pretend that controller can only read data from
			     keyboard and cannot control its state
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			     (Don't attempt to blink the leds)
	i8042.noaux	[HW] Don't check for auxiliary (== mouse) port
1259
	i8042.nokbd	[HW] Don't check/create keyboard port
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	i8042.noloop	[HW] Disable the AUX Loopback command while probing
			     for the AUX port
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	i8042.nomux	[HW] Don't check presence of an active multiplexing
1263
			     controller. Default: true.
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	i8042.nopnp	[HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
			     controllers
1266
	i8042.notimeout	[HW] Ignore timeout condition signalled by controller
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	i8042.reset	[HW] Reset the controller during init and cleanup
	i8042.unlock	[HW] Unlock (ignore) the keylock

	i810=		[HW,DRM]

1272 1273 1274
	i8k.ignore_dmi	[HW] Continue probing hardware even if DMI data
			indicates that the driver is running on unsupported
			hardware.
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	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.

1283
	i915.invert_brightness=
1284 1285
			[DRM] Invert the sense of the variable that is used to
			set the brightness of the panel backlight. Normally a
1286 1287 1288 1289 1290 1291 1292 1293 1294 1295
			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
1296

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	icn=		[HW,ISDN]
			Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]

1300 1301
	ide-core.nodma=	[HW] (E)IDE subsystem
			Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1302 1303
			.vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
			.cdrom .chs .ignore_cable are additional options
1304
			See Documentation/ide/ide.txt.
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1306 1307 1308
	ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
			Claim all unknown PCI IDE storage controllers.

1309
	idle=		[X86]
1310
			Format: idle=poll, idle=halt, idle=nomwait
1311 1312 1313 1314 1315
			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.
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			In such case C2/C3 won't be used again.
1317
			idle=nomwait: Disable mwait for CPU C-states
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1319 1320 1321
	ignore_loglevel	[KNL]
			Ignore loglevel setting - this will print /all/
			kernel messages to the console. Useful for debugging.
1322 1323 1324
			We also add it as printk module parameter, so users
			could change it dynamically, usually by
			/sys/module/printk/parameters/ignore_loglevel.
1325

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	ihash_entries=	[KNL]
			Set number of hash buckets for inode cache.

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	ima_appraise=	[IMA] appraise integrity measurements
1330
			Format: { "off" | "enforce" | "fix" | "log" }
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			default: "enforce"

1333 1334 1335 1336
	ima_appraise_tcb [IMA]
			The builtin appraise policy appraises all files
			owned by uid=0.

1337
	ima_hash=	[IMA]
1338 1339
			Format: { md5 | sha1 | rmd160 | sha256 | sha384
				   | sha512 | ... }
1340 1341
			default: "sha1"

1342 1343 1344
			The list of supported hash algorithms is defined
			in crypto/hash_info.h.

1345 1346 1347 1348 1349 1350
	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.

1351 1352 1353 1354 1355
	ima_template=   [IMA]
			Select one of defined IMA measurements template formats.
			Formats: { "ima" | "ima-ng" }
			Default: "ima-ng"

1356 1357 1358 1359 1360 1361 1362 1363 1364
	ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
			Format: <min_file_size>
			Set the minimal file size for using asynchronous hash.
			If left unspecified, ahash usage is disabled.

			ahash performance varies for different data sizes on
			different crypto accelerators. This option can be used
			to achieve the best performance for a particular HW.

1365 1366 1367 1368 1369 1370 1371 1372
	ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
			Format: <bufsize>
			Set hashing buffer size. Default: 4k.

			ahash performance varies for different chunk sizes on
			different crypto accelerators. This option can be used
			to achieve best performance for particular HW.

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	init=		[KNL]
			Format: <full_path>
			Run specified binary instead of /sbin/init as init
			process.

	initcall_debug	[KNL] Trace initcalls as they are executed.  Useful
			for working out where the kernel is dying during
			startup.

1382 1383 1384 1385
	initcall_blacklist=  [KNL] Do not execute a comma-separated list of
			initcall functions.  Useful for debugging built-in
			modules and initcalls.

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	initrd=		[BOOT] Specify the location of the initial ramdisk

	inport.irq=	[HW] Inport (ATI XL and Microsoft) busmouse driver
			Format: <irq>

1391 1392
	int_pln_enable  [x86] Enable power limit notification interrupt

1393 1394 1395 1396 1397
	integrity_audit=[IMA]
			Format: { "0" | "1" }
			0 -- basic integrity auditing messages. (Default)
			1 -- additional integrity auditing messages.

1398
	intel_iommu=	[DMAR] Intel IOMMU driver (DMAR) option
1399 1400
		on
			Enable intel iommu driver.
1401 1402 1403 1404 1405 1406 1407 1408
		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.
1409 1410
		forcedac [x86_64]
			With this option iommu will not optimize to look
1411
			for io virtual address below 32-bit forcing dual
1412
			address cycle on pci bus for cards supporting greater
1413 1414
			than 32-bit addressing. The default is to look
			for translation below 32-bit and if not available
1415
			then look in the higher range.
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		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.
1420 1421 1422 1423
		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.
1424 1425 1426 1427 1428

	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.

1429 1430 1431 1432 1433
	intel_pstate=  [X86]
		       disable
		         Do not enable intel_pstate as the default
		         scaling driver for the supported processors

1434 1435 1436 1437
	intremap=	[X86-64, Intel-IOMMU]
			on	enable Interrupt Remapping (default)
			off	disable Interrupt Remapping
			nosid	disable Source ID checking
1438 1439
			no_x2apic_optout
				BIOS x2APIC opt-out request will be ignored
1440

1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455
	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
1456 1457
		pt		[x86, IA-64]

1458 1459 1460 1461 1462

	io7=		[HW] IO7 for Marvel based alpha systems
			See comment before marvel_specify_io7 in
			arch/alpha/kernel/core_marvel.c.

1463
	io_delay=	[X86] I/O delay method
1464 1465 1466 1467
		0x80
			Standard port 0x80 based delay
		0xed
			Alternate port 0xed based delay (needed on some systems)
1468
		udelay
1469 1470 1471
			Simple two microseconds delay
		none
			No delay
1472

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	ip=		[IP_PNP]
1474
			See Documentation/filesystems/nfs/nfsroot.txt.
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	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.

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	isapnp=		[ISAPNP]
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			Format: <RDP>,<reset>,<pci_scan>,<verbosity>
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	isolcpus=	[KNL,SMP] Isolate CPUs from the general scheduler.
1491 1492 1493
			Format:
			<cpu number>,...,<cpu number>
			or
1494 1495
			<cpu number>-<cpu number>
			(must be a positive range in ascending order)
1496 1497
			or a mixture
			<cpu number>,...,<cpu number>-<cpu number>
1498

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			This option can be used to specify one or more CPUs
			to isolate from the general SMP balancing and scheduling
1501 1502
			algorithms. You can move a process onto or off an
			"isolated" CPU via the CPU affinity syscalls or cpuset.
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			<cpu number> begins at 0 and the maximum value is
			"number of CPUs in system - 1".

			This option is the preferred way to isolate CPUs. The
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			alternative -- manually setting the CPU mask of all
			tasks in the system -- can cause problems and
			suboptimal load balancer performance.
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	iucv=		[HW,NET]
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1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526
	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

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	js=		[HW,JOY] Analog joystick
			See Documentation/input/joystick.txt.

1530 1531 1532 1533 1534 1535 1536
	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.

1537 1538
	keepinitrd	[HW,ARM]

1539
	kernelcore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
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			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
1547
			of Movable pages.  The Movable zone is used for the
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			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.

1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565
	kgdbdbgp=	[KGDB,HW] kgdb over EHCI usb debug port.
			Format: <Controller#>[,poll interval]
			The controller # is the number of the ehci usb debug
			port as it is probed via PCI.  The poll interval is
			optional and is the number seconds in between
			each poll cycle to the debug port in case you need
			the functionality for interrupting the kernel with
			gdb or control-c on the dbgp connection.  When
			not using this parameter you use sysrq-g to break into
			the kernel debugger.

1566
	kgdboc=		[KGDB,HW] kgdb over consoles.
1567 1568
			Requires a tty driver that supports console polling,
			or a supported polling keyboard driver (non-usb).
1569 1570 1571 1572 1573 1574
			 Serial only format: <serial_device>[,baud]
			 keyboard only format: kbd
			 keyboard and serial format: kbd,<serial_device>[,baud]
			Optional Kernel mode setting:
			 kms, kbd format: kms,kbd
			 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
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1576 1577 1578
	kgdbwait	[KGDB] Stop kernel execution and enter the
			kernel debugger at the earliest opportunity.

1579 1580 1581 1582
	kmac=		[MIPS] korina ethernet MAC address.
			Configure the RouterBoard 532 series on-chip
			Ethernet adapter MAC address.

1583 1584 1585 1586
	kmemleak=	[KNL] Boot-time kmemleak enable/disable
			Valid arguments: on, off
			Default: on

1587 1588 1589 1590 1591 1592 1593
	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)

1594
	kstack=N	[X86] Print N words from the kernel stack
1595 1596
			in oops dumps.

1597 1598 1599
	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
			Default is 0 (don't ignore, but inject #GP)

1600 1601
	kvm.mmu_audit=	[KVM] This is a R/W parameter which allows audit
			KVM MMU at runtime.
1602 1603 1604
			Default is 0 (off)

	kvm-amd.nested=	[KVM,AMD] Allow nested virtualization in KVM/SVM.
1605
			Default is 1 (enabled)
1606 1607 1608

	kvm-amd.npt=	[KVM,AMD] Disable nested paging (virtualized MMU)
			for all guests.
1609
			Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622

	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)

1623 1624 1625 1626
	kvm-intel.nested=
			[KVM,Intel] Enable VMX nesting (nVMX).
			Default is 0 (disabled)

1627 1628 1629 1630 1631 1632 1633 1634 1635
	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)

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	l2cr=		[PPC]

1638 1639
	l3cr=		[PPC]

1640
	lapic		[X86-32,APIC] Enable the local APIC even if BIOS
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			disabled it.
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1643 1644 1645 1646
	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.

1647
	lapic_timer_c2_ok	[X86,APIC] trust the local apic timer
1648
			in C2 power state.
1649

1650 1651 1652 1653
	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
1654
			libata.dma=4	  Compact Flash DMA only
1655 1656
			Combinations also work, so libata.dma=3 enables DMA
			for disks and CDROMs, but not CFs.
1657

1658 1659 1660
	libata.ignore_hpa=	[LIBATA] Ignore HPA limit
			libata.ignore_hpa=0	  keep BIOS limits (default)
			libata.ignore_hpa=1	  ignore limits, using full disk
1661

1662 1663 1664 1665
	libata.noacpi	[LIBATA] Disables use of ACPI in libata suspend/resume
			when set.
			Format: <int>

1666 1667
	libata.force=	[LIBATA] Force configurations.  The format is comma
			separated list of "[ID:]VAL" where ID is
1668
			PORT[.DEVICE].  PORT and DEVICE are decimal numbers
1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697
			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.

1698 1699 1700
			* nohrst, nosrst, norst: suppress hard, soft
                          and both resets.

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			* rstonce: only attempt one reset during
			  hot-unplug link recovery

1704 1705
			* dump_id: dump IDENTIFY data.

1706 1707
			* atapi_dmadir: Enable ATAPI DMADIR bridge support

1708 1709
			* disable: Disable this device.

1710 1711 1712
			If there are multiple matching configurations changing
			the same attribute, the last one is used.

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	memblock=debug	[KNL] Enable memblock debug messages.
1714

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	load_ramdisk=	[RAM] List of ramdisks to load from floppy
1716
			See Documentation/blockdev/ramdisk.txt.
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1718 1719
	lockd.nlm_grace_period=P  [NFS] Assign grace period.
			Format: <integer>
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1721 1722 1723 1724 1725 1726 1727 1728
	lockd.nlm_tcpport=N	[NFS] Assign TCP port.
			Format: <integer>

	lockd.nlm_timeout=T	[NFS] Assign timeout value.
			Format: <integer>

	lockd.nlm_udpport=M	[NFS] Assign UDP port.
			Format: <integer>
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1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772
	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.

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	logibm.irq=	[HW,MOUSE] Logitech Bus Mouse Driver
			Format: <irq>

	loglevel=	All Kernel Messages with a loglevel smaller than the
			console loglevel will be printed to the console. It can
			also be changed with klogd or other programs. The
			loglevels are defined as follows:

			0 (KERN_EMERG)		system is unusable
			1 (KERN_ALERT)		action must be taken immediately
			2 (KERN_CRIT)		critical conditions
			3 (KERN_ERR)		error conditions
			4 (KERN_WARNING)	warning conditions
			5 (KERN_NOTICE)		normal but significant condition
			6 (KERN_INFO)		informational
			7 (KERN_DEBUG)		debug-level messages

1790
	log_buf_len=n[KMG]	Sets the size of the printk ring buffer,
1791 1792 1793 1794 1795 1796
			in bytes.  n must be a power of two and greater
			than the minimal size. The minimal size is defined
			by LOG_BUF_SHIFT kernel config parameter. There is
			also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
			that allows to increase the default size depending on
			the number of CPUs. See init/Kconfig for more details.
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	logo.nologo	[FB] Disables display of the built-in Linux logo.
			This may be used to provide more screen space for
			kernel log messages and is useful when debugging
			kernel boot problems.

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	lp=0		[LP]	Specify parallel ports to use, e.g,
	lp=port[,port...]	lp=none,parport0 (lp0 not configured, lp1 uses
	lp=reset		first parallel port). 'lp=0' disables the
	lp=auto			printer driver. 'lp=reset' (which can be
				specified in addition to the ports) causes
				attached printers to be reset. Using
				lp=port1,port2,... specifies the parallel ports
				to associate lp devices with, starting with
				lp0. A port specification may be 'none' to skip
				that lp device, or a parport name such as
				'parport0'. Specifying 'lp=auto' instead of a
				port specification list means that device IDs
				from each port should be examined, to see if
				an IEEE 1284-compliant printer is attached; if
				so, the driver will manage that printer.
				See also header of drivers/char/lp.c.

	lpj=n		[KNL]
			Sets loops_per_jiffy to given constant, thus avoiding
			time-consuming boot-time autodetection (up to 250 ms per
			CPU). 0 enables autodetection (default). To determine
			the correct value for your kernel, boot with normal
			autodetection and see what value is printed. Note that
			on SMP systems the preset will be applied to all CPUs,
			which is likely to cause problems if your CPUs need
			significantly divergent settings. An incorrect value
			will cause delays in the kernel to be wrong, leading to
			unpredictable I/O errors and other breakage. Although
			unlikely, in the extreme case this might damage your
			hardware.

	ltpc=		[NET]
			Format: <io>,<irq>,<dma>

1837
	machvec=	[IA-64] Force the use of a particular machine-vector
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			(machvec) in a generic kernel.
			Example: machvec=hpzx1_swiotlb
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1841 1842 1843 1844
	machtype=	[Loongson] Share the same kernel image file between different
			 yeeloong laptop.
			Example: machtype=lemote-yeeloong-2f-7inch

1845 1846
	max_addr=nn[KMG]	[KNL,BOOT,ia64] All physical memory greater
			than or equal to this physical address is ignored.
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	maxcpus=	[SMP] Maximum number of processors that	an SMP kernel
1849 1850 1851 1852
			should make use of.  maxcpus=n : n >= 0 limits the
			kernel to using 'n' processors.  n=0 is a special case,
			it is equivalent to "nosmp", which also disables
			the IO APIC.
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1854 1855 1856 1857 1858 1859
	max_loop=	[LOOP] The number of loop block devices that get
	(loop.max_loop)	unconditionally pre-created at init time. The default
			number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
			of statically allocating a predefined number, loop
			devices can be requested on-demand with the
			/dev/loop-control interface.
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1861
	mce		[X86-32] Machine Check Exception
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	mce=option	[X86-64] See Documentation/x86/x86_64/boot-options.txt
1864

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	md=		[HW] RAID subsystems devices and level
			See Documentation/md.txt.
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	mdacon=		[MDA]
			Format: <first>,<last>
			Specifies range of consoles to be captured by the MDA.
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	mem=nn[KMG]	[KNL,BOOT] Force usage of a specific amount of memory
			Amount of memory to be used when the kernel is not able
			to see the whole system memory or for test.
1875 1876 1877 1878
			[X86] Work as limiting max address. Use together
			with memmap= to avoid physical address space collisions.
			Without memmap= PCI devices could be placed at addresses
			belonging to unused RAM.
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1880
	mem=nopentium	[BUGS=X86-32] Disable usage of 4MB pages for kernel
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			memory.

1883 1884 1885 1886
	memchunk=nn[KMG]
			[KNL,SH] Allow user to override the default size for
			per-device physically contiguous DMA buffers.

1887
	memmap=exactmap	[KNL,X86] Enable setting of an exact
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			E820 memory map, as specified by the user.
			Such memmap=exactmap lines can be constructed based on
			BIOS output or other requirements. See the memmap=nn@ss
			option description.

	memmap=nn[KMG]@ss[KMG]
1894 1895
			[KNL] Force usage of a specific region of memory.
			Region of memory to be used is from ss to ss+nn.
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	memmap=nn[KMG]#ss[KMG]
			[KNL,ACPI] Mark specific memory as ACPI data.
1899
			Region of memory to be marked is from ss to ss+nn.
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	memmap=nn[KMG]$ss[KMG]
			[KNL,ACPI] Mark specific memory as reserved.
1903
			Region of memory to be reserved is from ss to ss+nn.
1904 1905 1906 1907
			Example: Exclude memory from 0x18690000-0x1869ffff
			         memmap=64K$0x18690000
			         or
			         memmap=0x10000$0x18690000
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1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931
	memory_corruption_check=0/1 [X86]
			Some BIOSes seem to corrupt the first 64k of
			memory when doing things like suspend/resume.
			Setting this option will scan the memory
			looking for corruption.  Enabling this will
			both detect corruption and prevent the kernel
			from using the memory being corrupted.
			However, its intended as a diagnostic tool; if
			repeatable BIOS-originated corruption always
			affects the same memory, you can use memmap=
			to prevent the kernel from using that memory.

	memory_corruption_check_size=size [X86]
			By default it checks for corruption in the low
			64k, making this memory unavailable for normal
			use.  Use this parameter to scan for
			corruption in more or less memory.

	memory_corruption_check_period=seconds [X86]
			By default it checks for corruption every 60
			seconds.  Use this parameter to check at some
			other rate.  0 disables periodic checking.

1932
	memtest=	[KNL,X86] Enable memtest
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			Format: <integer>
			default : 0 <disable>
1935 1936 1937 1938 1939 1940
			Specifies the number of memtest passes to be
			performed. Each pass selects another test
			pattern from a given set of patterns. Memtest
			fills the memory with this pattern, validates
			memory contents and reserves bad memory
			regions that are detected.
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	meye.*=		[HW] Set MotionEye Camera parameters
			See Documentation/video4linux/meye.txt.

1945 1946 1947 1948
	mfgpt_irq=	[IA-32] Specify the IRQ to use for the
			Multi-Function General Purpose Timers on AMD Geode
			platforms.

1949 1950 1951 1952 1953
	mfgptfix	[X86-32] Fix MFGPT timers on AMD Geode platforms when
			the BIOS has incorrectly applied a workaround. TinyBIOS
			version 0.98 is known to be affected, 0.99 fixes the
			problem by letting the user disable the workaround.

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	mga=		[HW,DRM]

1956 1957 1958
	min_addr=nn[KMG]	[KNL,BOOT,ia64] All physical memory below this
			physical address is ignored.

1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979
	mini2440=	[ARM,HW,KNL]
			Format:[0..2][b][c][t]
			Default: "0tb"
			MINI2440 configuration specification:
			0 - The attached screen is the 3.5" TFT
			1 - The attached screen is the 7" TFT
			2 - The VGA Shield is attached (1024x768)
			Leaving out the screen size parameter will not load
			the TFT driver, and the framebuffer will be left
			unconfigured.
			b - Enable backlight. The TFT backlight pin will be
			linked to the kernel VESA blanking code and a GPIO
			LED. This parameter is not necessary when using the
			VGA shield.
			c - Enable the s3c camera interface.
			t - Reserved for enabling touchscreen support. The
			touchscreen support is not enabled in the mainstream
			kernel as of 2.6.30, a preliminary port can be found
			in the "bleeding edge" mini2440 support kernel at
			http://repo.or.cz/w/linux-2.6/mini2440.git

1980 1981 1982 1983 1984 1985 1986 1987
	mminit_loglevel=
			[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
			parameter allows control of the logging verbosity for
			the additional memory initialisation checks. A value
			of 0 disables mminit logging and a level of 4 will
			log everything. Information is printed at KERN_DEBUG
			so loglevel=8 may also need to be specified.

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	module.sig_enforce
			[KNL] When CONFIG_MODULE_SIG is set, this means that
			modules without (valid) signatures will fail to load.
1991
			Note that if CONFIG_MODULE_SIG_FORCE is set, that
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			is always true, so this option does nothing.

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	mousedev.tap_time=
			[MOUSE] Maximum time between finger touching and
			leaving touchpad surface for touch to be considered
			a tap and be reported as a left button click (for
			touchpads working in absolute mode only).
			Format: <msecs>
	mousedev.xres=	[MOUSE] Horizontal screen resolution, used for devices
			reporting absolute coordinates, such as tablets
	mousedev.yres=	[MOUSE] Vertical screen resolution, used for devices
			reporting absolute coordinates, such as tablets

2005
	movablecore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
2006 2007 2008 2009 2010 2011 2012 2013 2014
			is similar to kernelcore except it specifies the
			amount of memory used for migratable allocations.
			If both kernelcore and movablecore is specified,
			then kernelcore will be at *least* the specified
			value but may be more. If movablecore on its own
			is specified, the administrator must be careful
			that the amount of memory usable for all allocations
			is not too small.

2015 2016 2017
	movable_node	[KNL,X86] Boot-time switch to enable the effects
			of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.

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	MTD_Partition=	[MTD]
			Format: <name>,<region-number>,<size>,<offset>

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2021 2022
	MTD_Region=	[MTD] Format:
			<name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
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	mtdparts=	[MTD]
2025
			See drivers/mtd/cmdlinepart.c.
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2027 2028 2029 2030
	multitce=off	[PPC]  This parameter disables the use of the pSeries
			firmware feature for updating multiple TCE entries
			at a time.

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2031 2032 2033 2034 2035 2036 2037 2038 2039 2040
	onenand.bdry=	[HW,MTD] Flex-OneNAND Boundary Configuration

			Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]

			boundary - index of last SLC block on Flex-OneNAND.
				   The remaining blocks are configured as MLC blocks.
			lock	 - Configure if Flex-OneNAND boundary should be locked.
				   Once locked, the boundary cannot be changed.
				   1 indicates lock status, 0 indicates unlock status.

2041 2042 2043 2044 2045
	mtdset=		[ARM]
			ARM/S3C2412 JIVE boot control

			See arch/arm/mach-s3c2412/mach-jive.c

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	mtouchusb.raw_coordinates=
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2047 2048
			[HW] Make the MicroTouch USB driver use raw coordinates
			('y', default) or cooked coordinates ('n')
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Linus Torvalds 已提交
2049

2050
	mtrr_chunk_size=nn[KMG] [X86]
2051
			used for mtrr cleanup. It is largest continuous chunk
2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066
			that could hold holes aka. UC entries.

	mtrr_gran_size=nn[KMG] [X86]
			Used for mtrr cleanup. It is granularity of mtrr block.
			Default is 1.
			Large value could prevent small alignment from
			using up MTRRs.

	mtrr_spare_reg_nr=n [X86]
			Format: <integer>
			Range: 0,7 : spare reg number
			Default : 1
			Used for mtrr cleanup. It is spare mtrr entries number.
			Set to 2 or more if your graphical card needs more.

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	n2=		[NET] SDL Inc. RISCom/N2 synchronous serial card

	netdev=		[NET] Network devices parameters
			Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
			Note that mem_start is often overloaded to mean
			something different and driver-specific.
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			This usage is only documented in each driver source
			file if at all.

2076 2077 2078 2079
	nf_conntrack.acct=
			[NETFILTER] Enable connection tracking flow accounting
			0 to disable accounting
			1 to enable accounting
2080
			Default value is 0.
2081

2082
	nfsaddrs=	[NFS] Deprecated.  Use ip= instead.
2083
			See Documentation/filesystems/nfs/nfsroot.txt.
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	nfsroot=	[NFS] nfs root filesystem for disk-less boxes.
2086
			See Documentation/filesystems/nfs/nfsroot.txt.
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2088 2089 2090
	nfsrootdebug	[NFS] enable nfsroot debugging messages.
			See Documentation/filesystems/nfs/nfsroot.txt.

2091 2092 2093 2094
	nfs.callback_tcpport=
			[NFS] set the TCP port on which the NFSv4 callback
			channel should listen.

2095 2096 2097 2098 2099 2100 2101 2102
	nfs.cache_getent=
			[NFS] sets the pathname to the program which is used
			to update the NFS client cache entries.

	nfs.cache_getent_timeout=
			[NFS] sets the timeout after which an attempt to
			update a cache entry is deemed to have failed.

2103 2104 2105 2106
	nfs.idmap_cache_timeout=
			[NFS] set the maximum lifetime for idmapper cache
			entries.

2107 2108 2109 2110 2111 2112 2113
	nfs.enable_ino64=
			[NFS] enable 64-bit inode numbers.
			If zero, the NFS client will fake up a 32-bit inode
			number for the readdir() and stat() syscalls instead
			of returning the full 64-bit number.
			The default is to return 64-bit inode numbers.

2114 2115 2116 2117 2118 2119 2120 2121
	nfs.max_session_slots=
			[NFSv4.1] Sets the maximum number of session slots
			the client will attempt to negotiate with the server.
			This limits the number of simultaneous RPC requests
			that the client can send to the NFSv4.1 server.
			Note that there is little point in setting this
			value higher than the max_tcp_slot_table_limit.

2122
	nfs.nfs4_disable_idmapping=
2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133
			[NFSv4] When set to the default of '1', this option
			ensures that both the RPC level authentication
			scheme and the NFS level operations agree to use
			numeric uids/gids if the mount is using the
			'sec=sys' security flavour. In effect it is
			disabling idmapping, which can make migration from
			legacy NFSv2/v3 systems to NFSv4 easier.
			Servers that do not support this mode of operation
			will be autodetected by the client, and it will fall
			back to using the idmapper.
			To turn off this behaviour, set the value to '0'.
2134 2135 2136 2137 2138
	nfs.nfs4_unique_id=
			[NFS4] Specify an additional fixed unique ident-
			ification string that NFSv4 clients can insert into
			their nfs_client_id4 string.  This is typically a
			UUID that is generated at system install time.
2139

2140 2141 2142 2143 2144 2145 2146
	nfs.send_implementation_id =
			[NFSv4.1] Send client implementation identification
			information in exchange_id requests.
			If zero, no implementation identification information
			will be sent.
			The default is to send the implementation identification
			information.
2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158
	
	nfs.recover_lost_locks =
			[NFSv4] Attempt to recover locks that were lost due
			to a lease timeout on the server. Please note that
			doing this risks data corruption, since there are
			no guarantees that the file will remain unchanged
			after the locks are lost.
			If you want to enable the kernel legacy behaviour of
			attempting to recover these locks, then set this
			parameter to '1'.
			The default parameter value of '0' causes the kernel
			not to attempt recovery of lost locks.
2159

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	nfsd.nfs4_disable_idmapping=
			[NFSv4] When set to the default of '1', the NFSv4
			server will return only numeric uids and gids to
			clients using auth_sys, and will accept numeric uids
			and gids from such clients.  This is intended to ease
			migration from NFSv2/v3.
2166

2167 2168 2169 2170 2171 2172
	objlayoutdriver.osd_login_prog=
			[NFS] [OBJLAYOUT] sets the pathname to the program which
			is used to automatically discover and login into new
			osd-targets. Please see:
			Documentation/filesystems/pnfs.txt for more explanations

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	nmi_debug=	[KNL,AVR32,SH] Specify one or more actions to take
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2174 2175 2176
			when a NMI is triggered.
			Format: [state][,regs][,debounce][,die]

2177
	nmi_watchdog=	[KNL,BUGS=X86] Debugging features for SMP kernels
2178
			Format: [panic,][nopanic,][num]
2179
			Valid num: 0
2180
			0 - turn nmi_watchdog off
2181
			When panic is specified, panic when an NMI watchdog
2182 2183
			timeout occurs (or 'nopanic' to override the opposite
			default).
2184 2185
			This is useful when you use a panic=... timeout and
			need the box quickly up again.
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2187 2188 2189 2190 2191
	netpoll.carrier_timeout=
			[NET] Specifies amount of time (in seconds) that
			netpoll should wait for a carrier. By default netpoll
			waits 4 seconds.

2192
	no387		[BUGS=X86-32] Tells the kernel to use the 387 maths
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2193 2194 2195
			emulation library even if a 387 maths coprocessor
			is present.

2196 2197 2198 2199 2200 2201 2202 2203 2204
	no_console_suspend
			[HW] Never suspend the console
			Disable suspending of consoles during suspend and
			hibernate operations.  Once disabled, debugging
			messages can reach various consoles while the rest
			of the system is being put to sleep (ie, while
			debugging driver suspend/resume hooks).  This may
			not work reliably with all consoles, but is known
			to work with serial and VGA consoles.
2205 2206 2207 2208 2209
			To facilitate more flexible debugging, we also add
			console_suspend, a printk module parameter to control
			it. Users could use console_suspend (usually
			/sys/module/printk/parameters/console_suspend) to
			turn on/off it dynamically.
2210

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2211 2212 2213
	noaliencache	[MM, NUMA, SLAB] Disables the allocation of alien
			caches in the slab allocator.  Saves per-node memory,
			but will impact performance.
2214

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2215 2216
	noalign		[KNL,ARM]

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2217 2218 2219
	noapic		[SMP,APIC] Tells the kernel to not make use of any
			IOAPICs that may be present in the system.

2220 2221
	noautogroup	Disable scheduler automatic task group creation.

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	nobats		[PPC] Do not use BATs for mapping kernel lowmem
			on "Classic" PPC cores.

	nocache		[ARM]
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Randy Dunlap 已提交
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2227 2228
	noclflush	[BUGS=X86] Don't use the CLFLUSH instruction

2229 2230
	nodelayacct	[KNL] Disable per-task delay accounting

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2231 2232
	nodisconnect	[HW,SCSI,M68K] Disables SCSI disconnects.

2233 2234
	nodsp		[SH] Disable hardware DSP at boot time.

2235
	noefi		[X86] Disable EFI runtime services support.
2236

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2237 2238
	noexec		[IA-64]

2239
	noexec		[X86]
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2240
			On X86-32 available only on PAE configured kernels.
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2241
			noexec=on: enable non-executable mappings (default)
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Jiri Slaby 已提交
2242 2243
			noexec=off: disable non-executable mappings

2244 2245 2246 2247
	nosmap		[X86]
			Disable SMAP (Supervisor Mode Access Prevention)
			even if it is supported by processor.

2248
	nosmep		[X86]
2249
			Disable SMEP (Supervisor Mode Execution Prevention)
2250 2251
			even if it is supported by processor.

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2252 2253 2254 2255 2256 2257
	noexec32	[X86-64]
			This affects only 32-bit executables.
			noexec32=on: enable non-executable mappings (default)
				read doesn't imply executable mappings
			noexec32=off: disable non-executable mappings
				read implies executable mappings
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2259 2260
	nofpu		[SH] Disable hardware FPU at boot time.

2261
	nofxsr		[BUGS=X86-32] Disables x86 floating point extended
2262 2263
			register save and restore. The kernel will only save
			legacy floating-point registers on task switch.
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2265 2266 2267 2268
	noxsave		[BUGS=X86] Disables x86 extended register state save
			and restore using xsave. The kernel will fallback to
			enabling legacy floating-point and sse state.

2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283
	noxsaveopt	[X86] Disables xsaveopt used in saving x86 extended
			register states. The kernel will fall back to use
			xsave to save the states. By using this parameter,
			performance of saving the states is degraded because
			xsave doesn't support modified optimization while
			xsaveopt supports it on xsaveopt enabled systems.

	noxsaves	[X86] Disables xsaves and xrstors used in saving and
			restoring x86 extended register state in compacted
			form of xsave area. The kernel will fall back to use
			xsaveopt and xrstor to save and restore the states
			in standard form of xsave area. By using this
			parameter, xsave area per process might occupy more
			memory on xsaves enabled systems.

2284
	eagerfpu=	[X86]
2285
			on	enable eager fpu restore
2286
			off	disable eager fpu restore
2287 2288
			auto	selects the default scheme, which automatically
				enables eagerfpu restore for xsaveopt.
2289

2290 2291 2292
	nohlt		[BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
			wfi(ARM) instruction doesn't work correctly and not to
			use it. This is also useful when using JTAG debugger.
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2294 2295 2296 2297
	no_file_caps	Tells the kernel not to honor file capabilities.  The
			only way then for a file to be executed with privilege
			is to be setuid root or executed by root.

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2298 2299 2300 2301 2302 2303 2304
	nohalt		[IA-64] Tells the kernel not to use the power saving
			function PAL_HALT_LIGHT when idle. This increases
			power-consumption. On the positive side, it reduces
			interrupt wake-up latency, which may improve performance
			in certain environments such as networked servers or
			real-time systems.

2305 2306
	nohibernate	[HIBERNATION] Disable hibernation and resume.

2307 2308 2309 2310
	nohz=		[KNL] Boottime enable/disable dynamic ticks
			Valid arguments: on, off
			Default: on

2311 2312
	nohz_full=	[KNL,BOOT]
			In kernels built with CONFIG_NO_HZ_FULL=y, set
2313
			the specified list of CPUs whose tick will be stopped
2314 2315
			whenever possible. The boot CPU will be forced outside
			the range to maintain the timekeeping.
2316 2317
			The CPUs in this range must also be included in the
			rcu_nocbs= set.
2318

2319 2320
	noiotrap	[SH] Disables trapped I/O port accesses.

2321
	noirqdebug	[X86-32] Disables the code which attempts to detect and
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2322 2323
			disable unhandled interrupt sources.

2324
	no_timer_check	[X86,APIC] Disables the code which tests for
2325 2326
			broken timer IRQ sources.

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2327 2328 2329 2330 2331
	noisapnp	[ISAPNP] Disables ISA PnP code.

	noinitrd	[RAM] Tells the kernel not to load any configured
			initial RAM disk.

2332 2333
	nointremap	[X86-64, Intel-IOMMU] Do not enable interrupt
			remapping.
2334
			[Deprecated - use intremap=off]
2335

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2336 2337
	nointroute	[IA-64]

2338
	nojitter	[IA-64] Disables jitter checking for ITC timers.
2339

2340 2341
	no-kvmclock	[X86,KVM] Disable paravirtualized KVM clock driver

2342 2343 2344
	no-kvmapf	[X86,KVM] Disable paravirtualized asynchronous page
			fault handling.

2345 2346 2347 2348
	no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
			steal time is computed, but won't influence scheduler
			behaviour

2349
	nolapic		[X86-32,APIC] Do not enable or use the local APIC.
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2350

2351
	nolapic_timer	[X86-32,APIC] Do not use the local APIC timer.
2352

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2353 2354 2355
	noltlbs		[PPC] Do not use large page/tlb entries for kernel
			lowmem mapping on PPC40x.

2356 2357
	nomca		[IA-64] Disable machine check abort handling

2358
	nomce		[X86-32] Machine Check Exception
2359

2360 2361 2362
	nomfgpt		[X86-32] Disable Multi-Function General Purpose
			Timer usage (for AMD Geode machines).

2363 2364 2365 2366
	nonmi_ipi	[X86] Disable using NMI IPIs during panic/reboot to
			shutdown the other cpus.  Instead use the REBOOT_VECTOR
			irq.

2367 2368
	nomodule	Disable module load

2369 2370 2371
	nopat		[X86] Disable PAT (page attribute table extension of
			pagetables) support.

2372 2373 2374
	norandmaps	Don't use address space randomization.  Equivalent to
			echo 0 > /proc/sys/kernel/randomize_va_space

2375
	noreplace-paravirt	[X86,IA-64,PV_OPS] Don't patch paravirt_ops
2376

2377
	noreplace-smp	[X86-32,SMP] Don't replace SMP instructions
2378 2379
			with UP alternatives

2380 2381 2382 2383
	nordrand	[X86] Disable kernel use of the RDRAND and
			RDSEED instructions even if they are supported
			by the processor.  RDRAND and RDSEED are still
			available to user space applications.
2384

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2385 2386 2387
	noresume	[SWSUSP] Disables resume and restores original swap
			space.

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2388 2389 2390 2391 2392 2393
	no-scroll	[VGA] Disables scrollback.
			This is required for the Braillex ib80-piezo Braille
			reader made by F.H. Papenmeier (Germany).

	nosbagart	[IA-64]

2394
	nosep		[BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2395

2396 2397
	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel,
			and disable the IO APIC.  legacy for "maxcpus=0".
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2398

2399 2400
	nosoftlockup	[KNL] Disable the soft-lockup detector.

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2401 2402
	nosync		[HW,M68K] Disables sync negotiation for all devices.

2403
	notsc		[BUGS=X86-32] Disable Time Stamp Counter
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2404 2405 2406

	nousb		[USB] Disable the USB subsystem

2407
	nowatchdog	[KNL] Disable the lockup detector (NMI watchdog).
2408

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2409
	nowb		[ARM]
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Randy Dunlap 已提交
2410

2411 2412
	nox2apic	[X86-64,APIC] Do not enable x2APIC mode.

2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426
	cpu0_hotplug	[X86] Turn on CPU0 hotplug feature when
			CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
			Some features depend on CPU0. Known dependencies are:
			1. Resume from suspend/hibernate depends on CPU0.
			Suspend/hibernate will fail if CPU0 is offline and you
			need to online CPU0 before suspend/hibernate.
			2. PIC interrupts also depend on CPU0. CPU0 can't be
			removed if a PIC interrupt is detected.
			It's said poweroff/reboot may depend on CPU0 on some
			machines although I haven't seen such issues so far
			after CPU0 is offline on a few tested machines.
			If the dependencies are under your control, you can
			turn on cpu0_hotplug.

2427
	nptcg=		[IA-64] Override max number of concurrent global TLB
2428 2429 2430
			purges which is reported from either PAL_VM_SUMMARY or
			SAL PALO.

2431 2432 2433 2434 2435 2436
	nr_cpus=	[SMP] Maximum number of processors that	an SMP kernel
			could support.  nr_cpus=n : n >= 1 limits the kernel to
			supporting 'n' processors. Later in runtime you can not
			use hotplug cpu feature to put more cpu back to online.
			just like you compile the kernel NR_CPUS=n

2437 2438
	nr_uarts=	[SERIAL] maximum number of UARTs to be registered.

2439 2440 2441
	numa_balancing=	[KNL,X86] Enable or disable automatic NUMA balancing.
			Allowed values are enable and disable

2442 2443 2444 2445 2446
	numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
			one of ['zone', 'node', 'default'] can be specified
			This can be set from sysctl after boot.
			See Documentation/sysctl/vm.txt for details.

2447 2448 2449 2450
	ohci1394_dma=early	[HW] enable debugging via the ohci1394 driver.
			See Documentation/debugging-via-ohci1394.txt for more
			info.

2451 2452 2453 2454 2455 2456 2457
	olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
			Rather than timing out after 20 ms if an EC
			command is not properly ACKed, override the length
			of the timeout.  We have interrupts disabled while
			waiting for the ACK, so if this is set too high
			interrupts *may* be lost!

2458 2459 2460 2461 2462
	omap_mux=	[OMAP] Override bootloader pin multiplexing.
			Format: <mux_mode0.mode_name=value>...
			For example, to override I2C bus2:
			omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100

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2463 2464 2465
	oprofile.timer=	[HW]
			Use timer interrupt instead of performance counters

2466 2467 2468
	oprofile.cpu_type=	Force an oprofile cpu type
			This might be useful if you have an older oprofile
			userland or if you want common events.
2469 2470
			Format: { arch_perfmon }
			arch_perfmon: [X86] Force use of architectural
2471 2472
				perfmon on Intel CPUs instead of the
				CPU specific event set.
2473 2474 2475
			timer: [X86] Force use of architectural NMI
				timer mode (see also oprofile.timer
				for generic hr timer mode)
2476 2477
				[s390] Force legacy basic mode sampling
                                (report cpu_type "timer")
2478

2479 2480 2481
	oops=panic	Always panic on oopses. Default is to just kill the
			process, but there is a small probability of
			deadlocking the machine.
2482 2483 2484
			This will also cause panics on machine check exceptions.
			Useful together with panic=30 to trigger a reboot.

2485 2486 2487
	OSS		[HW,OSS]
			See Documentation/sound/oss/oss-parameters.txt

2488
	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
2489 2490 2491
			timeout > 0: seconds before rebooting
			timeout = 0: wait forever
			timeout < 0: reboot immediately
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2492 2493
			Format: <timeout>

2494 2495 2496 2497 2498 2499 2500 2501
	crash_kexec_post_notifiers
			Run kdump after running panic-notifiers and dumping
			kmsg. This only for the users who doubt kdump always
			succeeds in any situation.
			Note that this also increases risks of kdump failure,
			because some panic notifiers can make the crashed
			kernel more unstable.

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	parkbd.port=	[HW] Parallel port number the keyboard adapter is
			connected to, default is 0.
			Format: <parport#>
	parkbd.mode=	[HW] Parallel port keyboard adapter mode of operation,
			0 for XT, 1 for AT (default is AT).
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2507 2508 2509 2510 2511 2512 2513 2514 2515 2516 2517 2518 2519 2520 2521 2522 2523 2524 2525 2526 2527 2528
			Format: <mode>

	parport=	[HW,PPT] Specify parallel ports. 0 disables.
			Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
			Use 'auto' to force the driver to use any
			IRQ/DMA settings detected (the default is to
			ignore detected IRQ/DMA settings because of
			possible conflicts). You can specify the base
			address, IRQ, and DMA settings; IRQ and DMA
			should be numbers, or 'auto' (for using detected
			settings on that particular port), or 'nofifo'
			(to avoid using a FIFO even if it is detected).
			Parallel ports are assigned in the order they
			are specified on the command line, starting
			with parport0.

	parport_init_mode=	[HW,PPT]
			Configure VIA parallel port to operate in
			a specific mode. This is necessary on Pegasos
			computer where firmware has no options for setting
			up parallel port mode and sets it to spp.
			Currently this function knows 686a and 8231 chips.
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			Format: [spp|ps2|epp|ecp|ecpepp]

2531 2532 2533 2534 2535
	pause_on_oops=
			Halt all CPUs after the first oops has been printed for
			the specified number of seconds.  This is to be used if
			your oopses keep scrolling off the screen.

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	pcbit=		[HW,ISDN]

	pcd.		[PARIDE]
			See header of drivers/block/paride/pcd.c.
2540
			See also Documentation/blockdev/paride.txt.
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	pci=option[,option...]	[PCI] various PCI subsystem options:
2543 2544
		earlydump	[X86] dump PCI config space before the kernel
			        changes anything
2545
		off		[X86] don't probe for the PCI bus
2546
		bios		[X86-32] force use of PCI BIOS, don't access
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2547 2548
				the hardware directly. Use this if your machine
				has a non-standard PCI host bridge.
2549
		nobios		[X86-32] disallow use of PCI BIOS, only direct
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2550 2551 2552
				hardware access methods are allowed. Use this
				if you experience crashes upon bootup and you
				suspect they are caused by the BIOS.
2553
		conf1		[X86] Force use of PCI Configuration
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				Mechanism 1.
2555
		conf2		[X86] Force use of PCI Configuration
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2556
				Mechanism 2.
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2557 2558 2559
		noaer		[PCIE] If the PCIEAER kernel config parameter is
				enabled, this kernel boot option can be used to
				disable the use of PCIE advanced error reporting.
2560 2561
		nodomains	[PCI] Disable support for multiple PCI
				root domains (aka PCI segments, in ACPI-speak).
2562
		nommconf	[X86] Disable use of MMCONFIG for PCI
2563
				Configuration
2564 2565 2566
		check_enable_amd_mmconf [X86] check for and enable
				properly configured MMIO access to PCI
				config space on AMD family 10h CPU
2567 2568 2569
		nomsi		[MSI] If the PCI_MSI kernel config parameter is
				enabled, this kernel boot option can be used to
				disable the use of MSI interrupts system-wide.
2570 2571 2572
		noioapicquirk	[APIC] Disable all boot interrupt quirks.
				Safety option to keep boot IRQs enabled. This
				should never be necessary.
2573 2574 2575 2576
		ioapicreroute	[APIC] Enable rerouting of boot IRQs to the
				primary IO-APIC for bridges that cannot disable
				boot IRQs. This fixes a source of spurious IRQs
				when the system masks IRQs.
2577 2578 2579 2580
		noioapicreroute	[APIC] Disable workaround that uses the
				boot IRQ equivalent of an IRQ that connects to
				a chipset where boot IRQs cannot be disabled.
				The opposite of ioapicreroute.
2581
		biosirq		[X86-32] Use PCI BIOS calls to get the interrupt
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2582 2583 2584 2585 2586 2587 2588
				routing table. These calls are known to be buggy
				on several machines and they hang the machine
				when used, but on other computers it's the only
				way to get the interrupt routing table. Try
				this option if the kernel is unable to allocate
				IRQs or discover secondary PCI buses on your
				motherboard.
2589
		rom		[X86] Assign address space to expansion ROMs.
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2590 2591 2592
				Use with caution as certain devices share
				address decoders between ROMs and other
				resources.
2593
		norom		[X86] Do not assign address space to
2594 2595
				expansion ROMs that do not already have
				BIOS assigned address ranges.
2596 2597
		nobar		[X86] Do not assign address space to the
				BARs that weren't assigned by the BIOS.
2598
		irqmask=0xMMMM	[X86] Set a bit mask of IRQs allowed to be
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2599 2600 2601
				assigned automatically to PCI devices. You can
				make the kernel exclude IRQs of your ISA cards
				this way.
2602
		pirqaddr=0xAAAAA	[X86] Specify the physical address
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2603 2604 2605
				of the PIRQ table (normally generated
				by the BIOS) if it is outside the
				F0000h-100000h range.
2606
		lastbus=N	[X86] Scan all buses thru bus #N. Can be
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2607 2608 2609
				useful if the kernel is unable to find your
				secondary buses and you want to tell it
				explicitly which ones they are.
2610
		assign-busses	[X86] Always assign all PCI bus
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				numbers ourselves, overriding
				whatever the firmware may have done.
2613
		usepirqmask	[X86] Honor the possible IRQ mask stored
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2614 2615 2616 2617 2618
				in the BIOS $PIR table. This is needed on
				some systems with broken BIOSes, notably
				some HP Pavilion N5400 and Omnibook XE3
				notebooks. This will have no effect if ACPI
				IRQ routing is enabled.
2619
		noacpi		[X86] Do not use ACPI for IRQ routing
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				or for PCI scanning.
2621 2622 2623 2624 2625 2626
		use_crs		[X86] Use PCI host bridge window information
				from ACPI.  On BIOSes from 2008 or later, this
				is enabled by default.  If you need to use this,
				please report a bug.
		nocrs		[X86] Ignore PCI host bridge windows from ACPI.
			        If you need to use this, please report a bug.
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2627 2628 2629 2630
		routeirq	Do IRQ routing for all PCI devices.
				This is normally done in pci_enable_device(),
				so this option is a temporary workaround
				for broken drivers that don't call it.
2631 2632
		skip_isa_align	[X86] do not align io start addr, so can
				handle more pci cards
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2633 2634 2635 2636 2637
		firmware	[ARM] Do not re-enumerate the bus but instead
				just use the configuration from the
				bootloader. This is currently used on
				IXP2000 systems where the bus has to be
				configured a certain way for adjunct CPUs.
2638 2639 2640 2641 2642
		noearly		[X86] Don't do any early type 1 scanning.
				This might help on some broken boards which
				machine check when some devices' config space
				is read. But various workarounds are disabled
				and some IOMMU drivers will not work.
2643 2644 2645 2646
		bfsort		Sort PCI devices into breadth-first order.
				This sorting is done to get a device
				order compatible with older (<= 2.4) kernels.
		nobfsort	Don't sort PCI devices into breadth-first order.
2647 2648 2649 2650 2651 2652 2653 2654 2655 2656 2657 2658 2659 2660 2661
		pcie_bus_tune_off	Disable PCIe MPS (Max Payload Size)
				tuning and use the BIOS-configured MPS defaults.
		pcie_bus_safe	Set every device's MPS to the largest value
				supported by all devices below the root complex.
		pcie_bus_perf	Set device MPS to the largest allowable MPS
				based on its parent bus. Also set MRRS (Max
				Read Request Size) to the largest supported
				value (no larger than the MPS that the device
				or bus can support) for best performance.
		pcie_bus_peer2peer	Set every device's MPS to 128B, which
				every device is guaranteed to support. This
				configuration allows peer-to-peer DMA between
				any pair of devices, possibly at the cost of
				reduced performance.  This also guarantees
				that hot-added devices will work.
2662 2663 2664 2665 2666 2667
		cbiosize=nn[KMG]	The fixed amount of bus space which is
				reserved for the CardBus bridge's IO window.
				The default value is 256 bytes.
		cbmemsize=nn[KMG]	The fixed amount of bus space which is
				reserved for the CardBus bridge's memory
				window. The default value is 64 megabytes.
2668 2669 2670 2671 2672 2673 2674 2675 2676
		resource_alignment=
				Format:
				[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
				Specifies alignment and device to reassign
				aligned memory resources.
				If <order of align> is not specified,
				PAGE_SIZE is used as alignment.
				PCI-PCI bridge can be specified, if resource
				windows need to be expanded.
2677 2678 2679 2680 2681 2682
		ecrc=		Enable/disable PCIe ECRC (transaction layer
				end-to-end CRC checking).
				bios: Use BIOS/firmware settings. This is the
				the default.
				off: Turn ECRC off
				on: Turn ECRC on.
2683 2684 2685 2686 2687 2688
		hpiosize=nn[KMG]	The fixed amount of bus space which is
				reserved for hotplug bridge's IO window.
				Default size is 256 bytes.
		hpmemsize=nn[KMG]	The fixed amount of bus space which is
				reserved for hotplug bridge's memory window.
				Default size is 2 megabytes.
2689 2690 2691 2692 2693 2694 2695
		realloc=	Enable/disable reallocating PCI bridge resources
				if allocations done by BIOS are too small to
				accommodate resources required by all child
				devices.
				off: Turn realloc off
				on: Turn realloc on
		realloc		same as realloc=on
2696
		noari		do not use PCIe ARI.
2697 2698 2699
		pcie_scan_all	Scan all possible PCIe devices.  Otherwise we
				only look for one device below a PCIe downstream
				port.
2700

2701 2702 2703 2704 2705 2706
	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
			Management.
		off	Disable ASPM.
		force	Enable ASPM even on devices that claim not to support it.
			WARNING: Forcing ASPM on may cause system lockups.

2707 2708 2709 2710
	pcie_hp=	[PCIE] PCI Express Hotplug driver options:
		nomsi	Do not use MSI for PCI Express Native Hotplug (this
			makes all PCIe ports use INTx for hotplug services).

2711
	pcie_ports=	[PCIE] PCIe ports handling:
2712 2713 2714 2715 2716
		auto	Ask the BIOS whether or not to use native PCIe services
			associated with PCIe ports (PME, hot-plug, AER).  Use
			them only if that is allowed by the BIOS.
		native	Use native PCIe services associated with PCIe ports
			unconditionally.
2717 2718 2719
		compat	Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
			ports driver.

2720
	pcie_pme=	[PCIE,PM] Native PCIe PME signaling options:
2721
		nomsi	Do not use MSI for native PCIe PME signaling (this makes
2722
			all PCIe root ports use INTx for all services).
2723

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2724 2725
	pcmv=		[HW,PCMCIA] BadgePAD 4

2726 2727 2728 2729 2730 2731 2732
	pd_ignore_unused
			[PM]
			Keep all power-domains already enabled by bootloader on,
			even if no driver has claimed them. This is useful
			for debug and development, but should not be
			needed on a platform with proper driver support.

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2733
	pd.		[PARIDE]
2734
			See Documentation/blockdev/paride.txt.
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2735 2736 2737 2738 2739 2740

	pdcchassis=	[PARISC,HW] Disable/Enable PDC Chassis Status codes at
			boot time.
			Format: { 0 | 1 }
			See arch/parisc/kernel/pdc_chassis.c

2741
	percpu_alloc=	Select which percpu first chunk allocator to use.
2742 2743 2744 2745 2746
			Currently supported values are "embed" and "page".
			Archs may support subset or none of the	selections.
			See comments in mm/percpu.c for details on each
			allocator.  This parameter is primarily	for debugging
			and performance comparison.
2747

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2748
	pf.		[PARIDE]
2749
			See Documentation/blockdev/paride.txt.
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2750 2751

	pg.		[PARIDE]
2752
			See Documentation/blockdev/paride.txt.
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2753 2754

	pirq=		[SMP,APIC] Manual mp-table setup
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2755
			See Documentation/x86/i386/IO-APIC.txt.
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2756 2757 2758 2759 2760

	plip=		[PPT,NET] Parallel port network link
			Format: { parport<nr> | timid | 0 }
			See also Documentation/parport.txt.

2761
	pmtmr=		[X86] Manual setup of pmtmr I/O Port.
2762 2763 2764
			Override pmtimer IOPort with a hex value.
			e.g. pmtmr=0x508

2765 2766 2767 2768 2769 2770
	pnp.debug=1	[PNP]
			Enable PNP debug messages (depends on the
			CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
			via /sys/module/pnp/parameters/debug.  We always show
			current resource usage; turning this on also shows
			possible settings and some assignment information.
2771

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2772 2773 2774 2775 2776 2777 2778 2779 2780 2781 2782 2783 2784
	pnpacpi=	[ACPI]
			{ off }

	pnpbios=	[ISAPNP]
			{ on | off | curr | res | no-curr | no-res }

	pnp_reserve_irq=
			[ISAPNP] Exclude IRQs for the autoconfiguration

	pnp_reserve_dma=
			[ISAPNP] Exclude DMAs for the autoconfiguration

	pnp_reserve_io=	[ISAPNP] Exclude I/O ports for the autoconfiguration
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2785
			Ranges are in pairs (I/O port base and size).
L
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2786 2787

	pnp_reserve_mem=
R
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2788 2789
			[ISAPNP] Exclude memory regions for the
			autoconfiguration.
L
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2790 2791
			Ranges are in pairs (memory base and size).

2792 2793 2794 2795 2796 2797
	ports=		[IP_VS_FTP] IPVS ftp helper module
			Default is 21.
			Up to 8 (IP_VS_APP_MAX_PORTS) ports
			may be specified.
			Format: <port>,<port>....

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2798 2799
	print-fatal-signals=
			[KNL] debug: print fatal signals
2800 2801 2802 2803 2804 2805 2806 2807 2808

			If enabled, warn about various signal handling
			related application anomalies: too many signals,
			too many POSIX.1 timers, fatal signals causing a
			coredump - etc.

			If you hit the warning due to signal overflow,
			you might want to try "ulimit -i unlimited".

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Ingo Molnar 已提交
2809 2810
			default: off.

2811 2812 2813 2814 2815 2816
	printk.always_kmsg_dump=
			Trigger kmsg_dump for cases other than kernel oops or
			panics
			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
			default: disabled

2817 2818 2819
	printk.time=	Show timing data prefixed to each printk message line
			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)

2820 2821 2822 2823 2824 2825 2826 2827
	processor.max_cstate=	[HW,ACPI]
			Limit processor to maximum C-state
			max_cstate=9 overrides any DMI blacklist limit.

	processor.nocst	[HW,ACPI]
			Ignore the _CST method to determine C-states,
			instead using the legacy FADT method

L
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2828
	profile=	[KNL] Enable kernel profiling via /proc/profile
R
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2829 2830 2831 2832
			Format: [schedule,]<number>
			Param: "schedule" - profile schedule points.
			Param: <number> - step/bucket size as a power of 2 for
				statistical time based profiling.
2833 2834
			Param: "sleep" - profile D-state sleeping (millisecs).
				Requires CONFIG_SCHEDSTATS
2835
			Param: "kvm" - profile VM exits.
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2836 2837 2838

	prompt_ramdisk=	[RAM] List of RAM disks to prompt for floppy disk
			before loading.
2839
			See Documentation/blockdev/ramdisk.txt.
L
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2840

R
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2841 2842
	psmouse.proto=	[HW,MOUSE] Highest PS2 mouse protocol extension to
			probe for; one of (bare|imps|exps|lifebook|any).
L
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2843 2844
	psmouse.rate=	[HW,MOUSE] Set desired mouse report rate, in reports
			per second.
R
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2845 2846
	psmouse.resetafter=	[HW,MOUSE]
			Try to reset the device after so many bad packets
L
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2847 2848 2849 2850
			(0 = never).
	psmouse.resolution=
			[HW,MOUSE] Set desired mouse resolution, in dpi.
	psmouse.smartscroll=
R
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2851
			[HW,MOUSE] Controls Logitech smartscroll autorepeat.
L
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2852 2853
			0 = disabled, 1 = enabled (default).

2854 2855
	pstore.backend=	Specify the name of the pstore backend to use

L
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2856
	pt.		[PARIDE]
2857
			See Documentation/blockdev/paride.txt.
L
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2858

2859 2860 2861 2862
	pty.legacy_count=
			[KNL] Number of legacy pty's. Overwrites compiled-in
			default number.

2863
	quiet		[KNL] Disable most log messages
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2864

L
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2865 2866 2867 2868 2869
	r128=		[HW,DRM]

	raid=		[HW,RAID]
			See Documentation/md.txt.

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2870
	ramdisk_blocksize=	[RAM]
2871
			See Documentation/blockdev/ramdisk.txt.
R
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2872

L
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2873
	ramdisk_size=	[RAM] Sizes of RAM disks in kilobytes
2874
			See Documentation/blockdev/ramdisk.txt.
L
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2875

2876
	rcu_nocbs=	[KNL]
P
Paul E. McKenney 已提交
2877 2878 2879
			In kernels built with CONFIG_RCU_NOCB_CPU=y, set
			the specified list of CPUs to be no-callback CPUs.
			Invocation of these CPUs' RCU callbacks will
2880 2881 2882 2883
			be offloaded to "rcuox/N" kthreads created for
			that purpose, where "x" is "b" for RCU-bh, "p"
			for RCU-preempt, and "s" for RCU-sched, and "N"
			is the CPU number.  This reduces OS jitter on the
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Paul E. McKenney 已提交
2884 2885 2886 2887
			offloaded CPUs, which can be useful for HPC and
			real-time workloads.  It can also improve energy
			efficiency for asymmetric multiprocessors.

2888
	rcu_nocb_poll	[KNL]
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Paul E. McKenney 已提交
2889 2890 2891 2892 2893 2894 2895 2896 2897 2898
			Rather than requiring that offloaded CPUs
			(specified by rcu_nocbs= above) explicitly
			awaken the corresponding "rcuoN" kthreads,
			make these kthreads poll for callbacks.
			This improves the real-time response for the
			offloaded CPUs by relieving them of the need to
			wake up the corresponding kthread, but degrades
			energy efficiency by requiring that the kthreads
			periodically wake up to do the polling.

2899
	rcutree.blimit=	[KNL]
2900 2901
			Set maximum number of finished RCU callbacks to
			process in one batch.
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Dipankar Sarma 已提交
2902

2903
	rcutree.rcu_fanout_leaf= [KNL]
2904 2905 2906 2907
			Increase the number of CPUs assigned to each
			leaf rcu_node structure.  Useful for very large
			systems.

2908 2909 2910 2911 2912 2913
	rcutree.jiffies_till_sched_qs= [KNL]
			Set required age in jiffies for a
			given grace period before RCU starts
			soliciting quiescent-state help from
			rcu_note_context_switch().

2914
	rcutree.jiffies_till_first_fqs= [KNL]
2915 2916 2917 2918 2919
			Set delay from grace-period initialization to
			first attempt to force quiescent states.
			Units are jiffies, minimum value is zero,
			and maximum value is HZ.

2920
	rcutree.jiffies_till_next_fqs= [KNL]
2921 2922 2923 2924
			Set delay between subsequent attempts to force
			quiescent states.  Units are jiffies, minimum
			value is one, and maximum value is HZ.

2925 2926 2927 2928 2929 2930 2931
	rcutree.rcu_nocb_leader_stride= [KNL]
			Set the number of NOCB kthread groups, which
			defaults to the square root of the number of
			CPUs.  Larger numbers reduces the wakeup overhead
			on the per-CPU grace-period kthreads, but increases
			that same overhead on each group's leader.

2932
	rcutree.qhimark= [KNL]
2933 2934
			Set threshold of queued RCU callbacks beyond which
			batch limiting is disabled.
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Dipankar Sarma 已提交
2935

2936
	rcutree.qlowmark= [KNL]
2937 2938
			Set threshold of queued RCU callbacks below which
			batch limiting is re-enabled.
D
Dipankar Sarma 已提交
2939

2940
	rcutree.rcu_idle_gp_delay= [KNL]
2941 2942
			Set wakeup interval for idle CPUs that have
			RCU callbacks (RCU_FAST_NO_HZ=y).
2943

2944
	rcutree.rcu_idle_lazy_gp_delay= [KNL]
2945 2946 2947 2948
			Set wakeup interval for idle CPUs that have
			only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
			Lazy RCU callbacks are those which RCU can
			prove do nothing more than free memory.
2949

2950 2951 2952 2953 2954 2955 2956 2957 2958 2959 2960 2961 2962 2963 2964 2965 2966 2967
	rcutorture.cbflood_inter_holdoff= [KNL]
			Set holdoff time (jiffies) between successive
			callback-flood tests.

	rcutorture.cbflood_intra_holdoff= [KNL]
			Set holdoff time (jiffies) between successive
			bursts of callbacks within a given callback-flood
			test.

	rcutorture.cbflood_n_burst= [KNL]
			Set the number of bursts making up a given
			callback-flood test.  Set this to zero to
			disable callback-flood testing.

	rcutorture.cbflood_n_per_burst= [KNL]
			Set the number of callbacks to be registered
			in a given burst of a callback-flood test.

2968
	rcutorture.fqs_duration= [KNL]
2969 2970
			Set duration of force_quiescent_state bursts.

2971
	rcutorture.fqs_holdoff= [KNL]
2972 2973
			Set holdoff time within force_quiescent_state bursts.

2974
	rcutorture.fqs_stutter= [KNL]
2975 2976
			Set wait time between force_quiescent_state bursts.

2977 2978 2979 2980 2981 2982 2983 2984
	rcutorture.gp_exp= [KNL]
			Use expedited update-side primitives.

	rcutorture.gp_normal= [KNL]
			Use normal (non-expedited) update-side primitives.
			If both gp_exp and gp_normal are set, do both.
			If neither gp_exp nor gp_normal are set, still
			do both.
2985

2986
	rcutorture.n_barrier_cbs= [KNL]
2987 2988
			Set callbacks/threads for rcu_barrier() testing.

2989
	rcutorture.nfakewriters= [KNL]
2990 2991 2992 2993
			Set number of concurrent RCU writers.  These just
			stress RCU, they don't participate in the actual
			test, hence the "fake".

2994
	rcutorture.nreaders= [KNL]
2995 2996
			Set number of RCU readers.

2997 2998 2999 3000
	rcutorture.object_debug= [KNL]
			Enable debug-object double-call_rcu() testing.

	rcutorture.onoff_holdoff= [KNL]
3001 3002
			Set time (s) after boot for CPU-hotplug testing.

3003
	rcutorture.onoff_interval= [KNL]
3004 3005 3006
			Set time (s) between CPU-hotplug operations, or
			zero to disable CPU-hotplug testing.

3007
	rcutorture.torture_runnable= [BOOT]
3008 3009 3010
			Start rcutorture running at boot time.

	rcutorture.shuffle_interval= [KNL]
3011 3012 3013 3014
			Set task-shuffle interval (s).  Shuffling tasks
			allows some CPUs to go into dyntick-idle mode
			during the rcutorture test.

3015
	rcutorture.shutdown_secs= [KNL]
3016 3017 3018
			Set time (s) after boot system shutdown.  This
			is useful for hands-off automated testing.

3019
	rcutorture.stall_cpu= [KNL]
3020 3021 3022
			Duration of CPU stall (s) to test RCU CPU stall
			warnings, zero to disable.

3023
	rcutorture.stall_cpu_holdoff= [KNL]
3024 3025
			Time to wait (s) after boot before inducing stall.

3026
	rcutorture.stat_interval= [KNL]
3027 3028
			Time (s) between statistics printk()s.

3029
	rcutorture.stutter= [KNL]
3030 3031 3032 3033 3034
			Time (s) to stutter testing, for example, specifying
			five seconds causes the test to run for five seconds,
			wait for five seconds, and so on.  This tests RCU's
			ability to transition abruptly to and from idle.

3035
	rcutorture.test_boost= [KNL]
3036 3037 3038 3039
			Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
			"Maybe" means test if the RCU implementation
			under test support RCU priority boosting.

3040
	rcutorture.test_boost_duration= [KNL]
3041 3042
			Duration (s) of each individual boost test.

3043
	rcutorture.test_boost_interval= [KNL]
3044 3045
			Interval (s) between each boost test.

3046
	rcutorture.test_no_idle_hz= [KNL]
3047 3048 3049
			Test RCU's dyntick-idle handling.  See also the
			rcutorture.shuffle_interval parameter.

3050
	rcutorture.torture_type= [KNL]
3051 3052
			Specify the RCU implementation to test.

3053
	rcutorture.verbose= [KNL]
3054 3055
			Enable additional printk() statements.

3056 3057 3058 3059 3060 3061 3062 3063 3064 3065 3066 3067 3068
	rcupdate.rcu_expedited= [KNL]
			Use expedited grace-period primitives, for
			example, synchronize_rcu_expedited() instead
			of synchronize_rcu().  This reduces latency,
			but can increase CPU utilization, degrade
			real-time latency, and degrade energy efficiency.

	rcupdate.rcu_cpu_stall_suppress= [KNL]
			Suppress RCU CPU stall warning messages.

	rcupdate.rcu_cpu_stall_timeout= [KNL]
			Set timeout for RCU CPU stall warning messages.

3069 3070 3071 3072 3073
	rcupdate.rcu_task_stall_timeout= [KNL]
			Set timeout in jiffies for RCU task stall warning
			messages.  Disable with a value less than or equal
			to zero.

3074 3075 3076 3077 3078
	rdinit=		[KNL]
			Format: <full_path>
			Run specified binary instead of /init from the ramdisk,
			used for early userspace startup. See initrd.

3079 3080 3081 3082 3083 3084 3085 3086 3087 3088 3089
	reboot=		[KNL]
			Format (x86 or x86_64):
				[w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
				[[,]s[mp]#### \
				[[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
				[[,]f[orce]
			Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
			      reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
			      reboot_force is either force or not specified,
			      reboot_cpu is s[mp]#### with #### being the processor
					to be used for rebooting.
L
Linus Torvalds 已提交
3090

3091 3092
	relax_domain_level=
			[KNL, SMP] Set scheduler's default relax_domain_level.
3093
			See Documentation/cgroups/cpusets.txt.
3094

3095 3096 3097 3098 3099 3100 3101
	relative_sleep_states=
			[SUSPEND] Use sleep state labeling where the deepest
			state available other than hibernation is always "mem".
			Format: { "0" | "1" }
			0 -- Traditional sleep state labels.
			1 -- Relative sleep state labels.

L
Linus Torvalds 已提交
3102 3103
	reserve=	[KNL,BUGS] Force the kernel to ignore some iomem area

3104
	reservetop=	[X86-32]
3105 3106 3107 3108
			Format: nn[KMG]
			Reserves a hole at the top of the kernel virtual
			address space.

3109 3110 3111 3112 3113
	reservelow=	[X86]
			Format: nn[K]
			Set the amount of memory to reserve for BIOS at
			the bottom of the address space.

3114 3115 3116
	reset_devices	[KNL] Force drivers to reset the underlying device
			during initialization.

R
Randy Dunlap 已提交
3117 3118
	resume=		[SWSUSP]
			Specify the partition device for software suspend
3119 3120
			Format:
			{/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
L
Linus Torvalds 已提交
3121

3122 3123 3124 3125 3126 3127
	resume_offset=	[SWSUSP]
			Specify the offset from the beginning of the partition
			given by "resume=" at which the swap header is located,
			in <PAGE_SIZE> units (needed only for swap files).
			See  Documentation/power/swsusp-and-swap-files.txt

3128 3129 3130
	resumedelay=	[HIBERNATION] Delay (in seconds) to pause before attempting to
			read the resume files

3131 3132 3133 3134
	resumewait	[HIBERNATION] Wait (indefinitely) for resume device to show up.
			Useful for devices that are detected asynchronously
			(e.g. USB and MMC devices).

3135 3136 3137 3138
	hibernate=	[HIBERNATION]
		noresume	Don't check if there's a hibernation image
				present during boot.
		nocompress	Don't compress/decompress hibernation images.
3139
		no		Disable hibernation and resume.
3140

3141 3142
	retain_initrd	[RAM] Keep initrd memory after extraction

L
Linus Torvalds 已提交
3143 3144 3145 3146 3147 3148
	rhash_entries=	[KNL,NET]
			Set number of hash buckets for route cache

	ro		[KNL] Mount root device read-only on boot

	root=		[KNL] Root filesystem
3149
			See name_to_dev_t comment in init/do_mounts.c.
L
Linus Torvalds 已提交
3150 3151 3152 3153 3154 3155 3156 3157

	rootdelay=	[KNL] Delay (in seconds) to pause before attempting to
			mount the root filesystem

	rootflags=	[KNL] Set root filesystem mount option string

	rootfstype=	[KNL] Set root filesystem type

3158 3159 3160 3161
	rootwait	[KNL] Wait (indefinitely) for root device to show up.
			Useful for devices that are detected asynchronously
			(e.g. USB and MMC devices).

3162 3163 3164 3165 3166
	rproc_mem=nn[KMG][@address]
			[KNL,ARM,CMA] Remoteproc physical memory block.
			Memory area to be used by remote processor image,
			managed by CMA.

L
Linus Torvalds 已提交
3167 3168 3169 3170
	rw		[KNL] Mount root device read-write on boot

	S		[KNL] Run init in single mode

3171 3172 3173 3174 3175 3176 3177
	s390_iommu=	[HW,S390]
			Set s390 IOTLB flushing mode
		strict
			With strict flushing every unmap operation will result in
			an IOTLB flush. Default is lazy flushing before reuse,
			which is faster.

L
Linus Torvalds 已提交
3178 3179 3180 3181
	sa1100ir	[NET]
			See drivers/net/irda/sa1100_ir.c.

	sbni=		[NET] Granch SBNI12 leased line adapter
R
Randy Dunlap 已提交
3182

3183 3184
	sched_debug	[KNL] Enables verbose scheduler debug messages.

M
Mike Galbraith 已提交
3185 3186 3187 3188 3189 3190 3191 3192 3193
	skew_tick=	[KNL] Offset the periodic timer tick per cpu to mitigate
			xtime_lock contention on larger systems, and/or RCU lock
			contention on all systems with CONFIG_MAXSMP set.
			Format: { "0" | "1" }
			0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
			1 -- enable.
			Note: increases power consumption, thus should only be
			enabled if running jitter sensitive (HPC/RT) workloads.

3194 3195 3196 3197 3198 3199 3200
	security=	[SECURITY] Choose a security module to enable at boot.
			If this boot parameter is not specified, only the first
			security module asking for security registration will be
			loaded. An invalid security module name will be treated
			as if no module has been chosen.

	selinux=	[SELINUX] Disable or enable SELinux at boot time.
L
Linus Torvalds 已提交
3201 3202 3203 3204 3205 3206 3207 3208
			Format: { "0" | "1" }
			See security/selinux/Kconfig help text.
			0 -- disable.
			1 -- enable.
			Default value is set via kernel config option.
			If enabled at boot time, /selinux/disable can be used
			later to disable prior to initial policy load.

3209 3210 3211 3212 3213 3214 3215
	apparmor=	[APPARMOR] Disable or enable AppArmor at boot time
			Format: { "0" | "1" }
			See security/apparmor/Kconfig help text
			0 -- disable.
			1 -- enable.
			Default value is set via kernel config option.

3216
	serialnumber	[BUGS=X86-32]
L
Linus Torvalds 已提交
3217 3218 3219

	shapers=	[NET]
			Maximal number of shapers.
R
Randy Dunlap 已提交
3220

Y
Yinghai Lu 已提交
3221 3222 3223 3224 3225 3226
	show_msr=	[x86] show boot-time MSR settings
			Format: { <integer> }
			Show boot-time (BIOS-initialized) MSR settings.
			The parameter means the number of CPUs to show,
			for example 1 means boot CPU only.

L
Linus Torvalds 已提交
3227 3228
	simeth=		[IA-64]
	simscsi=
R
Randy Dunlap 已提交
3229

L
Linus Torvalds 已提交
3230 3231
	slram=		[HW,MTD]

3232 3233 3234 3235 3236 3237 3238
	slab_nomerge	[MM]
			Disable merging of slabs with similar size. May be
			necessary if there is some reason to distinguish
			allocs to different slabs. Debug options disable
			merging on their own.
			For more information see Documentation/vm/slub.txt.

3239 3240 3241 3242 3243 3244
	slab_max_order=	[MM, SLAB]
			Determines the maximum allowed order for slabs.
			A high setting may cause OOMs due to memory
			fragmentation.  Defaults to 1 for systems with
			more than 32MB of RAM, 0 otherwise.

3245 3246 3247 3248 3249 3250 3251
	slub_debug[=options[,slabs]]	[MM, SLUB]
			Enabling slub_debug allows one to determine the
			culprit if slab objects become corrupted. Enabling
			slub_debug can create guard zones around objects and
			may poison objects when not in use. Also tracks the
			last alloc / free. For more information see
			Documentation/vm/slub.txt.
C
Christoph Lameter 已提交
3252 3253

	slub_max_order= [MM, SLUB]
3254 3255 3256 3257
			Determines the maximum allowed order for slabs.
			A high setting may cause OOMs due to memory
			fragmentation. For more information see
			Documentation/vm/slub.txt.
C
Christoph Lameter 已提交
3258 3259

	slub_min_objects=	[MM, SLUB]
3260 3261 3262 3263 3264 3265
			The minimum number of objects per slab. SLUB will
			increase the slab order up to slub_max_order to
			generate a sufficiently large slab able to contain
			the number of objects indicated. The higher the number
			of objects the smaller the overhead of tracking slabs
			and the less frequently locks need to be acquired.
C
Christoph Lameter 已提交
3266 3267 3268
			For more information see Documentation/vm/slub.txt.

	slub_min_order=	[MM, SLUB]
3269
			Determines the minimum page order for slabs. Must be
3270
			lower than slub_max_order.
C
Christoph Lameter 已提交
3271 3272 3273
			For more information see Documentation/vm/slub.txt.

	slub_nomerge	[MM, SLUB]
3274 3275
			Same with slab_nomerge. This is supported for legacy.
			See slab_nomerge for more information.
C
Christoph Lameter 已提交
3276

L
Linus Torvalds 已提交
3277 3278 3279
	smart2=		[HW]
			Format: <io1>[,<io2>[,...,<io8>]]

B
Bjorn Helgaas 已提交
3280 3281 3282 3283 3284 3285 3286 3287 3288 3289 3290
	smsc-ircc2.nopnp	[HW] Don't use PNP to discover SMC devices
	smsc-ircc2.ircc_cfg=	[HW] Device configuration I/O port
	smsc-ircc2.ircc_sir=	[HW] SIR base I/O port
	smsc-ircc2.ircc_fir=	[HW] FIR base I/O port
	smsc-ircc2.ircc_irq=	[HW] IRQ line
	smsc-ircc2.ircc_dma=	[HW] DMA channel
	smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
				0: Toshiba Satellite 1800 (GP data pin select)
				1: Fast pin select (default)
				2: ATC IRMode

I
Ingo Molnar 已提交
3291 3292
	softlockup_panic=
			[KNL] Should the soft-lockup detector generate panics.
3293
			Format: <integer>
I
Ingo Molnar 已提交
3294

3295 3296 3297 3298 3299
	softlockup_all_cpu_backtrace=
			[KNL] Should the soft-lockup detector generate
			backtraces on all cpus.
			Format: <integer>

L
Linus Torvalds 已提交
3300
	sonypi.*=	[HW] Sony Programmable I/O Control Device driver
P
Paul Bolle 已提交
3301
			See Documentation/laptops/sonypi.txt
L
Linus Torvalds 已提交
3302 3303 3304 3305 3306 3307

	spia_io_base=	[HW,MTD]
	spia_fio_base=
	spia_pedr=
	spia_peddr=

3308 3309 3310
	stacktrace	[FTRACE]
			Enabled the stack tracer on boot up.

3311 3312 3313 3314 3315 3316 3317 3318
	stacktrace_filter=[function-list]
			[FTRACE] Limit the functions that the stack tracer
			will trace at boot up. function-list is a comma separated
			list of functions. This list can be changed at run
			time by the stack_trace_filter file in the debugfs
			tracing directory. Note, this enables stack tracing
			and the stacktrace above is not needed.

L
Linus Torvalds 已提交
3319 3320 3321 3322 3323 3324 3325 3326 3327 3328 3329 3330 3331
	sti=		[PARISC,HW]
			Format: <num>
			Set the STI (builtin display/keyboard on the HP-PARISC
			machines) console (graphic card) which should be used
			as the initial boot-console.
			See also comment in drivers/video/console/sticore.c.

	sti_font=	[HW]
			See comment in drivers/video/console/sticore.c.

	stifb=		[HW]
			Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]

3332 3333 3334 3335 3336 3337 3338 3339 3340 3341 3342 3343
	sunrpc.min_resvport=
	sunrpc.max_resvport=
			[NFS,SUNRPC]
			SunRPC servers often require that client requests
			originate from a privileged port (i.e. a port in the
			range 0 < portnr < 1024).
			An administrator who wishes to reserve some of these
			ports for other uses may adjust the range that the
			kernel's sunrpc client considers to be privileged
			using these two parameters to set the minimum and
			maximum port values.

3344 3345 3346 3347 3348 3349 3350 3351 3352 3353 3354 3355 3356 3357 3358 3359
	sunrpc.pool_mode=
			[NFS]
			Control how the NFS server code allocates CPUs to
			service thread pools.  Depending on how many NICs
			you have and where their interrupts are bound, this
			option will affect which CPUs will do NFS serving.
			Note: this parameter cannot be changed while the
			NFS server is running.

			auto	    the server chooses an appropriate mode
				    automatically using heuristics
			global	    a single global pool contains all CPUs
			percpu	    one pool for each CPU
			pernode	    one pool for each NUMA node (equivalent
				    to global on non-NUMA machines)

3360 3361 3362 3363 3364 3365 3366 3367 3368
	sunrpc.tcp_slot_table_entries=
	sunrpc.udp_slot_table_entries=
			[NFS,SUNRPC]
			Sets the upper limit on the number of simultaneous
			RPC calls that can be sent from the client to a
			server. Increasing these values may allow you to
			improve throughput, but will also increase the
			amount of memory reserved for use by the client.

3369
	swapaccount=[0|1]
3370 3371 3372 3373
			[KNL] Enable accounting of swap in memory resource
			controller if no parameter or 1 is given or disable
			it if 0 is given (See Documentation/cgroups/memory.txt)

J
Jiri Kosina 已提交
3374 3375 3376 3377 3378
	swiotlb=	[ARM,IA-64,PPC,MIPS,X86]
			Format: { <int> | force }
			<int> -- Number of I/O TLB slabs
			force -- force using of bounce buffers even if they
			         wouldn't be automatically used by the kernel
R
Randy Dunlap 已提交
3379

L
Linus Torvalds 已提交
3380 3381
	switches=	[HW,M68k]

3382 3383 3384 3385 3386 3387 3388 3389 3390
	sysfs.deprecated=0|1 [KNL]
			Enable/disable old style sysfs layout for old udev
			on older distributions. When this option is enabled
			very new udev will not work anymore. When this option
			is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
			in older udev will not work anymore.
			Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
			the kernel configuration.

3391 3392 3393 3394 3395 3396
	sysrq_always_enabled
			[KNL]
			Ignore sysrq setting - this boot parameter will
			neutralize any effect of /proc/sys/kernel/sysrq.
			Useful for debugging.

L
Linus Torvalds 已提交
3397 3398
	tdfx=		[HW,DRM]

3399
	test_suspend=	[SUSPEND][,N]
D
David Brownell 已提交
3400
			Specify "mem" (for Suspend-to-RAM) or "standby" (for
3401 3402 3403 3404 3405
			standby suspend) or "freeze" (for suspend type freeze)
			as the system sleep state during system startup with
			the optional capability to repeat N number of times.
			The system is woken from this state using a
			wakeup-capable RTC alarm.
D
David Brownell 已提交
3406

L
Linus Torvalds 已提交
3407 3408 3409
	thash_entries=	[KNL,NET]
			Set number of hash buckets for TCP connection

3410 3411 3412 3413
	thermal.act=	[HW,ACPI]
			-1: disable all active trip points in all thermal zones
			<degrees C>: override all lowest active trip points

3414 3415
	thermal.crt=	[HW,ACPI]
			-1: disable all critical trip points in all thermal zones
3416
			<degrees C>: override all critical trip points
3417

3418 3419 3420 3421
	thermal.nocrt=	[HW,ACPI]
			Set to disable actions on ACPI thermal zone
			critical and hot trip points.

3422 3423 3424
	thermal.off=	[HW,ACPI]
			1: disable ACPI thermal control

3425 3426
	thermal.psv=	[HW,ACPI]
			-1: disable all passive trip points
3427 3428
			<degrees C>: override all passive trip points to this
			value
3429

3430 3431 3432 3433 3434
	thermal.tzp=	[HW,ACPI]
			Specify global default ACPI thermal zone polling rate
			<deci-seconds>: poll all this frequency
			0: no polling (default)

3435 3436
	threadirqs	[KNL]
			Force threading of all interrupt handlers except those
3437
			marked explicitly IRQF_NO_THREAD.
3438

3439 3440 3441 3442 3443 3444 3445 3446 3447
	tmem		[KNL,XEN]
			Enable the Transcendent memory driver if built-in.

	tmem.cleancache=0|1 [KNL, XEN]
			Default is on (1). Disable the usage of the cleancache
			API to send anonymous pages to the hypervisor.

	tmem.frontswap=0|1 [KNL, XEN]
			Default is on (1). Disable the usage of the frontswap
3448 3449
			API to send swap pages to the hypervisor. If disabled
			the selfballooning and selfshrinking are force disabled.
3450 3451 3452 3453 3454 3455 3456 3457 3458 3459

	tmem.selfballooning=0|1 [KNL, XEN]
			Default is on (1). Disable the driving of swap pages
			to the hypervisor.

	tmem.selfshrinking=0|1 [KNL, XEN]
			Default is on (1). Partial swapoff that immediately
			transfers pages from Xen hypervisor back to the
			kernel based on different criteria.

3460 3461 3462
	topology=	[S390]
			Format: {off | on}
			Specify if the kernel should make use of the cpu
3463 3464
			topology information if the hardware supports this.
			The scheduler will make use of this information and
3465
			e.g. base its process migration decisions on it.
H
Heiko Carstens 已提交
3466
			Default is on.
3467

L
Linus Torvalds 已提交
3468 3469
	tp720=		[HW,PS2]

3470 3471 3472 3473 3474 3475 3476 3477 3478
	tpm_suspend_pcr=[HW,TPM]
			Format: integer pcr id
			Specify that at suspend time, the tpm driver
			should extend the specified pcr with zeros,
			as a workaround for some chips which fail to
			flush the last written pcr on TPM_SaveState.
			This will guarantee that all the other pcrs
			are saved.

3479 3480
	trace_buf_size=nn[KMG]
			[FTRACE] will set tracing buffer size.
3481

3482 3483 3484 3485 3486
	trace_event=[event-list]
			[FTRACE] Set and start specified trace events in order
			to facilitate early boot debugging.
			See also Documentation/trace/events.txt

3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502
	trace_options=[option-list]
			[FTRACE] Enable or disable tracer options at boot.
			The option-list is a comma delimited list of options
			that can be enabled or disabled just as if you were
			to echo the option name into

			    /sys/kernel/debug/tracing/trace_options

			For example, to enable stacktrace option (to dump the
			stack trace of each event), add to the command line:

			      trace_options=stacktrace

			See also Documentation/trace/ftrace.txt "trace options"
			section.

3503 3504 3505 3506 3507 3508 3509 3510 3511 3512 3513 3514 3515
	traceoff_on_warning
			[FTRACE] enable this option to disable tracing when a
			warning is hit. This turns off "tracing_on". Tracing can
			be enabled again by echoing '1' into the "tracing_on"
			file located in /sys/kernel/debug/tracing/

			This option is useful, as it disables the trace before
			the WARNING dump is called, which prevents the trace to
			be filled with content caused by the warning output.

			This option can also be set at run time via the sysctl
			option:  kernel/traceoff_on_warning

3516 3517 3518 3519 3520 3521 3522
	transparent_hugepage=
			[KNL]
			Format: [always|madvise|never]
			Can be used to control the default behavior of the system
			with respect to transparent hugepages.
			See Documentation/vm/transhuge.txt for more details.

3523
	tsc=		Disable clocksource stability checks for TSC.
3524 3525
			Format: <string>
			[x86] reliable: mark tsc clocksource as reliable, this
3526 3527 3528 3529
			disables clocksource verification at runtime, as well
			as the stability checks done at bootup.	Used to enable
			high-resolution timer mode on older hardware, and in
			virtualized environment.
V
Venkatesh Pallipadi 已提交
3530 3531 3532 3533
			[x86] noirqtime: Do not use TSC to do irq accounting.
			Used to run time disable IRQ_TIME_ACCOUNTING on any
			platforms where RDTSC is slow and this accounting
			can add overhead.
3534

R
Randy Dunlap 已提交
3535 3536 3537 3538
	turbografx.map[2|3]=	[HW,JOY]
			TurboGraFX parallel port interface
			Format:
			<port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
L
Linus Torvalds 已提交
3539 3540
			See also Documentation/input/joystick-parport.txt

C
Christian Kujau 已提交
3541 3542 3543 3544 3545
	udbg-immortal	[PPC] When debugging early kernel crashes that
			happen after console_init() and before a proper 
			console driver takes over, this boot options might
			help "seeing" what's going on.

3546 3547 3548
	uhash_entries=	[KNL,NET]
			Set number of hash buckets for UDP/UDP-Lite connections

3549 3550 3551 3552 3553 3554 3555 3556
	uhci-hcd.ignore_oc=
			[USB] Ignore overcurrent events (default N).
			Some badly-designed motherboards generate lots of
			bogus events, for ports that aren't wired to
			anything.  Set this parameter to avoid log spamming.
			Note that genuine overcurrent events won't be
			reported either.

3557
	unknown_nmi_panic
3558
			[X86] Cause panic on unknown NMI.
3559

3560 3561 3562 3563 3564
	usbcore.authorized_default=
			[USB] Default USB device authorization:
			(default -1 = authorized except for wireless USB,
			0 = not authorized, 1 = authorized)

3565 3566 3567 3568 3569
	usbcore.autosuspend=
			[USB] The autosuspend time delay (in seconds) used
			for newly-detected USB devices (default 2).  This
			is the time required before an idle device will be
			autosuspended.  Devices for which the delay is set
3570
			to a negative value won't be autosuspended at all.
3571

3572 3573 3574 3575 3576 3577 3578 3579 3580 3581
	usbcore.usbfs_snoop=
			[USB] Set to log all usbfs traffic (default 0 = off).

	usbcore.blinkenlights=
			[USB] Set to cycle leds on hubs (default 0 = off).

	usbcore.old_scheme_first=
			[USB] Start with the old device initialization
			scheme (default 0 = off).

3582 3583 3584 3585
	usbcore.usbfs_memory_mb=
			[USB] Memory limit (in MB) for buffers allocated by
			usbfs (default = 16, 0 = max = 2047).

3586 3587 3588 3589 3590 3591 3592 3593 3594
	usbcore.use_both_schemes=
			[USB] Try the other device initialization scheme
			if the first one fails (default 1 = enabled).

	usbcore.initial_descriptor_timeout=
			[USB] Specifies timeout for the initial 64-byte
                        USB_REQ_GET_DESCRIPTOR request in milliseconds
			(default 5000 = 5.0 seconds).

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Linus Torvalds 已提交
3595 3596
	usbhid.mousepoll=
			[USBHID] The interval which mice are to be polled at.
R
Randy Dunlap 已提交
3597

3598 3599 3600 3601 3602 3603 3604 3605 3606 3607 3608 3609
	usb-storage.delay_use=
			[UMS] The delay in seconds before a new device is
			scanned for Logical Units (default 5).

	usb-storage.quirks=
			[UMS] A list of quirks entries to supplement or
			override the built-in unusual_devs list.  List
			entries are separated by commas.  Each entry has
			the form VID:PID:Flags where VID and PID are Vendor
			and Product ID values (4-digit hex numbers) and
			Flags is a set of characters, each corresponding
			to a common usb-storage quirk flag as follows:
3610 3611
				a = SANE_SENSE (collect more than 18 bytes
					of sense data);
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Alan Stern 已提交
3612 3613
				b = BAD_SENSE (don't collect more than 18
					bytes of sense data);
3614 3615
				c = FIX_CAPACITY (decrease the reported
					device capacity by one sector);
3616 3617 3618 3619
				d = NO_READ_DISC_INFO (don't use
					READ_DISC_INFO command);
				e = NO_READ_CAPACITY_16 (don't use
					READ_CAPACITY_16 command);
H
Hans de Goede 已提交
3620 3621
				f = NO_REPORT_OPCODES (don't use report opcodes
					command, uas only);
3622 3623 3624
				h = CAPACITY_HEURISTICS (decrease the
					reported device capacity by one
					sector if the number is odd);
3625 3626 3627 3628 3629 3630
				i = IGNORE_DEVICE (don't bind to this
					device);
				l = NOT_LOCKABLE (don't try to lock and
					unlock ejectable media);
				m = MAX_SECTORS_64 (don't transfer more
					than 64 sectors = 32 KB at a time);
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Alan Stern 已提交
3631 3632
				n = INITIAL_READ10 (force a retry of the
					initial READ(10) command);
3633 3634
				o = CAPACITY_OK (accept the capacity
					reported by the device);
3635 3636
				p = WRITE_CACHE (the device cache is ON
					by default);
3637 3638 3639 3640
				r = IGNORE_RESIDUE (the device reports
					bogus residue values);
				s = SINGLE_LUN (the device has only one
					Logical Unit);
3641 3642
				t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
					commands, uas only);
3643
				u = IGNORE_UAS (don't bind to the uas driver);
3644 3645 3646 3647
				w = NO_WP_DETECT (don't test whether the
					medium is write-protected).
			Example: quirks=0419:aaf5:rl,0421:0433:rc

3648 3649 3650 3651 3652 3653 3654 3655 3656 3657
	user_debug=	[KNL,ARM]
			Format: <int>
			See arch/arm/Kconfig.debug help text.
				 1 - undefined instruction events
				 2 - system calls
				 4 - invalid data aborts
				 8 - SIGSEGV faults
				16 - SIGBUS faults
			Example: user_debug=31

3658 3659 3660 3661 3662 3663 3664
	userpte=
			[X86] Flags controlling user PTE allocations.

				nohigh = do not allocate PTE pages in
					HIGHMEM regardless of setting
					of CONFIG_HIGHPTE.

3665
	vdso=		[X86,SH]
3666 3667 3668
			On X86_32, this is an alias for vdso32=.  Otherwise:

			vdso=1: enable VDSO (the default)
3669 3670
			vdso=0: disable VDSO mapping

3671 3672 3673 3674 3675 3676 3677 3678 3679 3680 3681 3682 3683
	vdso32=		[X86] Control the 32-bit vDSO
			vdso32=1: enable 32-bit VDSO
			vdso32=0 or vdso32=2: disable 32-bit VDSO

			See the help text for CONFIG_COMPAT_VDSO for more
			details.  If CONFIG_COMPAT_VDSO is set, the default is
			vdso32=0; otherwise, the default is vdso32=1.

			For compatibility with older kernels, vdso32=2 is an
			alias for vdso32=0.

			Try vdso32=0 if you encounter an error that says:
			dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
R
Roland McGrath 已提交
3684

3685 3686 3687
	vector=		[IA-64,SMP]
			vector=percpu: enable percpu vector domain

L
Linus Torvalds 已提交
3688 3689 3690
	video=		[FB] Frame buffer configuration
			See Documentation/fb/modedb.txt.

3691 3692 3693 3694 3695 3696 3697
	video.brightness_switch_enabled= [0,1]
			If set to 1, on receiving an ACPI notify event
			generated by hotkey, video driver will adjust brightness
			level and then send out the event to user space through
			the allocated input device; If set to 0, video driver
			will only send out the event without touching backlight
			brightness level.
3698
			default: 1
3699

3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711 3712 3713 3714 3715
	virtio_mmio.device=
			[VMMIO] Memory mapped virtio (platform) device.

				<size>@<baseaddr>:<irq>[:<id>]
			where:
				<size>     := size (can use standard suffixes
						like K, M and G)
				<baseaddr> := physical base address
				<irq>      := interrupt number (as passed to
						request_irq())
				<id>       := (optional) platform device id
			example:
				virtio_mmio.device=1K@0x100b0000:48:7

			Can be used multiple times for multiple devices.

3716
	vga=		[BOOT,X86-32] Select a particular video mode
3717
			See Documentation/x86/boot.txt and
R
Randy Dunlap 已提交
3718
			Documentation/svga.txt.
L
Linus Torvalds 已提交
3719 3720 3721 3722
			Use vga=ask for menu.
			This is actually a boot loader parameter; the value is
			passed to the kernel using a special protocol.

R
Randy Dunlap 已提交
3723
	vmalloc=nn[KMG]	[KNL,BOOT] Forces the vmalloc area to have an exact
L
Linus Torvalds 已提交
3724 3725 3726 3727 3728
			size of <nn>. This can be used to increase the
			minimum size (128MB on x86). It can also be used to
			decrease the size and leave more room for directly
			mapped kernel RAM.

3729 3730
	vmhalt=		[KNL,S390] Perform z/VM CP command after system halt.
			Format: <command>
L
Linus Torvalds 已提交
3731

3732 3733 3734 3735 3736
	vmpanic=	[KNL,S390] Perform z/VM CP command after kernel panic.
			Format: <command>

	vmpoff=		[KNL,S390] Perform z/VM CP command after power off.
			Format: <command>
R
Randy Dunlap 已提交
3737

3738 3739 3740 3741 3742 3743 3744 3745
	vsyscall=	[X86-64]
			Controls the behavior of vsyscalls (i.e. calls to
			fixed addresses of 0xffffffffff600x00 from legacy
			code).  Most statically-linked binaries and older
			versions of glibc use these calls.  Because these
			functions are at fixed addresses, they make nice
			targets for exploits that can control RIP.

A
Andy Lutomirski 已提交
3746 3747
			emulate     [default] Vsyscalls turn into traps and are
			            emulated reasonably safely.
3748

A
Andy Lutomirski 已提交
3749
			native      Vsyscalls are native syscall instructions.
3750 3751 3752 3753 3754 3755 3756 3757 3758
			            This is a little bit faster than trapping
			            and makes a few dynamic recompilers work
			            better than they would in emulation mode.
			            It also makes exploits much easier to write.

			none        Vsyscalls don't work at all.  This makes
			            them quite hard to use for exploits but
			            might break your system.

3759 3760 3761 3762
	vt.color=	[VT] Default text color.
			Format: 0xYX, X = foreground, Y = background.
			Default: 0x07 = light gray on black.

3763 3764 3765 3766 3767
	vt.cur_default=	[VT] Default cursor shape.
			Format: 0xCCBBAA, where AA, BB, and CC are the same as
			the parameters of the <Esc>[?A;B;Cc escape sequence;
			see VGA-softcursor.txt. Default: 2 = underline.

3768 3769 3770 3771 3772 3773 3774 3775 3776 3777 3778 3779 3780 3781 3782 3783 3784 3785 3786 3787 3788 3789 3790 3791 3792
	vt.default_blu=	[VT]
			Format: <blue0>,<blue1>,<blue2>,...,<blue15>
			Change the default blue palette of the console.
			This is a 16-member array composed of values
			ranging from 0-255.

	vt.default_grn=	[VT]
			Format: <green0>,<green1>,<green2>,...,<green15>
			Change the default green palette of the console.
			This is a 16-member array composed of values
			ranging from 0-255.

	vt.default_red=	[VT]
			Format: <red0>,<red1>,<red2>,...,<red15>
			Change the default red palette of the console.
			This is a 16-member array composed of values
			ranging from 0-255.

	vt.default_utf8=
			[VT]
			Format=<0|1>
			Set system-wide default UTF-8 mode for all tty's.
			Default is 1, i.e. UTF-8 mode is enabled for all
			newly opened terminals.

3793 3794 3795 3796 3797 3798 3799 3800 3801
	vt.global_cursor_default=
			[VT]
			Format=<-1|0|1>
			Set system-wide default for whether a cursor
			is shown on new VTs. Default is -1,
			i.e. cursors will be created by default unless
			overridden by individual drivers. 0 will hide
			cursors, 1 will display them.

3802 3803 3804 3805 3806 3807
	vt.italic=	[VT] Default color for italic text; 0-15.
			Default: 2 = green.

	vt.underline=	[VT] Default color for underlined text; 0-15.
			Default: 3 = cyan.

3808 3809 3810 3811
	watchdog timers	[HW,WDT] For information on watchdog timers,
			see Documentation/watchdog/watchdog-parameters.txt
			or other driver-specific files in the
			Documentation/watchdog/ directory.
L
Linus Torvalds 已提交
3812

3813 3814 3815 3816 3817 3818 3819 3820 3821
	workqueue.disable_numa
			By default, all work items queued to unbound
			workqueues are affine to the NUMA nodes they're
			issued on, which results in better behavior in
			general.  If NUMA affinity needs to be disabled for
			whatever reason, this option can be used.  Note
			that this also can be controlled per-workqueue for
			workqueues visible under /sys/bus/workqueue/.

3822 3823 3824 3825 3826 3827 3828 3829 3830 3831 3832 3833 3834 3835 3836
	workqueue.power_efficient
			Per-cpu workqueues are generally preferred because
			they show better performance thanks to cache
			locality; unfortunately, per-cpu workqueues tend to
			be more power hungry than unbound workqueues.

			Enabling this makes the per-cpu workqueues which
			were observed to contribute significantly to power
			consumption unbound, leading to measurably lower
			power usage at the cost of small performance
			overhead.

			The default value of this parameter is determined by
			the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.

3837 3838 3839 3840
	x2apic_phys	[X86-64,APIC] Use x2apic physical mode instead of
			default x2apic cluster mode on platforms
			supporting x2apic.

3841 3842
	x86_intel_mid_timer= [X86-32,APBT]
			Choose timer option for x86 Intel MID platform.
3843 3844
			Two valid options are apbt timer only and lapic timer
			plus one apbt timer for broadcast timer.
3845
			x86_intel_mid_timer=apbt_only | lapic_and_apbt
3846

3847 3848 3849 3850 3851 3852 3853
	xen_emul_unplug=		[HW,X86,XEN]
			Unplug Xen emulated devices
			Format: [unplug0,][unplug1]
			ide-disks -- unplug primary master IDE devices
			aux-ide-disks -- unplug non-primary-master IDE devices
			nics -- unplug network devices
			all -- unplug all emulated devices (NICs and IDE disks)
3854 3855 3856
			unnecessary -- unplugging emulated devices is
				unnecessary even if the host did not respond to
				the unplug protocol
3857
			never -- do not unplug even if version check succeeds
3858

3859 3860 3861 3862
	xen_nopvspin	[X86,XEN]
			Disables the ticketlock slowpath using Xen PV
			optimizations.

3863 3864 3865 3866
	xen_nopv	[X86]
			Disables the PV optimizations forcing the HVM guest to
			run as generic HVM guest with no PV drivers.

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Linus Torvalds 已提交
3867
	xirc2ps_cs=	[NET,PCMCIA]
R
Randy Dunlap 已提交
3868 3869
			Format:
			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
L
Linus Torvalds 已提交
3870

R
Randy Dunlap 已提交
3871
______________________________________________________________________
L
Linus Torvalds 已提交
3872 3873 3874 3875

TODO:

	Add more DRM drivers.