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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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cpu lists:
----------

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

	<cpu number>,...,<cpu number>

or

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

or a mixture

<cpu number>,...,<cpu number>-<cpu number>

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

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

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

	isolcpus=1,2,10-20,100-2000:2/25

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



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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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	X86_UV	SGI UV support is enabled.
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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,ARM64]
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			Advanced Configuration and Power Interface
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			Format: { force | on | off | strict | noirq | rsdt |
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				  copy_dsdt }
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			force -- enable ACPI if default was off
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			on -- enable ACPI but allow fallback to DT [arm64]
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			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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			For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
			are available
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			See also Documentation/power/runtime_pm.txt, pci=noacpi
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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_force_32bit_fadt_addr
			force FADT to use 32 bit addresses rather than the
			64 bit X_* addresses. Some firmware have broken 64
			bit addresses for force ACPI ignore these and use
			the older legacy 32 bit addresses.

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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.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_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_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_memhotplug [ACPI] Disable memory hotplug.  Useful for kdump
			   kernels.

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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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	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_os_name=	[HW,ACPI] Tell ACPI BIOS the name of the OS
			Format: To spoof as Windows 98: ="Microsoft Windows"

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	acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
			of 2 which is mandated by ACPI 6) as the supported ACPI
			specification revision (when using this switch, it may
			be necessary to carry out a cold reboot _twice_ in a
			row to make it take effect on the platform firmware).

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	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=!!		# enable 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

	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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	amd_iommu_intr=	[HW,X86-64]
			Specifies one of the following AMD IOMMU interrupt
			remapping modes:
			legacy     - Use legacy interrupt remapping mode.
			vapic      - Use virtual APIC mode, which allows IOMMU
			             to inject interrupts directly into guest.
			             This mode requires kvm-amd.avic=1.
			             (Default when IOMMU HW support is present.)

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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.

520
	apic=		[APIC,X86-32] Advanced Programmable Interrupt Controller
521
			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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	apic_extnmi=	[APIC,X86] External NMI delivery setting
			Format: { bsp (default) | all | none }
			bsp:  External NMI is delivered only to CPU 0
			all:  External NMIs are broadcast to all CPUs as a
			      backup of CPU 0
			none: External NMI is masked for all CPUs. This is
			      useful so that a dump capture kernel won't be
			      shot down by NMI

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

538 539 540 541 542 543 544 545 546
	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
548
			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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574 575
	audit=		[KNL] Enable the audit sub-system
			Format: { "0" | "1" } (0 = disabled, 1 = enabled)
576 577 578 579 580 581 582 583
			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.
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			Default: unset
585

586 587 588 589
	audit_backlog_limit= [KNL] Set the audit queue size limit.
			Format: <int> (must be >=0)
			Default: 64

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	bau=		[X86_UV] Enable the BAU on SGI UV.  The default
			behavior is to disable the BAU (i.e. bau=0).
			Format: { "0" | "1" }
			0 - Disable the BAU.
			1 - Enable the BAU.
			unset - Disable the BAU.

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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.

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	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

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	bootmem_debug	[KNL] Enable bootmem allocator debug messages.

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	bert_disable	[ACPI]
			Disable BERT OS support on buggy BIOSes.

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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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	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

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	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.

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	ca_keys=	[KEYS] This parameter identifies a specific key(s) on
			the system trusted keyring to be used for certificate
			trust validation.
650
			format: { id:<keyid> | builtin }
651

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	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).

658 659
	ccw_timeout_log [S390]
			See Documentation/s390/CommonIO for details.
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661 662
	cgroup_disable= [KNL] Disable a particular controller
			Format: {name of the controller(s) to disable}
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			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}
671

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	cgroup_no_v1=	[KNL] Disable one, multiple, all cgroup controllers in v1
			Format: { controller[,controller...] | "all" }
			Like cgroup_disable, but only applies to cgroup v1;
			the blacklisted controllers remain available in cgroup2.

677 678 679
	cgroup.memory=	[KNL] Pass options to the cgroup memory controller.
			Format: <string>
			nosocket -- Disable socket memory accounting.
680
			nokmem -- Disable kernel memory accounting.
681

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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.
694 695
	clk_ignore_unused
			[CLK]
696 697 698 699 700 701 702 703 704
			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.
705

706
	clock=		[BUGS=X86-32, HW] gettimeofday clocksource override.
707
			[Deprecated]
708
			Forces specified clocksource (if available) to be used
709
			when calculating gettimeofday(). If specified
710
			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
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			[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

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	clocksource.arm_arch_timer.evtstrm=
			[ARM,ARM64]
			Format: <bool>
			Enable/disable the eventstream feature of the ARM
			architected timer so that code using WFE-based polling
			loops can be debugged more effectively on production
			systems.

741 742 743 744 745 746 747 748 749
	clocksource.arm_arch_timer.fsl-a008585=
			[ARM64]
			Format: <bool>
			Enable/disable the workaround of Freescale/NXP
			erratum A-008585.  This can be useful for KVM
			guests, if the guest device tree doesn't show the
			erratum.  If unspecified, the workaround is
			enabled based on the device tree.

750 751
	clearcpuid=BITNUM [X86]
			Disable CPUID feature X for the kernel. See
752
			arch/x86/include/asm/cpufeatures.h for the valid bit
753
			numbers. Note the Linux specific bits are not necessarily
754 755 756 757 758 759 760 761 762
			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.

763 764 765 766 767
	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
770 771
			include/linux/dma-contiguous.h

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	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

779 780
	coherent_pool=nn[KMG]	[ARM,KNL]
			Sets the size of memory pool for coherent, atomic dma
781
			allocations, by default set to 256K.
782

783
	code_bytes	[X86] How many bytes of object code to print
784
			in an oops report.
785 786 787
			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]
807
		ttyUSB0[,options]
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			Use the specified serial port.  The options are of
809 810 811 812 813 814 815 816 817
			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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819 820
		uart[8250],io,<addr>[,options]
		uart[8250],mmio,<addr>[,options]
821
		uart[8250],mmio16,<addr>[,options]
822 823
		uart[8250],mmio32,<addr>[,options]
		uart[8250],0x<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,
826 827
			switching to the matching ttyS device later.
			MMIO inter-register address stride is either 8-bit
828 829 830 831
			(mmio), 16-bit (mmio16), or 32-bit (mmio32).
			If none of [io|mmio|mmio16|mmio32], <addr> is assumed
			to be equivalent to 'mmio'. 'options' are specified in
			the same format described for ttyS above; if unspecified,
832 833
			the h/w is not re-initialized.

834 835
		hvc<n>	Use the hypervisor console device <n>. This is for
			both Xen and PowerPC hypervisors.
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837 838 839 840 841
                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.

842 843 844 845
	consoleblank=	[KNL] The console blank (screen saver) timeout in
			seconds. Defaults to 10*60 = 10mins. A value of 0
			disables the blank timer.

846 847 848 849 850
	coredump_filter=
			[KNL] Change the default value for
			/proc/<pid>/coredump_filter.
			See also Documentation/filesystems/proc.txt.

851 852 853
	cpuidle.off=1	[CPU_IDLE]
			disable the cpuidle sub-system

854 855 856 857 858 859
	cpu_init_udelay=N
			[X86] Delay for N microsec between assert and de-assert
			of APIC INIT to start processors.  This delay occurs
			on every CPU online, such as boot, and resume from suspend.
			Default: 10000

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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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864 865 866 867 868 869 870
	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.
871

872 873 874 875 876
	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
877
			Documentation/kdump/kdump.txt for an example.
878

879
	crashkernel=size[KMG],high
880 881 882 883 884 885
			[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.
886 887 888
	crashkernel=size[KMG],low
			[KNL, x86_64] range under 4G. When crashkernel=X,high
			is passed, kernel could allocate physical memory region
889 890
			above 4G, that cause second kernel crash on system
			that require some amount of low memory, e.g. swiotlb
891 892 893 894
			requires at least 64M+32K low memory, also enough extra
			low memory is needed to make sure DMA buffers for 32-bit
			devices won't run out. Kernel would try to allocate at
			at least 256M below 4G automatically.
895 896 897
			This one let user to specify own low range under 4G
			for second kernel instead.
			0: to disable low allocation.
898
			It will be ignored when crashkernel=X,high is not used
899
			or memory reserved is below 4G.
900

901 902 903
	cryptomgr.notests
                        [KNL] Disable crypto self-tests

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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

918 919
	ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
			time. See Documentation/dynamic-debug-howto.txt for
920
			details.  Deprecated, see dyndbg.
921

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

924 925 926 927 928 929 930 931 932
	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.

933 934
	debug_objects	[KNL] Enable object debugging

935 936 937
	no_debug_objects
			[KNL] Disable object debugging

938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956
	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.

957 958 959 960 961 962 963 964 965
	debug_pagealloc=
			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
			parameter enables the feature at boot time. In
			default, it is disabled. We can avoid allocating huge
			chunk of memory for debug pagealloc if we don't enable
			it at boot time and the system will work mostly same
			with the kernel built without CONFIG_DEBUG_PAGEALLOC.
			on: enable the feature

966 967
	debugpat	[X86] Enable PAT debugging

968
	decnet.addr=	[HW,NET]
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			Format: <area>[,<node>]
			See also Documentation/networking/decnet.txt.

972 973 974 975 976 977 978
	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.
979

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	dhash_entries=	[KNL]
			Set number of hash buckets for dentry cache.
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983 984 985 986 987 988
	disable_1tb_segments [PPC]
			Disables the use of 1TB hash page table segments. This
			causes the kernel to fall back to 256MB segments which
			can be useful when debugging issues that require an SLB
			miss to occur.

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

992 993 994
	disable_radix	[PPC]
			Disable RADIX MMU mode on POWER9

995 996 997 998 999 1000 1001 1002 1003
	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.

1004 1005 1006 1007
	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.

1011 1012 1013
	disable_mtrr_cleanup [X86]
			The kernel tries to adjust MTRR layout from continuous
			to discrete, to make X server driver able to add WB
1014
			entry later. This parameter disables that.
1015

1016
	disable_mtrr_trim [X86, Intel and AMD only]
1017 1018 1019 1020 1021
			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.

1022
	disable_timer_pin_1 [X86]
1023 1024 1025
			Disable PIN 1 of APIC timer
			Can be useful to work around chipset bugs.

1026 1027
	dis_ucode_ldr	[X86] Disable the microcode loader.

1028 1029 1030 1031 1032 1033 1034 1035 1036 1037
	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.

1038 1039 1040 1041 1042 1043 1044
	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.

1045 1046 1047 1048 1049
	drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
			Broken monitors, graphic adapters, KVMs and EDIDless
			panels may send no or incorrect EDID data sets.
			This parameter allows to specify an EDID data sets
			in the /lib/firmware directory that are used instead.
1050 1051 1052 1053 1054 1055 1056 1057
			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
1058 1059 1060 1061
			name. Each connector may use a unique EDID data
			set by separating the files with a comma.  An EDID
			data set with no connector name will be used for
			any connectors not explicitly specified.
1062

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1063 1064
	dscc4.setup=	[NET]

1065 1066 1067 1068 1069
	dump_apple_properties	[X86]
			Dump name and content of EFI device properties on
			x86 Macs.  Useful for driver authors to determine
			what data is available or for reverse-engineering.

1070 1071 1072 1073 1074
	dyndbg[="val"]		[KNL,DYNAMIC_DEBUG]
	module.dyndbg[="val"]
			Enable debug messages at boot time.  See
			Documentation/dynamic-debug-howto.txt for details.

1075 1076 1077 1078
	nompx		[X86] Disables Intel Memory Protection Extensions.
			See Documentation/x86/intel_mpx.txt for more
			information about the feature.

1079 1080 1081
	nopku		[X86] Disable Memory Protection Keys CPU feature found
			in some Intel CPUs.

1082 1083 1084
	module.async_probe [KNL]
			Enable asynchronous probe on this module.

1085 1086 1087 1088 1089
	early_ioremap_debug [KNL]
			Enable debug messages in early_ioremap support. This
			is useful for tracking down temporary early mappings
			which are not unmapped.

1090
	earlycon=	[KNL] Output early console device and options.
1091

1092 1093 1094 1095
			When used with no options, the early console is
			determined by the stdout-path property in device
			tree's chosen node.

1096 1097 1098 1099 1100 1101
		cdns,<addr>[,options]
			Start an early, polled-mode console on a Cadence
			(xuartps) serial port at the specified address. Only
			supported option is baud rate. If baud rate is not
			specified, the serial port must already be setup and
			configured.
1102

1103 1104
		uart[8250],io,<addr>[,options]
		uart[8250],mmio,<addr>[,options]
1105
		uart[8250],mmio32,<addr>[,options]
1106
		uart[8250],mmio32be,<addr>[,options]
1107
		uart[8250],0x<addr>[,options]
1108 1109
			Start an early, polled-mode console on the 8250/16550
			UART at the specified I/O port or MMIO address.
1110
			MMIO inter-register address stride is either 8-bit
1111 1112 1113 1114
			(mmio) or 32-bit (mmio32 or mmio32be).
			If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
			to be equivalent to 'mmio'. 'options' are specified
			in the same format described for "console=ttyS<n>"; if
1115
			unspecified, the h/w is not initialized.
1116

1117
		pl011,<addr>
1118
		pl011,mmio32,<addr>
1119 1120 1121
			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
1122 1123 1124
			yet supported.  If 'mmio32' is specified, then only
			the driver will use only 32-bit accessors to read/write
			the device registers.
1125

1126 1127 1128 1129 1130 1131
		meson,<addr>
			Start an early, polled-mode console on a meson serial
			port at the specified address. The serial port must
			already be setup and configured. Options are not yet
			supported.

1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143
		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.

1144 1145
		smh	Use ARM semihosting calls for early console.

1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157
		s3c2410,<addr>
		s3c2412,<addr>
		s3c2440,<addr>
		s3c6400,<addr>
		s5pv210,<addr>
		exynos4210,<addr>
			Use early console provided by serial driver available
			on Samsung SoCs, requires selecting proper type and
			a correct base address of the selected UART port. The
			serial port must already be setup and configured.
			Options are not yet supported.

1158 1159 1160 1161 1162 1163 1164
		lpuart,<addr>
		lpuart32,<addr>
			Use early console provided by Freescale LP UART driver
			found on Freescale Vybrid and QorIQ LS1021A processors.
			A valid base address must be provided, and the serial
			port must already be setup and configured.

1165 1166 1167 1168 1169 1170
		armada3700_uart,<addr>
			Start an early, polled-mode console on the
			Armada 3700 serial port at the specified
			address. The serial port must already be setup
			and configured. Options are not yet supported.

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	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k]
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1172
			earlyprintk=vga
1173
			earlyprintk=efi
1174
			earlyprintk=xen
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1175
			earlyprintk=serial[,ttySn[,baudrate]]
1176
			earlyprintk=serial[,0x...[,baudrate]]
1177
			earlyprintk=ttySn[,baudrate]
1178
			earlyprintk=dbgp[debugController#]
1179
			earlyprintk=pciserial,bus:device.function[,baudrate]
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1181 1182 1183 1184
			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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1186 1187
			takes over.

1188 1189
			Only one of vga, efi, serial, or usb debug port can
			be used at a time.
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1191 1192 1193 1194 1195 1196 1197 1198
			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.

1203 1204
			The VGA and EFI output is eventually overwritten by
			the real console.
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1206 1207
			The xen output can only be used by Xen PV guests.

1208 1209 1210 1211 1212 1213 1214 1215
	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.

1216 1217 1218
	ekgdboc=	[X86,KGDB] Allow early kernel console debugging
			ekgdboc=kbd

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			This is designed to be used in conjunction with
1220 1221
			the boot argument: earlyprintk=vga

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	edd=		[EDD]
1223
			Format: {"off" | "on" | "skip[mbr]"}
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1225
	efi=		[EFI]
1226
			Format: { "old_map", "nochunk", "noruntime", "debug" }
1227 1228 1229
			old_map [X86-64]: switch to the old ioremap-based EFI
			runtime services mapping. 32-bit still uses this one by
			default.
1230 1231 1232
			nochunk: disable reading files in "chunks" in the EFI
			boot stub, as chunking can cause problems with some
			firmware implementations.
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1233
			noruntime : disable EFI runtime services support
1234
			debug: enable misc debug output
1235

1236 1237 1238 1239 1240 1241
	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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1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256
	efi_fake_mem=	nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
			Add arbitrary attribute to specific memory range by
			updating original EFI memory map.
			Region of memory which aa attribute is added to is
			from ss to ss+nn.
			If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
			is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
			attribute is added to range 0x100000000-0x180000000 and
			0x10a0000000-0x1120000000.

			Using this parameter you can do debugging of EFI memmap
			related feature. For example, you can do debugging of
			Address Range Mirroring feature even if your box
			doesn't support it.

1257 1258 1259 1260 1261 1262 1263
	efivar_ssdt=	[EFI; X86] Name of an EFI variable that contains an SSDT
			that is to be dynamically loaded by Linux. If there are
			multiple variables with the same name but with different
			vendor GUIDs, all of them will be loaded. See
			Documentation/acpi/ssdt-overlays.txt for details.


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1264 1265 1266
	eisa_irq_edge=	[PARISC,HW]
			See header of drivers/parisc/eisa.c.

1267
	elanfreq=	[X86-32]
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			See comment before function elanfreq_setup() in
1269
			arch/x86/kernel/cpu/cpufreq/elanfreq.c.
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	elevator=	[IOSCHED]
1272
			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.

1276
	elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
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			Specifies physical address of start of kernel core
1278 1279
			image elf header and optionally the size. Generally
			kexec loader will pass this option to capture kernel.
1280
			See Documentation/kdump/kdump.txt for details.
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1282 1283 1284 1285 1286
	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.

1287
	enable_timer_pin_1 [X86]
1288 1289 1290 1291 1292
			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.

1301 1302 1303 1304
	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.

1309 1310 1311 1312 1313
	evm=		[EVM]
			Format: { "fix" }
			Permit 'security.evm' to be updated regardless of
			current integrity status.

1314 1315 1316 1317 1318
	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/.
1320

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	floppy=		[HW]
1322
			See Documentation/blockdev/floppy.txt.
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1324 1325 1326 1327 1328 1329
	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.

1330 1331 1332 1333 1334 1335 1336
	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.

1337
	ftrace=[tracer]
1338
			[FTRACE] will set and start the specified tracer
1339 1340 1341
			as early as possible in order to facilitate early
			boot debugging.

1342
	ftrace_dump_on_oops[=orig_cpu]
1343
			[FTRACE] will dump the trace buffers on oops.
1344 1345 1346 1347
			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.
1348 1349 1350 1351 1352 1353

	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
1354
			tracing directory.
1355 1356 1357 1358 1359 1360

	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.
1361

1362 1363 1364 1365 1366 1367 1368
	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.

1369 1370 1371 1372 1373 1374
	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

1387 1388 1389 1390 1391 1392
	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
1394 1395 1396
			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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1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415
	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

1416 1417 1418 1419
	gpio-mockup.gpio_mockup_ranges
			[HW] Sets the ranges of gpiochip of for this device.
			Format: <start1>,<end1>,<start2>,<end2>...

1420 1421 1422 1423 1424
	hardlockup_all_cpu_backtrace=
			[KNL] Should the hard-lockup detector generate
			backtraces on all cpus.
			Format: <integer>

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1425 1426
	hashdist=	[KNL,NUMA] Large hashes allocated during boot
			are distributed across NUMA nodes.  Defaults on
1427
			for 64-bit NUMA, off otherwise.
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			Format: 0 | 1 (for off | on)
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1429 1430 1431 1432 1433 1434

	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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1440 1441 1442 1443 1444
	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.

1445 1446 1447 1448
	highres=	[KNL] Enable/disable high resolution timer mode.
			Valid parameters: "on", "off"
			Default: "on"

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1449 1450 1451
	hisax=		[HW,ISDN]
			See Documentation/isdn/README.HiSax.

1452 1453 1454 1455 1456 1457 1458 1459 1460 1461
	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

1462 1463 1464
	hpet_mmap=	[X86, HPET_MMAP] Allow userspace to mmap HPET
			registers.  Default set by CONFIG_HPET_MMAP_DEFAULT.

1465 1466
	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.
1467 1468 1469 1470
			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
1471
			(when the CPU supports the "pdpe1gb" cpuinfo flag).
1472

1473 1474
	hvc_iucv=	[S390] Number of z/VM IUCV hypervisor console (HVC)
			       terminal devices. Valid values: 0..8
1475 1476 1477
	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.
1478

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

1483 1484 1485 1486 1487 1488
	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.

1489
	i2c_bus=	[HW] Override the default board specific I2C bus speed
1490 1491
			     or register an additional I2C bus that is not
			     registered from board initialization code.
1492 1493 1494
			     Format:
			     <bus_id>,<clkrate>

1495
	i8042.debug	[HW] Toggle i8042 debug mode
1496 1497 1498 1499
	i8042.unmask_kbd_data
			[HW] Enable printing of interrupt data from the KBD port
			     (disabled by default, and as a pre-condition
			     requires that i8042.debug=1 be enabled)
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	i8042.direct	[HW] Put keyboard port into non-translated mode
1501 1502
	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
1505
	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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1508
	i8042.nomux	[HW] Don't check presence of an active multiplexing
1509
			     controller
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1510 1511
	i8042.nopnp	[HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
			     controllers
1512
	i8042.notimeout	[HW] Ignore timeout condition signalled by controller
1513 1514 1515 1516 1517 1518 1519 1520
	i8042.reset	[HW] Reset the controller during init, cleanup and
			     suspend-to-ram transitions, only during s2r
			     transitions, or never reset
			Format: { 1 | Y | y | 0 | N | n }
			1, Y, y: always reset controller
			0, N, n: don't ever reset controller
			Default: only on s2r transitions on x86; most other
			architectures force reset to be always executed
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	i8042.unlock	[HW] Unlock (ignore) the keylock
1522
	i8042.kbdreset  [HW] Reset device connected to KBD port
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	i810=		[HW,DRM]

1526 1527 1528
	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.

1537
	i915.invert_brightness=
1538 1539
			[DRM] Invert the sense of the variable that is used to
			set the brightness of the panel backlight. Normally a
1540 1541 1542 1543 1544 1545 1546 1547 1548 1549
			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
1550

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

1554 1555
	ide-core.nodma=	[HW] (E)IDE subsystem
			Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1556 1557
			.vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
			.cdrom .chs .ignore_cable are additional options
1558
			See Documentation/ide/ide.txt.
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1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571
	ide-generic.probe-mask= [HW] (E)IDE subsystem
			Format: <int>
			Probe mask for legacy ISA IDE ports.  Depending on
			platform up to 6 ports are supported, enabled by
			setting corresponding bits in the mask to 1.  The
			default value is 0x0, which has a special meaning.
			On systems that have PCI, it triggers scanning the
			PCI bus for the first and the second port, which
			are then probed.  On systems without PCI the value
			of 0x0 enables probing the two first ports as if it
			was 0x3.

1572 1573 1574
	ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
			Claim all unknown PCI IDE storage controllers.

1575
	idle=		[X86]
1576
			Format: idle=poll, idle=halt, idle=nomwait
1577 1578 1579 1580 1581
			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.
1583
			idle=nomwait: Disable mwait for CPU C-states
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1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619
	ieee754=	[MIPS] Select IEEE Std 754 conformance mode
			Format: { strict | legacy | 2008 | relaxed }
			Default: strict

			Choose which programs will be accepted for execution
			based on the IEEE 754 NaN encoding(s) supported by
			the FPU and the NaN encoding requested with the value
			of an ELF file header flag individually set by each
			binary.  Hardware implementations are permitted to
			support either or both of the legacy and the 2008 NaN
			encoding mode.

			Available settings are as follows:
			strict	accept binaries that request a NaN encoding
				supported by the FPU
			legacy	only accept legacy-NaN binaries, if supported
				by the FPU
			2008	only accept 2008-NaN binaries, if supported
				by the FPU
			relaxed	accept any binaries regardless of whether
				supported by the FPU

			The FPU emulator is always able to support both NaN
			encodings, so if no FPU hardware is present or it has
			been disabled with 'nofpu', then the settings of
			'legacy' and '2008' strap the emulator accordingly,
			'relaxed' straps the emulator for both legacy-NaN and
			2008-NaN, whereas 'strict' enables legacy-NaN only on
			legacy processors and both NaN encodings on MIPS32 or
			MIPS64 CPUs.

			The setting for ABS.fmt/NEG.fmt instruction execution
			mode generally follows that for the NaN encoding,
			except where unsupported by hardware.

1620 1621 1622
	ignore_loglevel	[KNL]
			Ignore loglevel setting - this will print /all/
			kernel messages to the console. Useful for debugging.
1623 1624 1625
			We also add it as printk module parameter, so users
			could change it dynamically, usually by
			/sys/module/printk/parameters/ignore_loglevel.
1626

1627 1628 1629 1630 1631
	ignore_rlimit_data
			Ignore RLIMIT_DATA setting for data mappings,
			print warning at first misuse.  Can be changed via
			/sys/module/kernel/parameters/ignore_rlimit_data.

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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
1636
			Format: { "off" | "enforce" | "fix" | "log" }
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			default: "enforce"

1639 1640 1641 1642
	ima_appraise_tcb [IMA]
			The builtin appraise policy appraises all files
			owned by uid=0.

1643
	ima_hash=	[IMA]
1644 1645
			Format: { md5 | sha1 | rmd160 | sha256 | sha384
				   | sha512 | ... }
1646 1647
			default: "sha1"

1648 1649 1650
			The list of supported hash algorithms is defined
			in crypto/hash_info.h.

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	ima_policy=	[IMA]
			The builtin measurement policy to load during IMA
			setup.  Specyfing "tcb" as the value, measures all
			programs exec'd, files mmap'd for exec, and all files
			opened with the read mode bit set by either the
			effective uid (euid=0) or uid=0.
			Format: "tcb"

	ima_tcb		[IMA] Deprecated.  Use ima_policy= instead.
1660 1661 1662 1663 1664
			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.

1665 1666
	ima_template=   [IMA]
			Select one of defined IMA measurements template formats.
1667
			Formats: { "ima" | "ima-ng" | "ima-sig" }
1668 1669
			Default: "ima-ng"

1670 1671 1672 1673
	ima_template_fmt=
	                [IMA] Define a custom template format.
			Format: { "field1|...|fieldN" }

1674 1675 1676 1677 1678 1679 1680 1681 1682
	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.

1683 1684 1685 1686 1687 1688 1689 1690
	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.

1700 1701 1702 1703
	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

1706 1707 1708 1709 1710
	init_pkru=	[x86] Specify the default memory protection keys rights
			register contents for all processes.  0x55555554 by
			default (disallow access to all but pkey 0).  Can
			override in debugfs after boot.

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

1714 1715
	int_pln_enable  [x86] Enable power limit notification interrupt

1716 1717 1718 1719 1720
	integrity_audit=[IMA]
			Format: { "0" | "1" }
			0 -- basic integrity auditing messages. (Default)
			1 -- additional integrity auditing messages.

1721
	intel_iommu=	[DMAR] Intel IOMMU driver (DMAR) option
1722 1723
		on
			Enable intel iommu driver.
1724 1725 1726 1727 1728 1729 1730 1731
		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.
1732 1733
		forcedac [x86_64]
			With this option iommu will not optimize to look
1734
			for io virtual address below 32-bit forcing dual
1735
			address cycle on pci bus for cards supporting greater
1736 1737
			than 32-bit addressing. The default is to look
			for translation below 32-bit and if not available
1738
			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.
1743 1744 1745 1746
		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.
1747 1748 1749 1750 1751 1752
		ecs_off [Default Off]
			By default, extended context tables will be supported if
			the hardware advertises that it has support both for the
			extended tables themselves, and also PASID support. With
			this option set, extended tables will not be used even
			on hardware which claims to support them.
1753 1754 1755

	intel_idle.max_cstate=	[KNL,HW,ACPI,X86]
			0	disables intel_idle and fall back on acpi_idle.
1756
			1 to 9	specify maximum depth of C-state.
1757

1758 1759 1760 1761
	intel_pstate=  [X86]
		       disable
		         Do not enable intel_pstate as the default
		         scaling driver for the supported processors
1762 1763 1764 1765 1766 1767 1768 1769 1770
		       force
			 Enable intel_pstate on systems that prohibit it by default
			 in favor of acpi-cpufreq. Forcing the intel_pstate driver
			 instead of acpi-cpufreq may disable platform features, such
			 as thermal controls and power capping, that rely on ACPI
			 P-States information being indicated to OSPM and therefore
			 should be used with caution. This option does not work with
			 processors that aren't supported by the intel_pstate driver
			 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
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		       no_hwp
		         Do not enable hardware P state control (HWP)
			 if available.
1774 1775 1776
		hwp_only
			Only load intel_pstate on systems which support
			hardware P state control (HWP) if available.
1777
		support_acpi_ppc
1778 1779 1780 1781
			Enforce ACPI _PPC performance limits. If the Fixed ACPI
			Description Table, specifies preferred power management
			profile as "Enterprise Server" or "Performance Server",
			then this feature is turned on by default.
1782

1783 1784 1785 1786
	intremap=	[X86-64, Intel-IOMMU]
			on	enable Interrupt Remapping (default)
			off	disable Interrupt Remapping
			nosid	disable Source ID checking
1787 1788
			no_x2apic_optout
				BIOS x2APIC opt-out request will be ignored
1789
			nopost	disable Interrupt Posting
1790

1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805
	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
1806
		pt		[x86, IA-64]
1807 1808
		nobypass	[PPC/POWERNV]
			Disable IOMMU bypass, using IOMMU for PCI devices.
1809

1810 1811 1812 1813 1814

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

1815
	io_delay=	[X86] I/O delay method
1816 1817 1818 1819
		0x80
			Standard port 0x80 based delay
		0xed
			Alternate port 0xed based delay (needed on some systems)
1820
		udelay
1821 1822 1823
			Simple two microseconds delay
		none
			No delay
1824

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	ip=		[IP_PNP]
1826
			See Documentation/filesystems/nfs/nfsroot.txt.
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1828
	irqaffinity=	[SMP] Set the default irq affinity mask
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			The argument is a cpu list, as described above.
1830

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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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1844 1845

	isolcpus=	[KNL,SMP] Isolate CPUs from the general scheduler.
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			The argument is a cpu list, as described above.
1847

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			This option can be used to specify one or more CPUs
			to isolate from the general SMP balancing and scheduling
1850 1851
			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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1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875
	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

1876 1877 1878 1879 1880 1881 1882
	ivrs_acpihid	[HW,X86_64]
			Provide an override to the ACPI-HID:UID<->DEVICE-ID
			mapping provided in the IVRS ACPI table. For
			example, to map UART-HID:UID AMD0020:0 to
			PCI device 00:14.5 write the parameter as:
				ivrs_acpihid[00:14.5]=AMD0020:0

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

1886 1887 1888 1889
	nokaslr		[KNL]
			When CONFIG_RANDOMIZE_BASE is set, this disables
			kernel and module base offset ASLR (Address Space
			Layout Randomization).
1890

1891 1892
	keepinitrd	[HW,ARM]

1893 1894 1895
	kernelcore=	[KNL,X86,IA-64,PPC]
			Format: nn[KMGTPE] | "mirror"
			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
1903
			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.

1911 1912 1913 1914 1915 1916 1917
			Instead of specifying the amount of memory (nn[KMGTPE]),
			you can specify "mirror" option. In case "mirror"
			option is specified, mirrored (reliable) memory is used
			for non-movable allocations and remaining memory is used
			for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
			so you can NOT specify nn[KMGTPE] and "mirror" at the same
			time.
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1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929
	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.

1930
	kgdboc=		[KGDB,HW] kgdb over consoles.
1931 1932
			Requires a tty driver that supports console polling,
			or a supported polling keyboard driver (non-usb).
1933 1934 1935 1936 1937 1938
			 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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1940 1941 1942
	kgdbwait	[KGDB] Stop kernel execution and enter the
			kernel debugger at the earliest opportunity.

1943 1944 1945 1946
	kmac=		[MIPS] korina ethernet MAC address.
			Configure the RouterBoard 532 series on-chip
			Ethernet adapter MAC address.

1947 1948 1949
	kmemleak=	[KNL] Boot-time kmemleak enable/disable
			Valid arguments: on, off
			Default: on
1950 1951
			Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
			the default is off.
1952

1953 1954 1955 1956 1957 1958 1959
	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)

1960 1961 1962
	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
			Default is 0 (don't ignore, but inject #GP)

1963 1964
	kvm.mmu_audit=	[KVM] This is a R/W parameter which allows audit
			KVM MMU at runtime.
1965 1966 1967
			Default is 0 (off)

	kvm-amd.nested=	[KVM,AMD] Allow nested virtualization in KVM/SVM.
1968
			Default is 1 (enabled)
1969 1970 1971

	kvm-amd.npt=	[KVM,AMD] Disable nested paging (virtualized MMU)
			for all guests.
1972
			Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

	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)

1986 1987 1988 1989
	kvm-intel.nested=
			[KVM,Intel] Enable VMX nesting (nVMX).
			Default is 0 (disabled)

1990 1991 1992 1993 1994 1995 1996 1997 1998
	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]

2001 2002
	l3cr=		[PPC]

2003
	lapic		[X86-32,APIC] Enable the local APIC even if BIOS
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			disabled it.
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2006 2007 2008 2009
	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.

2010
	lapic_timer_c2_ok	[X86,APIC] trust the local apic timer
2011
			in C2 power state.
2012

2013 2014 2015 2016
	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
2017
			libata.dma=4	  Compact Flash DMA only
2018 2019
			Combinations also work, so libata.dma=3 enables DMA
			for disks and CDROMs, but not CFs.
2020

2021 2022 2023
	libata.ignore_hpa=	[LIBATA] Ignore HPA limit
			libata.ignore_hpa=0	  keep BIOS limits (default)
			libata.ignore_hpa=1	  ignore limits, using full disk
2024

2025 2026 2027 2028
	libata.noacpi	[LIBATA] Disables use of ACPI in libata suspend/resume
			when set.
			Format: <int>

2029 2030
	libata.force=	[LIBATA] Force configurations.  The format is comma
			separated list of "[ID:]VAL" where ID is
2031
			PORT[.DEVICE].  PORT and DEVICE are decimal numbers
2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060
			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.

2061 2062
			* [no]ncqtrim: Turn off queued DSM TRIM.

2063 2064 2065
			* nohrst, nosrst, norst: suppress hard, soft
                          and both resets.

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

2069 2070
			* dump_id: dump IDENTIFY data.

2071 2072
			* atapi_dmadir: Enable ATAPI DMADIR bridge support

2073 2074
			* disable: Disable this device.

2075 2076 2077
			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.
2079

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	load_ramdisk=	[RAM] List of ramdisks to load from floppy
2081
			See Documentation/blockdev/ramdisk.txt.
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	lockd.nlm_grace_period=P  [NFS] Assign grace period.
			Format: <integer>
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2086 2087 2088 2089 2090 2091 2092 2093
	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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	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

2155
	log_buf_len=n[KMG]	Sets the size of the printk ring buffer,
2156 2157 2158 2159 2160 2161
			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>

2202
	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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2206 2207 2208 2209
	machtype=	[Loongson] Share the same kernel image file between different
			 yeeloong laptop.
			Example: machtype=lemote-yeeloong-2f-7inch

2210 2211
	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
2214 2215 2216 2217 2218 2219 2220
			will bring up during bootup.  maxcpus=n : n >= 0 limits
			the kernel to bring up 'n' processors. Surely after
			bootup you can bring up the other plugged cpu by executing
			"echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
			only takes effect during system bootup.
			While n=0 is a special case, it is equivalent to "nosmp",
			which also disables the IO APIC.
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2222 2223 2224 2225 2226 2227
	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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2229
	mce		[X86-32] Machine Check Exception
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	mce=option	[X86-64] See Documentation/x86/x86_64/boot-options.txt
2232

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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.
2243 2244 2245 2246
			[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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2248
	mem=nopentium	[BUGS=X86-32] Disable usage of 4MB pages for kernel
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			memory.

2251 2252 2253 2254
	memchunk=nn[KMG]
			[KNL,SH] Allow user to override the default size for
			per-device physically contiguous DMA buffers.

2255 2256 2257 2258 2259 2260 2261 2262
        memhp_default_state=online/offline
			[KNL] Set the initial state for the memory hotplug
			onlining policy. If not specified, the default value is
			set according to the
			CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
			option.
			See Documentation/memory-hotplug.txt.

2263
	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]
2270 2271
			[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.
2275
			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.
2279
			Region of memory to be reserved is from ss to ss+nn.
2280 2281 2282 2283
			Example: Exclude memory from 0x18690000-0x1869ffff
			         memmap=64K$0x18690000
			         or
			         memmap=0x10000$0x18690000
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2285 2286 2287 2288 2289 2290
	memmap=nn[KMG]!ss[KMG]
			[KNL,X86] Mark specific memory as protected.
			Region of memory to be used, from ss to ss+nn.
			The memory region may be marked as e820 type 12 (0xc)
			and is NVDIMM or ADR memory.

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	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.

2314
	memtest=	[KNL,X86,ARM] Enable memtest
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			Format: <integer>
			default : 0 <disable>
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			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.

2327 2328 2329 2330
	mfgpt_irq=	[IA-32] Specify the IRQ to use for the
			Multi-Function General Purpose Timers on AMD Geode
			platforms.

2331 2332 2333 2334 2335
	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]

2338 2339 2340
	min_addr=nn[KMG]	[KNL,BOOT,ia64] All physical memory below this
			physical address is ignored.

2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361
	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

2362 2363 2364 2365 2366 2367 2368 2369
	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.
2373
			Note that if CONFIG_MODULE_SIG_FORCE is set, that
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			is always true, so this option does nothing.

2376 2377 2378
	module_blacklist=  [KNL] Do not load a comma-separated list of
			modules.  Useful for debugging problem modules.

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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

2390
	movablecore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
2391 2392 2393 2394 2395 2396 2397 2398 2399
			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.

2400 2401 2402
	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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	MTD_Region=	[MTD] Format:
			<name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
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	mtdparts=	[MTD]
2410
			See drivers/mtd/cmdlinepart.c.
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2412 2413 2414 2415
	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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	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.

2426 2427 2428 2429 2430
	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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			[HW] Make the MicroTouch USB driver use raw coordinates
			('y', default) or cooked coordinates ('n')
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2435
	mtrr_chunk_size=nn[KMG] [X86]
2436
			used for mtrr cleanup. It is largest continuous chunk
2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451
			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.

2461 2462 2463 2464
	nf_conntrack.acct=
			[NETFILTER] Enable connection tracking flow accounting
			0 to disable accounting
			1 to enable accounting
2465
			Default value is 0.
2466

2467
	nfsaddrs=	[NFS] Deprecated.  Use ip= instead.
2468
			See Documentation/filesystems/nfs/nfsroot.txt.
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	nfsroot=	[NFS] nfs root filesystem for disk-less boxes.
2471
			See Documentation/filesystems/nfs/nfsroot.txt.
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2473 2474 2475
	nfsrootdebug	[NFS] enable nfsroot debugging messages.
			See Documentation/filesystems/nfs/nfsroot.txt.

2476 2477 2478 2479 2480
	nfs.callback_nr_threads=
			[NFSv4] set the total number of threads that the
			NFS client will assign to service NFSv4 callback
			requests.

2481 2482 2483 2484
	nfs.callback_tcpport=
			[NFS] set the TCP port on which the NFSv4 callback
			channel should listen.

2485 2486 2487 2488 2489 2490 2491 2492
	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.

2493 2494 2495 2496
	nfs.idmap_cache_timeout=
			[NFS] set the maximum lifetime for idmapper cache
			entries.

2497 2498 2499 2500 2501 2502 2503
	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.

2504 2505 2506 2507 2508 2509 2510
	nfs.max_session_cb_slots=
			[NFSv4.1] Sets the maximum number of session
			slots the client will assign to the callback
			channel. This determines the maximum number of
			callbacks the client will process in parallel for
			a particular server.

2511 2512 2513 2514 2515 2516 2517 2518
	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.

2519
	nfs.nfs4_disable_idmapping=
2520 2521 2522 2523 2524 2525 2526 2527 2528 2529 2530
			[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'.
2531 2532 2533 2534 2535
	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.
2536

2537 2538 2539 2540 2541 2542 2543
	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.
2544 2545 2546 2547 2548 2549 2550 2551 2552 2553 2554 2555
	
	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.
2556

2557 2558 2559 2560 2561 2562 2563 2564 2565
	nfs4.layoutstats_timer =
			[NFSv4.2] Change the rate at which the kernel sends
			layoutstats to the pNFS metadata server.

			Setting this to value to 0 causes the kernel to use
			whatever value is the default set by the layout
			driver. A non-zero value sets the minimum interval
			in seconds between layoutstats transmissions.

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J. Bruce Fields 已提交
2566 2567 2568 2569 2570 2571
	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.
2572

2573 2574 2575 2576 2577 2578
	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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Paul Mundt 已提交
2579
	nmi_debug=	[KNL,AVR32,SH] Specify one or more actions to take
H
Haavard Skinnemoen 已提交
2580 2581 2582
			when a NMI is triggered.
			Format: [state][,regs][,debounce][,die]

2583
	nmi_watchdog=	[KNL,BUGS=X86] Debugging features for SMP kernels
2584
			Format: [panic,][nopanic,][num]
2585
			Valid num: 0 or 1
2586 2587
			0 - turn hardlockup detector in nmi_watchdog off
			1 - turn hardlockup detector in nmi_watchdog on
2588
			When panic is specified, panic when an NMI watchdog
2589
			timeout occurs (or 'nopanic' to override the opposite
2590 2591
			default). To disable both hard and soft lockup detectors,
			please see 'nowatchdog'.
2592 2593
			This is useful when you use a panic=... timeout and
			need the box quickly up again.
L
Linus Torvalds 已提交
2594

2595 2596 2597 2598 2599
	netpoll.carrier_timeout=
			[NET] Specifies amount of time (in seconds) that
			netpoll should wait for a carrier. By default netpoll
			waits 4 seconds.

2600
	no387		[BUGS=X86-32] Tells the kernel to use the 387 maths
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Linus Torvalds 已提交
2601 2602 2603
			emulation library even if a 387 maths coprocessor
			is present.

2604 2605 2606 2607 2608 2609 2610 2611 2612
	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.
2613 2614 2615 2616 2617
			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.
2618

C
Christoph Lameter 已提交
2619 2620 2621
	noaliencache	[MM, NUMA, SLAB] Disables the allocation of alien
			caches in the slab allocator.  Saves per-node memory,
			but will impact performance.
2622

R
Randy Dunlap 已提交
2623 2624
	noalign		[KNL,ARM]

L
Linus Torvalds 已提交
2625 2626 2627
	noapic		[SMP,APIC] Tells the kernel to not make use of any
			IOAPICs that may be present in the system.

2628 2629
	noautogroup	Disable scheduler automatic task group creation.

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Linus Torvalds 已提交
2630 2631 2632 2633
	nobats		[PPC] Do not use BATs for mapping kernel lowmem
			on "Classic" PPC cores.

	nocache		[ARM]
R
Randy Dunlap 已提交
2634

2635 2636
	noclflush	[BUGS=X86] Don't use the CLFLUSH instruction

2637 2638
	nodelayacct	[KNL] Disable per-task delay accounting

2639 2640
	nodsp		[SH] Disable hardware DSP at boot time.

2641
	noefi		Disable EFI runtime services support.
2642

L
Linus Torvalds 已提交
2643 2644
	noexec		[IA-64]

2645
	noexec		[X86]
J
Jiri Slaby 已提交
2646
			On X86-32 available only on PAE configured kernels.
L
Linus Torvalds 已提交
2647
			noexec=on: enable non-executable mappings (default)
J
Jiri Slaby 已提交
2648 2649
			noexec=off: disable non-executable mappings

2650 2651 2652 2653
	nosmap		[X86]
			Disable SMAP (Supervisor Mode Access Prevention)
			even if it is supported by processor.

2654
	nosmep		[X86]
2655
			Disable SMEP (Supervisor Mode Execution Prevention)
2656 2657
			even if it is supported by processor.

J
Jiri Slaby 已提交
2658 2659 2660 2661 2662 2663
	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
L
Linus Torvalds 已提交
2664

2665
	nofpu		[MIPS,SH] Disable hardware FPU at boot time.
2666

2667
	nofxsr		[BUGS=X86-32] Disables x86 floating point extended
2668 2669
			register save and restore. The kernel will only save
			legacy floating-point registers on task switch.
L
Linus Torvalds 已提交
2670

2671 2672
	nohugeiomap	[KNL,x86] Disable kernel huge I/O mappings.

2673 2674 2675
	nosmt		[KNL,S390] Disable symmetric multithreading (SMT).
			Equivalent to smt=1.

2676 2677 2678 2679
	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.

2680 2681 2682 2683 2684 2685 2686 2687 2688 2689 2690 2691 2692 2693 2694
	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.

2695 2696 2697
	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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Randy Dunlap 已提交
2698

2699 2700 2701 2702
	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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Linus Torvalds 已提交
2703 2704 2705 2706 2707 2708 2709
	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.

2710 2711
	nohibernate	[HIBERNATION] Disable hibernation and resume.

2712 2713 2714 2715
	nohz=		[KNL] Boottime enable/disable dynamic ticks
			Valid arguments: on, off
			Default: on

2716
	nohz_full=	[KNL,BOOT]
N
Noam Camus 已提交
2717
			The argument is a cpu list, as described above.
2718
			In kernels built with CONFIG_NO_HZ_FULL=y, set
2719
			the specified list of CPUs whose tick will be stopped
2720 2721
			whenever possible. The boot CPU will be forced outside
			the range to maintain the timekeeping.
2722 2723
			The CPUs in this range must also be included in the
			rcu_nocbs= set.
2724

2725 2726
	noiotrap	[SH] Disables trapped I/O port accesses.

2727
	noirqdebug	[X86-32] Disables the code which attempts to detect and
L
Linus Torvalds 已提交
2728 2729
			disable unhandled interrupt sources.

2730
	no_timer_check	[X86,APIC] Disables the code which tests for
2731 2732
			broken timer IRQ sources.

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Linus Torvalds 已提交
2733 2734 2735 2736 2737
	noisapnp	[ISAPNP] Disables ISA PnP code.

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

2738 2739
	nointremap	[X86-64, Intel-IOMMU] Do not enable interrupt
			remapping.
2740
			[Deprecated - use intremap=off]
2741

L
Linus Torvalds 已提交
2742 2743
	nointroute	[IA-64]

2744 2745
	noinvpcid	[X86] Disable the INVPCID cpu feature.

2746
	nojitter	[IA-64] Disables jitter checking for ITC timers.
2747

2748 2749
	no-kvmclock	[X86,KVM] Disable paravirtualized KVM clock driver

2750 2751 2752
	no-kvmapf	[X86,KVM] Disable paravirtualized asynchronous page
			fault handling.

2753 2754 2755 2756
	no-vmw-sched-clock
			[X86,PV_OPS] Disable paravirtualized VMware scheduler
			clock and use the default one.

2757 2758 2759 2760
	no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
			steal time is computed, but won't influence scheduler
			behaviour

2761
	nolapic		[X86-32,APIC] Do not enable or use the local APIC.
L
Linus Torvalds 已提交
2762

2763
	nolapic_timer	[X86-32,APIC] Do not use the local APIC timer.
2764

L
Linus Torvalds 已提交
2765
	noltlbs		[PPC] Do not use large page/tlb entries for kernel
2766
			lowmem mapping on PPC40x and PPC8xx
L
Linus Torvalds 已提交
2767

2768 2769
	nomca		[IA-64] Disable machine check abort handling

2770
	nomce		[X86-32] Disable Machine Check Exception
2771

2772 2773 2774
	nomfgpt		[X86-32] Disable Multi-Function General Purpose
			Timer usage (for AMD Geode machines).

2775 2776 2777 2778
	nonmi_ipi	[X86] Disable using NMI IPIs during panic/reboot to
			shutdown the other cpus.  Instead use the REBOOT_VECTOR
			irq.

2779 2780
	nomodule	Disable module load

2781 2782 2783
	nopat		[X86] Disable PAT (page attribute table extension of
			pagetables) support.

2784 2785 2786
	norandmaps	Don't use address space randomization.  Equivalent to
			echo 0 > /proc/sys/kernel/randomize_va_space

2787
	noreplace-paravirt	[X86,IA-64,PV_OPS] Don't patch paravirt_ops
2788

2789
	noreplace-smp	[X86-32,SMP] Don't replace SMP instructions
2790 2791
			with UP alternatives

2792 2793 2794 2795
	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.
2796

R
Randy Dunlap 已提交
2797 2798 2799
	noresume	[SWSUSP] Disables resume and restores original swap
			space.

L
Linus Torvalds 已提交
2800 2801 2802 2803 2804 2805
	no-scroll	[VGA] Disables scrollback.
			This is required for the Braillex ib80-piezo Braille
			reader made by F.H. Papenmeier (Germany).

	nosbagart	[IA-64]

2806
	nosep		[BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2807

2808 2809
	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel,
			and disable the IO APIC.  legacy for "maxcpus=0".
L
Linus Torvalds 已提交
2810

2811 2812
	nosoftlockup	[KNL] Disable the soft-lockup detector.

L
Linus Torvalds 已提交
2813 2814
	nosync		[HW,M68K] Disables sync negotiation for all devices.

2815
	notsc		[BUGS=X86-32] Disable Time Stamp Counter
L
Linus Torvalds 已提交
2816

2817 2818
	nowatchdog	[KNL] Disable both lockup detectors, i.e.
                        soft-lockup and NMI watchdog (hard-lockup).
2819

L
Linus Torvalds 已提交
2820
	nowb		[ARM]
R
Randy Dunlap 已提交
2821

2822 2823
	nox2apic	[X86-64,APIC] Do not enable x2APIC mode.

2824 2825 2826 2827 2828 2829 2830 2831 2832 2833 2834 2835 2836 2837
	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.

2838
	nptcg=		[IA-64] Override max number of concurrent global TLB
2839 2840 2841
			purges which is reported from either PAL_VM_SUMMARY or
			SAL PALO.

2842 2843
	nr_cpus=	[SMP] Maximum number of processors that	an SMP kernel
			could support.  nr_cpus=n : n >= 1 limits the kernel to
2844 2845 2846 2847 2848 2849
			support 'n' processors. It could be larger than the
			number of already plugged CPU during bootup, later in
			runtime you can physically add extra cpu until it reaches
			n. So during boot up some boot time memory for per-cpu
			variables need be pre-allocated for later physical cpu
			hot plugging.
2850

2851 2852
	nr_uarts=	[SERIAL] maximum number of UARTs to be registered.

2853 2854 2855
	numa_balancing=	[KNL,X86] Enable or disable automatic NUMA balancing.
			Allowed values are enable and disable

2856 2857 2858 2859 2860
	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.

2861 2862 2863 2864
	ohci1394_dma=early	[HW] enable debugging via the ohci1394 driver.
			See Documentation/debugging-via-ohci1394.txt for more
			info.

2865 2866 2867 2868 2869 2870 2871
	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!

2872 2873 2874 2875 2876
	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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2877 2878 2879
	oprofile.timer=	[HW]
			Use timer interrupt instead of performance counters

2880 2881 2882
	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.
2883 2884
			Format: { arch_perfmon }
			arch_perfmon: [X86] Force use of architectural
2885 2886
				perfmon on Intel CPUs instead of the
				CPU specific event set.
2887 2888 2889
			timer: [X86] Force use of architectural NMI
				timer mode (see also oprofile.timer
				for generic hr timer mode)
2890

2891 2892 2893
	oops=panic	Always panic on oopses. Default is to just kill the
			process, but there is a small probability of
			deadlocking the machine.
2894 2895 2896
			This will also cause panics on machine check exceptions.
			Useful together with panic=30 to trigger a reboot.

2897 2898 2899
	OSS		[HW,OSS]
			See Documentation/sound/oss/oss-parameters.txt

2900 2901 2902 2903 2904 2905
	page_owner=	[KNL] Boot-time page_owner enabling option.
			Storage of the information about who allocated
			each page is disabled in default. With this switch,
			we can turn it on.
			on: enable the feature

2906 2907 2908 2909 2910
	page_poison=	[KNL] Boot-time parameter changing the state of
			poisoning on the buddy allocator.
			off: turn off poisoning
			on: turn on poisoning

2911
	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
2912 2913 2914
			timeout > 0: seconds before rebooting
			timeout = 0: wait forever
			timeout < 0: reboot immediately
L
Linus Torvalds 已提交
2915 2916
			Format: <timeout>

P
Prarit Bhargava 已提交
2917 2918 2919
	panic_on_warn	panic() instead of WARN().  Useful to cause kdump
			on a WARN().

2920 2921 2922 2923 2924 2925 2926 2927
	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.

L
Linus Torvalds 已提交
2928 2929 2930 2931 2932
	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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Randy Dunlap 已提交
2933 2934 2935 2936 2937 2938 2939 2940 2941 2942 2943 2944 2945 2946 2947 2948 2949 2950 2951 2952 2953 2954
			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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2955 2956
			Format: [spp|ps2|epp|ecp|ecpepp]

2957 2958 2959 2960 2961
	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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2962 2963 2964 2965
	pcbit=		[HW,ISDN]

	pcd.		[PARIDE]
			See header of drivers/block/paride/pcd.c.
2966
			See also Documentation/blockdev/paride.txt.
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2967

R
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2968
	pci=option[,option...]	[PCI] various PCI subsystem options:
2969 2970
		earlydump	[X86] dump PCI config space before the kernel
			        changes anything
2971
		off		[X86] don't probe for the PCI bus
2972
		bios		[X86-32] force use of PCI BIOS, don't access
R
Randy Dunlap 已提交
2973 2974
				the hardware directly. Use this if your machine
				has a non-standard PCI host bridge.
2975
		nobios		[X86-32] disallow use of PCI BIOS, only direct
R
Randy Dunlap 已提交
2976 2977 2978
				hardware access methods are allowed. Use this
				if you experience crashes upon bootup and you
				suspect they are caused by the BIOS.
2979 2980 2981 2982 2983 2984 2985 2986 2987 2988
		conf1		[X86] Force use of PCI Configuration Access
				Mechanism 1 (config address in IO port 0xCF8,
				data in IO port 0xCFC, both 32-bit).
		conf2		[X86] Force use of PCI Configuration Access
				Mechanism 2 (IO port 0xCF8 is an 8-bit port for
				the function, IO port 0xCFA, also 8-bit, sets
				bus number. The config space is then accessed
				through ports 0xC000-0xCFFF).
				See http://wiki.osdev.org/PCI for more info
				on the configuration access mechanisms.
R
Randy Dunlap 已提交
2989 2990 2991
		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.
2992 2993
		nodomains	[PCI] Disable support for multiple PCI
				root domains (aka PCI segments, in ACPI-speak).
2994
		nommconf	[X86] Disable use of MMCONFIG for PCI
2995
				Configuration
2996 2997 2998
		check_enable_amd_mmconf [X86] check for and enable
				properly configured MMIO access to PCI
				config space on AMD family 10h CPU
2999 3000 3001
		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.
3002 3003 3004
		noioapicquirk	[APIC] Disable all boot interrupt quirks.
				Safety option to keep boot IRQs enabled. This
				should never be necessary.
3005 3006 3007 3008
		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.
3009 3010 3011 3012
		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.
3013
		biosirq		[X86-32] Use PCI BIOS calls to get the interrupt
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3014 3015 3016 3017 3018 3019 3020
				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.
3021
		rom		[X86] Assign address space to expansion ROMs.
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3022 3023 3024
				Use with caution as certain devices share
				address decoders between ROMs and other
				resources.
3025
		norom		[X86] Do not assign address space to
3026 3027
				expansion ROMs that do not already have
				BIOS assigned address ranges.
3028 3029
		nobar		[X86] Do not assign address space to the
				BARs that weren't assigned by the BIOS.
3030
		irqmask=0xMMMM	[X86] Set a bit mask of IRQs allowed to be
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3031 3032 3033
				assigned automatically to PCI devices. You can
				make the kernel exclude IRQs of your ISA cards
				this way.
3034
		pirqaddr=0xAAAAA	[X86] Specify the physical address
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3035 3036 3037
				of the PIRQ table (normally generated
				by the BIOS) if it is outside the
				F0000h-100000h range.
3038
		lastbus=N	[X86] Scan all buses thru bus #N. Can be
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3039 3040 3041
				useful if the kernel is unable to find your
				secondary buses and you want to tell it
				explicitly which ones they are.
3042
		assign-busses	[X86] Always assign all PCI bus
R
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3043 3044
				numbers ourselves, overriding
				whatever the firmware may have done.
3045
		usepirqmask	[X86] Honor the possible IRQ mask stored
R
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3046 3047 3048 3049 3050
				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.
3051
		noacpi		[X86] Do not use ACPI for IRQ routing
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3052
				or for PCI scanning.
3053 3054 3055 3056 3057 3058
		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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3059 3060 3061 3062
		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.
3063 3064
		skip_isa_align	[X86] do not align io start addr, so can
				handle more pci cards
3065 3066 3067 3068 3069
		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.
3070 3071 3072 3073
		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.
3074 3075 3076 3077 3078 3079 3080 3081 3082 3083 3084 3085 3086 3087 3088
		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.
3089 3090 3091 3092 3093 3094
		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.
3095 3096 3097
		resource_alignment=
				Format:
				[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3098 3099
				[<order of align>@]pci:<vendor>:<device>\
						[:<subvendor>:<subdevice>][; ...]
3100 3101 3102 3103 3104 3105
				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.
3106 3107 3108 3109
				To specify the alignment for several
				instances of a device, the PCI vendor,
				device, subvendor, and subdevice may be
				specified, e.g., 4096@pci:8086:9c22:103c:198f
3110 3111 3112 3113 3114 3115
		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.
3116 3117 3118 3119 3120 3121
		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.
3122 3123 3124
		hpbussize=nn	The minimum amount of additional bus numbers
				reserved for buses below a hotplug bridge.
				Default is 1.
3125 3126 3127 3128 3129 3130 3131
		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
3132
		noari		do not use PCIe ARI.
3133 3134 3135
		pcie_scan_all	Scan all possible PCIe devices.  Otherwise we
				only look for one device below a PCIe downstream
				port.
3136

3137 3138 3139 3140 3141 3142
	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.

3143 3144 3145 3146
	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).

3147
	pcie_ports=	[PCIE] PCIe ports handling:
3148 3149 3150 3151 3152
		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.
3153 3154 3155
		compat	Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
			ports driver.

3156 3157 3158 3159
	pcie_port_pm=	[PCIE] PCIe port power management handling:
		off	Disable power management of all PCIe ports
		force	Forcibly enable power management of all PCIe ports

3160
	pcie_pme=	[PCIE,PM] Native PCIe PME signaling options:
3161
		nomsi	Do not use MSI for native PCIe PME signaling (this makes
3162
			all PCIe root ports use INTx for all services).
3163

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Linus Torvalds 已提交
3164 3165
	pcmv=		[HW,PCMCIA] BadgePAD 4

3166 3167 3168 3169 3170 3171 3172
	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.

L
Linus Torvalds 已提交
3173
	pd.		[PARIDE]
3174
			See Documentation/blockdev/paride.txt.
L
Linus Torvalds 已提交
3175 3176 3177 3178 3179 3180

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

3181
	percpu_alloc=	Select which percpu first chunk allocator to use.
3182 3183 3184 3185 3186
			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.
3187

L
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3188
	pf.		[PARIDE]
3189
			See Documentation/blockdev/paride.txt.
L
Linus Torvalds 已提交
3190 3191

	pg.		[PARIDE]
3192
			See Documentation/blockdev/paride.txt.
L
Linus Torvalds 已提交
3193 3194

	pirq=		[SMP,APIC] Manual mp-table setup
U
Uwe Hermann 已提交
3195
			See Documentation/x86/i386/IO-APIC.txt.
L
Linus Torvalds 已提交
3196 3197 3198 3199 3200

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

3201
	pmtmr=		[X86] Manual setup of pmtmr I/O Port.
3202 3203 3204
			Override pmtimer IOPort with a hex value.
			e.g. pmtmr=0x508

3205 3206 3207 3208 3209 3210
	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.
3211

L
Linus Torvalds 已提交
3212 3213 3214 3215 3216 3217 3218 3219 3220 3221 3222 3223 3224
	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
R
Randy Dunlap 已提交
3225
			Ranges are in pairs (I/O port base and size).
L
Linus Torvalds 已提交
3226 3227

	pnp_reserve_mem=
R
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3228 3229
			[ISAPNP] Exclude memory regions for the
			autoconfiguration.
L
Linus Torvalds 已提交
3230 3231
			Ranges are in pairs (memory base and size).

3232 3233 3234 3235 3236 3237
	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>....

3238 3239 3240 3241 3242 3243
	ppc_strict_facility_enable
			[PPC] This option catches any kernel floating point,
			Altivec, VSX and SPE outside of regions specifically
			allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
			There is some performance impact when enabling this.

I
Ingo Molnar 已提交
3244 3245
	print-fatal-signals=
			[KNL] debug: print fatal signals
3246 3247 3248 3249 3250 3251 3252 3253 3254

			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".

I
Ingo Molnar 已提交
3255 3256
			default: off.

3257 3258 3259 3260 3261 3262
	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

3263 3264 3265 3266 3267 3268 3269
	printk.devkmsg={on,off,ratelimit}
			Control writing to /dev/kmsg.
			on - unlimited logging to /dev/kmsg from userspace
			off - logging to /dev/kmsg disabled
			ratelimit - ratelimit the logging
			Default: ratelimit

3270 3271 3272
	printk.time=	Show timing data prefixed to each printk message line
			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)

3273 3274 3275 3276 3277 3278 3279 3280
	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
Linus Torvalds 已提交
3281
	profile=	[KNL] Enable kernel profiling via /proc/profile
R
Randy Dunlap 已提交
3282 3283 3284 3285
			Format: [schedule,]<number>
			Param: "schedule" - profile schedule points.
			Param: <number> - step/bucket size as a power of 2 for
				statistical time based profiling.
3286 3287
			Param: "sleep" - profile D-state sleeping (millisecs).
				Requires CONFIG_SCHEDSTATS
3288
			Param: "kvm" - profile VM exits.
L
Linus Torvalds 已提交
3289 3290 3291

	prompt_ramdisk=	[RAM] List of RAM disks to prompt for floppy disk
			before loading.
3292
			See Documentation/blockdev/ramdisk.txt.
L
Linus Torvalds 已提交
3293

R
Randy Dunlap 已提交
3294 3295
	psmouse.proto=	[HW,MOUSE] Highest PS2 mouse protocol extension to
			probe for; one of (bare|imps|exps|lifebook|any).
L
Linus Torvalds 已提交
3296 3297
	psmouse.rate=	[HW,MOUSE] Set desired mouse report rate, in reports
			per second.
R
Randy Dunlap 已提交
3298 3299
	psmouse.resetafter=	[HW,MOUSE]
			Try to reset the device after so many bad packets
L
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3300 3301 3302 3303
			(0 = never).
	psmouse.resolution=
			[HW,MOUSE] Set desired mouse resolution, in dpi.
	psmouse.smartscroll=
R
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3304
			[HW,MOUSE] Controls Logitech smartscroll autorepeat.
L
Linus Torvalds 已提交
3305 3306
			0 = disabled, 1 = enabled (default).

3307 3308
	pstore.backend=	Specify the name of the pstore backend to use

L
Linus Torvalds 已提交
3309
	pt.		[PARIDE]
3310
			See Documentation/blockdev/paride.txt.
L
Linus Torvalds 已提交
3311

3312 3313 3314 3315
	pty.legacy_count=
			[KNL] Number of legacy pty's. Overwrites compiled-in
			default number.

3316
	quiet		[KNL] Disable most log messages
R
Randy Dunlap 已提交
3317

L
Linus Torvalds 已提交
3318 3319 3320 3321 3322 3323
	r128=		[HW,DRM]

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

	ramdisk_size=	[RAM] Sizes of RAM disks in kilobytes
3324
			See Documentation/blockdev/ramdisk.txt.
L
Linus Torvalds 已提交
3325

3326
	rcu_nocbs=	[KNL]
N
Noam Camus 已提交
3327 3328
			The argument is a cpu list, as described above.

P
Paul E. McKenney 已提交
3329 3330 3331
			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
3332 3333 3334 3335
			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
P
Paul E. McKenney 已提交
3336 3337 3338 3339
			offloaded CPUs, which can be useful for HPC and
			real-time workloads.  It can also improve energy
			efficiency for asymmetric multiprocessors.

3340
	rcu_nocb_poll	[KNL]
P
Paul E. McKenney 已提交
3341 3342 3343 3344 3345 3346 3347 3348 3349 3350
			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.

3351
	rcutree.blimit=	[KNL]
3352 3353
			Set maximum number of finished RCU callbacks to
			process in one batch.
D
Dipankar Sarma 已提交
3354

3355 3356 3357 3358 3359
	rcutree.dump_tree=	[KNL]
			Dump the structure of the rcu_node combining tree
			out at early boot.  This is used for diagnostic
			purposes, to verify correct tree setup.

3360 3361 3362 3363 3364
	rcutree.gp_cleanup_delay=	[KNL]
			Set the number of jiffies to delay each step of
			RCU grace-period cleanup.  This only has effect
			when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.

3365 3366 3367
	rcutree.gp_init_delay=	[KNL]
			Set the number of jiffies to delay each step of
			RCU grace-period initialization.  This only has
3368 3369 3370 3371 3372 3373 3374 3375 3376
			effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
			is set.

	rcutree.gp_preinit_delay=	[KNL]
			Set the number of jiffies to delay each step of
			RCU grace-period pre-initialization, that is,
			the propagation of recent CPU-hotplug changes up
			the rcu_node combining tree.  This only has effect
			when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3377

3378 3379 3380 3381 3382
	rcutree.rcu_fanout_exact= [KNL]
			Disable autobalancing of the rcu_node combining
			tree.  This is used by rcutorture, and might
			possibly be useful for architectures having high
			cache-to-cache transfer latencies.
3383

3384
	rcutree.rcu_fanout_leaf= [KNL]
3385 3386 3387 3388 3389 3390
			Change the number of CPUs assigned to each
			leaf rcu_node structure.  Useful for very
			large systems, which will choose the value 64,
			and for NUMA systems with large remote-access
			latencies, which will choose a value aligned
			with the appropriate hardware boundaries.
3391

3392 3393 3394 3395 3396 3397
	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().

3398
	rcutree.jiffies_till_first_fqs= [KNL]
3399 3400 3401 3402 3403
			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.

3404
	rcutree.jiffies_till_next_fqs= [KNL]
3405 3406 3407 3408
			Set delay between subsequent attempts to force
			quiescent states.  Units are jiffies, minimum
			value is one, and maximum value is HZ.

3409
	rcutree.kthread_prio= 	 [KNL,BOOT]
3410 3411 3412 3413 3414 3415 3416 3417 3418
			Set the SCHED_FIFO priority of the RCU per-CPU
			kthreads (rcuc/N). This value is also used for
			the priority of the RCU boost threads (rcub/N)
			and for the RCU grace-period kthreads (rcu_bh,
			rcu_preempt, and rcu_sched). If RCU_BOOST is
			set, valid values are 1-99 and the default is 1
			(the least-favored priority).  Otherwise, when
			RCU_BOOST is not set, valid values are 0-99 and
			the default is zero (non-realtime operation).
3419

3420 3421 3422 3423 3424 3425 3426
	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.

3427
	rcutree.qhimark= [KNL]
3428 3429
			Set threshold of queued RCU callbacks beyond which
			batch limiting is disabled.
D
Dipankar Sarma 已提交
3430

3431
	rcutree.qlowmark= [KNL]
3432 3433
			Set threshold of queued RCU callbacks below which
			batch limiting is re-enabled.
D
Dipankar Sarma 已提交
3434

3435
	rcutree.rcu_idle_gp_delay= [KNL]
3436 3437
			Set wakeup interval for idle CPUs that have
			RCU callbacks (RCU_FAST_NO_HZ=y).
3438

3439
	rcutree.rcu_idle_lazy_gp_delay= [KNL]
3440 3441 3442 3443
			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.
3444

3445 3446 3447 3448
	rcuperf.gp_exp= [KNL]
			Measure performance of expedited synchronous
			grace-period primitives.

3449 3450 3451 3452 3453 3454
	rcuperf.holdoff= [KNL]
			Set test-start holdoff period.  The purpose of
			this parameter is to delay the start of the
			test until boot completes in order to avoid
			interference.

3455 3456 3457 3458 3459 3460 3461 3462 3463 3464 3465 3466 3467 3468 3469 3470 3471 3472 3473 3474 3475 3476 3477 3478 3479 3480 3481 3482
	rcuperf.nreaders= [KNL]
			Set number of RCU readers.  The value -1 selects
			N, where N is the number of CPUs.  A value
			"n" less than -1 selects N-n+1, where N is again
			the number of CPUs.  For example, -2 selects N
			(the number of CPUs), -3 selects N+1, and so on.
			A value of "n" less than or equal to -N selects
			a single reader.

	rcuperf.nwriters= [KNL]
			Set number of RCU writers.  The values operate
			the same as for rcuperf.nreaders.
			N, where N is the number of CPUs

	rcuperf.perf_runnable= [BOOT]
			Start rcuperf running at boot time.

	rcuperf.shutdown= [KNL]
			Shut the system down after performance tests
			complete.  This is useful for hands-off automated
			testing.

	rcuperf.perf_type= [KNL]
			Specify the RCU implementation to test.

	rcuperf.verbose= [KNL]
			Enable additional printk() statements.

3483 3484 3485 3486 3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500
	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.

3501
	rcutorture.fqs_duration= [KNL]
3502 3503
			Set duration of force_quiescent_state bursts
			in microseconds.
3504

3505
	rcutorture.fqs_holdoff= [KNL]
3506 3507
			Set holdoff time within force_quiescent_state bursts
			in microseconds.
3508

3509
	rcutorture.fqs_stutter= [KNL]
3510 3511 3512 3513 3514 3515
			Set wait time between force_quiescent_state bursts
			in seconds.

	rcutorture.gp_cond= [KNL]
			Use conditional/asynchronous update-side
			primitives, if available.
3516

3517
	rcutorture.gp_exp= [KNL]
3518
			Use expedited update-side primitives, if available.
3519 3520

	rcutorture.gp_normal= [KNL]
3521 3522 3523 3524 3525 3526 3527 3528 3529 3530
			Use normal (non-expedited) asynchronous
			update-side primitives, if available.

	rcutorture.gp_sync= [KNL]
			Use normal (non-expedited) synchronous
			update-side primitives, if available.  If all
			of rcutorture.gp_cond=, rcutorture.gp_exp=,
			rcutorture.gp_normal=, and rcutorture.gp_sync=
			are zero, rcutorture acts as if is interpreted
			they are all non-zero.
3531

3532
	rcutorture.n_barrier_cbs= [KNL]
3533 3534
			Set callbacks/threads for rcu_barrier() testing.

3535
	rcutorture.nfakewriters= [KNL]
3536 3537 3538 3539
			Set number of concurrent RCU writers.  These just
			stress RCU, they don't participate in the actual
			test, hence the "fake".

3540
	rcutorture.nreaders= [KNL]
3541 3542 3543 3544 3545
			Set number of RCU readers.  The value -1 selects
			N-1, where N is the number of CPUs.  A value
			"n" less than -1 selects N-n-2, where N is again
			the number of CPUs.  For example, -2 selects N
			(the number of CPUs), -3 selects N+1, and so on.
3546

3547 3548 3549 3550
	rcutorture.object_debug= [KNL]
			Enable debug-object double-call_rcu() testing.

	rcutorture.onoff_holdoff= [KNL]
3551 3552
			Set time (s) after boot for CPU-hotplug testing.

3553
	rcutorture.onoff_interval= [KNL]
3554 3555 3556
			Set time (s) between CPU-hotplug operations, or
			zero to disable CPU-hotplug testing.

3557
	rcutorture.shuffle_interval= [KNL]
3558 3559 3560 3561
			Set task-shuffle interval (s).  Shuffling tasks
			allows some CPUs to go into dyntick-idle mode
			during the rcutorture test.

3562
	rcutorture.shutdown_secs= [KNL]
3563 3564 3565
			Set time (s) after boot system shutdown.  This
			is useful for hands-off automated testing.

3566
	rcutorture.stall_cpu= [KNL]
3567 3568 3569
			Duration of CPU stall (s) to test RCU CPU stall
			warnings, zero to disable.

3570
	rcutorture.stall_cpu_holdoff= [KNL]
3571 3572
			Time to wait (s) after boot before inducing stall.

3573
	rcutorture.stat_interval= [KNL]
3574 3575
			Time (s) between statistics printk()s.

3576
	rcutorture.stutter= [KNL]
3577 3578 3579 3580 3581
			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.

3582
	rcutorture.test_boost= [KNL]
3583 3584 3585 3586
			Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
			"Maybe" means test if the RCU implementation
			under test support RCU priority boosting.

3587
	rcutorture.test_boost_duration= [KNL]
3588 3589
			Duration (s) of each individual boost test.

3590
	rcutorture.test_boost_interval= [KNL]
3591 3592
			Interval (s) between each boost test.

3593
	rcutorture.test_no_idle_hz= [KNL]
3594 3595 3596
			Test RCU's dyntick-idle handling.  See also the
			rcutorture.shuffle_interval parameter.

3597 3598 3599
	rcutorture.torture_runnable= [BOOT]
			Start rcutorture running at boot time.

3600
	rcutorture.torture_type= [KNL]
3601 3602
			Specify the RCU implementation to test.

3603
	rcutorture.verbose= [KNL]
3604 3605
			Enable additional printk() statements.

3606 3607 3608 3609 3610 3611
	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.

3612 3613 3614 3615 3616 3617
	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.
3618
			No effect on CONFIG_TINY_RCU kernels.
3619

3620 3621 3622 3623
	rcupdate.rcu_normal= [KNL]
			Use only normal grace-period primitives,
			for example, synchronize_rcu() instead of
			synchronize_rcu_expedited().  This improves
3624 3625 3626 3627 3628
			real-time latency, CPU utilization, and
			energy efficiency, but can expose users to
			increased grace-period latency.  This parameter
			overrides rcupdate.rcu_expedited.  No effect on
			CONFIG_TINY_RCU kernels.
3629

3630 3631 3632
	rcupdate.rcu_normal_after_boot= [KNL]
			Once boot has completed (that is, after
			rcu_end_inkernel_boot() has been invoked), use
3633 3634
			only normal grace-period primitives.  No effect
			on CONFIG_TINY_RCU kernels.
3635

3636 3637 3638 3639 3640
	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.

3641 3642 3643 3644 3645 3646 3647 3648 3649
	rcupdate.rcu_self_test= [KNL]
			Run the RCU early boot self tests

	rcupdate.rcu_self_test_bh= [KNL]
			Run the RCU bh early boot self tests

	rcupdate.rcu_self_test_sched= [KNL]
			Run the RCU sched early boot self tests

3650 3651 3652 3653 3654
	rdinit=		[KNL]
			Format: <full_path>
			Run specified binary instead of /init from the ramdisk,
			used for early userspace startup. See initrd.

3655 3656 3657 3658 3659 3660 3661 3662 3663 3664 3665
	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
3666

3667 3668
	relax_domain_level=
			[KNL, SMP] Set scheduler's default relax_domain_level.
3669
			See Documentation/cgroup-v1/cpusets.txt.
3670

3671 3672 3673 3674 3675 3676 3677
	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
3678 3679
	reserve=	[KNL,BUGS] Force the kernel to ignore some iomem area

3680
	reservetop=	[X86-32]
3681 3682 3683 3684
			Format: nn[KMG]
			Reserves a hole at the top of the kernel virtual
			address space.

3685 3686 3687 3688 3689
	reservelow=	[X86]
			Format: nn[K]
			Set the amount of memory to reserve for BIOS at
			the bottom of the address space.

3690 3691 3692
	reset_devices	[KNL] Force drivers to reset the underlying device
			during initialization.

R
Randy Dunlap 已提交
3693 3694
	resume=		[SWSUSP]
			Specify the partition device for software suspend
3695 3696
			Format:
			{/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
L
Linus Torvalds 已提交
3697

3698 3699 3700 3701 3702 3703
	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

3704 3705 3706
	resumedelay=	[HIBERNATION] Delay (in seconds) to pause before attempting to
			read the resume files

3707 3708 3709 3710
	resumewait	[HIBERNATION] Wait (indefinitely) for resume device to show up.
			Useful for devices that are detected asynchronously
			(e.g. USB and MMC devices).

3711 3712 3713 3714
	hibernate=	[HIBERNATION]
		noresume	Don't check if there's a hibernation image
				present during boot.
		nocompress	Don't compress/decompress hibernation images.
3715
		no		Disable hibernation and resume.
3716 3717 3718
		protect_image	Turn on image protection during restoration
				(that will set all pages holding image data
				during restoration read-only).
3719

3720 3721
	retain_initrd	[RAM] Keep initrd memory after extraction

3722 3723 3724 3725 3726 3727 3728 3729 3730 3731 3732 3733
	rfkill.default_state=
		0	"airplane mode".  All wifi, bluetooth, wimax, gps, fm,
			etc. communication is blocked by default.
		1	Unblocked.

	rfkill.master_switch_mode=
		0	The "airplane mode" button does nothing.
		1	The "airplane mode" button toggles between everything
			blocked and the previous configuration.
		2	The "airplane mode" button toggles between everything
			blocked and everything unblocked.

L
Linus Torvalds 已提交
3734 3735 3736 3737 3738
	rhash_entries=	[KNL,NET]
			Set number of hash buckets for route cache

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

3739 3740 3741 3742
	rodata=		[KNL]
		on	Mark read-only kernel memory as read-only (default).
		off	Leave read-only kernel memory writable for debugging.

3743 3744 3745 3746 3747 3748
	rockchip.usb_uart
			Enable the uart passthrough on the designated usb port
			on Rockchip SoCs. When active, the signals of the
			debug-uart get routed to the D+ and D- pins of the usb
			port and the regular usb controller gets disabled.

L
Linus Torvalds 已提交
3749
	root=		[KNL] Root filesystem
3750
			See name_to_dev_t comment in init/do_mounts.c.
L
Linus Torvalds 已提交
3751 3752 3753 3754 3755 3756 3757 3758

	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

3759 3760 3761 3762
	rootwait	[KNL] Wait (indefinitely) for root device to show up.
			Useful for devices that are detected asynchronously
			(e.g. USB and MMC devices).

3763 3764 3765 3766 3767
	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
3768 3769 3770 3771
	rw		[KNL] Mount root device read-write on boot

	S		[KNL] Run init in single mode

3772 3773 3774 3775 3776 3777 3778
	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
3779 3780 3781 3782
	sa1100ir	[NET]
			See drivers/net/irda/sa1100_ir.c.

	sbni=		[NET] Granch SBNI12 leased line adapter
R
Randy Dunlap 已提交
3783

3784 3785
	sched_debug	[KNL] Enables verbose scheduler debug messages.

3786 3787 3788 3789
	schedstats=	[KNL,X86] Enable or disable scheduled statistics.
			Allowed values are enable and disable. This feature
			incurs a small amount of overhead in the scheduler
			but is useful for debugging and performance tuning.
3790

M
Mike Galbraith 已提交
3791 3792 3793 3794 3795 3796 3797 3798 3799
	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.

3800 3801 3802 3803 3804 3805 3806
	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
3807 3808 3809 3810 3811 3812 3813 3814
			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.

3815 3816 3817 3818 3819 3820 3821
	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.

3822
	serialnumber	[BUGS=X86-32]
L
Linus Torvalds 已提交
3823 3824 3825

	shapers=	[NET]
			Maximal number of shapers.
R
Randy Dunlap 已提交
3826

L
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3827 3828
	simeth=		[IA-64]
	simscsi=
R
Randy Dunlap 已提交
3829

L
Linus Torvalds 已提交
3830 3831
	slram=		[HW,MTD]

3832 3833 3834 3835 3836 3837 3838
	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.

3839 3840 3841 3842 3843 3844
	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.

3845 3846 3847 3848 3849 3850 3851
	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
3852 3853

	slub_max_order= [MM, SLUB]
3854 3855 3856 3857
			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
3858 3859

	slub_min_objects=	[MM, SLUB]
3860 3861 3862 3863 3864 3865
			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
3866 3867 3868
			For more information see Documentation/vm/slub.txt.

	slub_min_order=	[MM, SLUB]
3869
			Determines the minimum page order for slabs. Must be
3870
			lower than slub_max_order.
C
Christoph Lameter 已提交
3871 3872 3873
			For more information see Documentation/vm/slub.txt.

	slub_nomerge	[MM, SLUB]
3874 3875
			Same with slab_nomerge. This is supported for legacy.
			See slab_nomerge for more information.
C
Christoph Lameter 已提交
3876

L
Linus Torvalds 已提交
3877 3878 3879
	smart2=		[HW]
			Format: <io1>[,<io2>[,...,<io8>]]

B
Bjorn Helgaas 已提交
3880 3881 3882 3883 3884 3885 3886 3887 3888 3889 3890
	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

3891 3892 3893 3894 3895 3896 3897
	smt		[KNL,S390] Set the maximum number of threads (logical
			CPUs) to use per physical CPU on systems capable of
			symmetric multithreading (SMT). Will be capped to the
			actual hardware limit.
			Format: <integer>
			Default: -1 (no limit)

I
Ingo Molnar 已提交
3898 3899
	softlockup_panic=
			[KNL] Should the soft-lockup detector generate panics.
3900
			Format: <integer>
I
Ingo Molnar 已提交
3901

3902 3903 3904 3905 3906
	softlockup_all_cpu_backtrace=
			[KNL] Should the soft-lockup detector generate
			backtraces on all cpus.
			Format: <integer>

L
Linus Torvalds 已提交
3907
	sonypi.*=	[HW] Sony Programmable I/O Control Device driver
P
Paul Bolle 已提交
3908
			See Documentation/laptops/sonypi.txt
L
Linus Torvalds 已提交
3909 3910 3911 3912 3913 3914

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

3915 3916 3917
	stacktrace	[FTRACE]
			Enabled the stack tracer on boot up.

3918 3919 3920 3921 3922 3923 3924 3925
	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
3926 3927 3928 3929 3930 3931 3932 3933 3934 3935 3936 3937 3938
	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>...]]

3939 3940 3941 3942 3943 3944 3945 3946 3947 3948 3949 3950
	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.

3951 3952 3953 3954 3955 3956
	sunrpc.svc_rpc_per_connection_limit=
			[NFS,SUNRPC]
			Limit the number of requests that the server will
			process in parallel from a single connection.
			The default value is 0 (no limit).

3957 3958 3959 3960 3961 3962 3963 3964 3965 3966 3967 3968 3969 3970 3971 3972
	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)

3973 3974 3975 3976 3977 3978 3979 3980 3981
	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.

3982 3983 3984 3985 3986 3987 3988
	suspend.pm_test_delay=
			[SUSPEND]
			Sets the number of seconds to remain in a suspend test
			mode before resuming the system (see
			/sys/power/pm_test). Only available when CONFIG_PM_DEBUG
			is set. Default value is 5.

3989
	swapaccount=[0|1]
3990 3991
			[KNL] Enable accounting of swap in memory resource
			controller if no parameter or 1 is given or disable
3992
			it if 0 is given (See Documentation/cgroup-v1/memory.txt)
3993

J
Jiri Kosina 已提交
3994 3995 3996 3997 3998
	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
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L
Linus Torvalds 已提交
4000 4001
	switches=	[HW,M68k]

4002 4003 4004 4005 4006 4007 4008 4009 4010
	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.

4011 4012 4013 4014 4015 4016
	sysrq_always_enabled
			[KNL]
			Ignore sysrq setting - this boot parameter will
			neutralize any effect of /proc/sys/kernel/sysrq.
			Useful for debugging.

4017 4018 4019 4020 4021 4022 4023
	tcpmhash_entries= [KNL,NET]
			Set the number of tcp_metrics_hash slots.
			Default value is 8192 or 16384 depending on total
			ram pages. This is used to specify the TCP metrics
			cache size. See Documentation/networking/ip-sysctl.txt
			"tcp_no_metrics_save" section for more details.

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Linus Torvalds 已提交
4024 4025
	tdfx=		[HW,DRM]

4026
	test_suspend=	[SUSPEND][,N]
D
David Brownell 已提交
4027
			Specify "mem" (for Suspend-to-RAM) or "standby" (for
4028 4029 4030 4031 4032
			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
4033

L
Linus Torvalds 已提交
4034 4035 4036
	thash_entries=	[KNL,NET]
			Set number of hash buckets for TCP connection

4037 4038 4039 4040
	thermal.act=	[HW,ACPI]
			-1: disable all active trip points in all thermal zones
			<degrees C>: override all lowest active trip points

4041 4042
	thermal.crt=	[HW,ACPI]
			-1: disable all critical trip points in all thermal zones
4043
			<degrees C>: override all critical trip points
4044

4045 4046 4047 4048
	thermal.nocrt=	[HW,ACPI]
			Set to disable actions on ACPI thermal zone
			critical and hot trip points.

4049 4050 4051
	thermal.off=	[HW,ACPI]
			1: disable ACPI thermal control

4052 4053
	thermal.psv=	[HW,ACPI]
			-1: disable all passive trip points
4054 4055
			<degrees C>: override all passive trip points to this
			value
4056

4057 4058 4059 4060 4061
	thermal.tzp=	[HW,ACPI]
			Specify global default ACPI thermal zone polling rate
			<deci-seconds>: poll all this frequency
			0: no polling (default)

4062 4063
	threadirqs	[KNL]
			Force threading of all interrupt handlers except those
4064
			marked explicitly IRQF_NO_THREAD.
4065

4066 4067 4068 4069 4070 4071 4072 4073 4074
	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
4075 4076
			API to send swap pages to the hypervisor. If disabled
			the selfballooning and selfshrinking are force disabled.
4077 4078 4079 4080 4081 4082 4083 4084 4085 4086

	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.

4087 4088 4089
	topology=	[S390]
			Format: {off | on}
			Specify if the kernel should make use of the cpu
4090 4091
			topology information if the hardware supports this.
			The scheduler will make use of this information and
4092
			e.g. base its process migration decisions on it.
H
Heiko Carstens 已提交
4093
			Default is on.
4094

4095 4096 4097 4098 4099 4100
	topology_updates= [KNL, PPC, NUMA]
			Format: {off}
			Specify if the kernel should ignore (off)
			topology updates sent by the hypervisor to this
			LPAR.

L
Linus Torvalds 已提交
4101 4102
	tp720=		[HW,PS2]

4103 4104 4105 4106 4107 4108 4109 4110 4111
	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.

4112
	trace_buf_size=nn[KMG]
4113
			[FTRACE] will set tracing buffer size on each cpu.
4114

4115 4116
	trace_event=[event-list]
			[FTRACE] Set and start specified trace events in order
4117 4118 4119
			to facilitate early boot debugging. The event-list is a
			comma separated list of trace events to enable. See
			also Documentation/trace/events.txt
4120

4121 4122 4123 4124 4125 4126 4127 4128 4129 4130 4131 4132 4133 4134 4135 4136
	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.

4137 4138 4139 4140 4141 4142 4143 4144 4145 4146 4147 4148 4149 4150 4151 4152 4153 4154
	tp_printk[FTRACE]
			Have the tracepoints sent to printk as well as the
			tracing ring buffer. This is useful for early boot up
			where the system hangs or reboots and does not give the
			option for reading the tracing buffer or performing a
			ftrace_dump_on_oops.

			To turn off having tracepoints sent to printk,
			 echo 0 > /proc/sys/kernel/tracepoint_printk
			Note, echoing 1 into this file without the
			tracepoint_printk kernel cmdline option has no effect.

			** CAUTION **

			Having tracepoints sent to printk() and activating high
			frequency tracepoints such as irq or sched, can cause
			the system to live lock.

4155 4156 4157 4158 4159 4160 4161 4162 4163 4164 4165 4166 4167
	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

4168 4169 4170 4171 4172 4173 4174
	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.

4175
	tsc=		Disable clocksource stability checks for TSC.
4176 4177
			Format: <string>
			[x86] reliable: mark tsc clocksource as reliable, this
4178 4179 4180 4181
			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
4182 4183 4184 4185
			[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.
4186

R
Randy Dunlap 已提交
4187 4188 4189 4190
	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
4191 4192
			See also Documentation/input/joystick-parport.txt

C
Christian Kujau 已提交
4193 4194 4195 4196 4197
	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.

4198 4199 4200
	uhash_entries=	[KNL,NET]
			Set number of hash buckets for UDP/UDP-Lite connections

4201 4202 4203 4204 4205 4206 4207 4208
	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.

4209
	unknown_nmi_panic
4210
			[X86] Cause panic on unknown NMI.
4211

4212 4213 4214 4215 4216
	usbcore.authorized_default=
			[USB] Default USB device authorization:
			(default -1 = authorized except for wireless USB,
			0 = not authorized, 1 = authorized)

4217 4218 4219 4220 4221
	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
4222
			to a negative value won't be autosuspended at all.
4223

4224 4225 4226
	usbcore.usbfs_snoop=
			[USB] Set to log all usbfs traffic (default 0 = off).

4227 4228 4229 4230
	usbcore.usbfs_snoop_max=
			[USB] Maximum number of bytes to snoop in each URB
			(default = 65536).

4231 4232 4233 4234 4235 4236 4237
	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).

4238 4239 4240 4241
	usbcore.usbfs_memory_mb=
			[USB] Memory limit (in MB) for buffers allocated by
			usbfs (default = 16, 0 = max = 2047).

4242 4243 4244 4245 4246 4247 4248 4249 4250
	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).

4251 4252
	usbcore.nousb	[USB] Disable the USB subsystem

L
Linus Torvalds 已提交
4253 4254
	usbhid.mousepoll=
			[USBHID] The interval which mice are to be polled at.
R
Randy Dunlap 已提交
4255

4256 4257
	usb-storage.delay_use=
			[UMS] The delay in seconds before a new device is
4258
			scanned for Logical Units (default 1).
4259 4260 4261 4262 4263 4264 4265 4266 4267

	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:
4268 4269
				a = SANE_SENSE (collect more than 18 bytes
					of sense data);
A
Alan Stern 已提交
4270 4271
				b = BAD_SENSE (don't collect more than 18
					bytes of sense data);
4272 4273
				c = FIX_CAPACITY (decrease the reported
					device capacity by one sector);
4274 4275 4276 4277
				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
4278 4279
				f = NO_REPORT_OPCODES (don't use report opcodes
					command, uas only);
4280 4281
				g = MAX_SECTORS_240 (don't transfer more than
					240 sectors at a time, uas only);
4282 4283 4284
				h = CAPACITY_HEURISTICS (decrease the
					reported device capacity by one
					sector if the number is odd);
4285 4286
				i = IGNORE_DEVICE (don't bind to this
					device);
4287 4288
				j = NO_REPORT_LUNS (don't use report luns
					command, uas only);
4289 4290 4291 4292
				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);
A
Alan Stern 已提交
4293 4294
				n = INITIAL_READ10 (force a retry of the
					initial READ(10) command);
4295 4296
				o = CAPACITY_OK (accept the capacity
					reported by the device);
4297 4298
				p = WRITE_CACHE (the device cache is ON
					by default);
4299 4300 4301 4302
				r = IGNORE_RESIDUE (the device reports
					bogus residue values);
				s = SINGLE_LUN (the device has only one
					Logical Unit);
4303 4304
				t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
					commands, uas only);
4305
				u = IGNORE_UAS (don't bind to the uas driver);
4306 4307
				w = NO_WP_DETECT (don't test whether the
					medium is write-protected).
4308 4309
				y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
					even if the device claims no cache)
4310 4311
			Example: quirks=0419:aaf5:rl,0421:0433:rc

4312 4313 4314 4315 4316 4317 4318 4319 4320 4321
	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

4322 4323 4324 4325 4326 4327 4328
	userpte=
			[X86] Flags controlling user PTE allocations.

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

4329
	vdso=		[X86,SH]
4330 4331 4332
			On X86_32, this is an alias for vdso32=.  Otherwise:

			vdso=1: enable VDSO (the default)
4333 4334
			vdso=0: disable VDSO mapping

4335 4336 4337 4338 4339 4340 4341 4342 4343 4344 4345 4346 4347
	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
4348

4349 4350 4351
	vector=		[IA-64,SMP]
			vector=percpu: enable percpu vector domain

L
Linus Torvalds 已提交
4352 4353 4354
	video=		[FB] Frame buffer configuration
			See Documentation/fb/modedb.txt.

4355 4356 4357 4358 4359 4360 4361
	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.
4362
			default: 1
4363

4364 4365 4366 4367 4368 4369 4370 4371 4372 4373 4374 4375 4376 4377 4378 4379
	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.

4380
	vga=		[BOOT,X86-32] Select a particular video mode
4381
			See Documentation/x86/boot.txt and
R
Randy Dunlap 已提交
4382
			Documentation/svga.txt.
L
Linus Torvalds 已提交
4383 4384 4385 4386
			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
4387
	vmalloc=nn[KMG]	[KNL,BOOT] Forces the vmalloc area to have an exact
L
Linus Torvalds 已提交
4388 4389 4390 4391 4392
			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.

4393 4394
	vmhalt=		[KNL,S390] Perform z/VM CP command after system halt.
			Format: <command>
L
Linus Torvalds 已提交
4395

4396 4397 4398 4399 4400
	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
4401

4402 4403 4404 4405 4406 4407 4408 4409
	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
4410 4411
			emulate     [default] Vsyscalls turn into traps and are
			            emulated reasonably safely.
4412

A
Andy Lutomirski 已提交
4413
			native      Vsyscalls are native syscall instructions.
4414 4415 4416 4417 4418 4419 4420 4421 4422
			            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.

4423 4424 4425 4426
	vt.color=	[VT] Default text color.
			Format: 0xYX, X = foreground, Y = background.
			Default: 0x07 = light gray on black.

4427 4428 4429 4430 4431
	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.

4432 4433 4434 4435 4436 4437 4438 4439 4440 4441 4442 4443 4444 4445 4446 4447 4448 4449 4450 4451 4452 4453 4454 4455 4456
	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.

4457 4458 4459 4460 4461 4462 4463 4464 4465
	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.

4466 4467 4468 4469 4470 4471
	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.

4472 4473 4474 4475
	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
4476

T
Tejun Heo 已提交
4477 4478 4479 4480 4481 4482 4483 4484 4485
	workqueue.watchdog_thresh=
			If CONFIG_WQ_WATCHDOG is configured, workqueue can
			warn stall conditions and dump internal state to
			help debugging.  0 disables workqueue stall
			detection; otherwise, it's the stall threshold
			duration in seconds.  The default value is 30 and
			it can be updated at runtime by writing to the
			corresponding sysfs file.

4486 4487 4488 4489 4490 4491 4492 4493 4494
	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/.

4495 4496 4497 4498 4499 4500 4501 4502 4503 4504 4505 4506 4507 4508 4509
	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.

4510 4511 4512 4513 4514 4515 4516 4517 4518 4519 4520
	workqueue.debug_force_rr_cpu
			Workqueue used to implicitly guarantee that work
			items queued without explicit CPU specified are put
			on the local CPU.  This guarantee is no longer true
			and while local CPU is still preferred work items
			may be put on foreign CPUs.  This debug option
			forces round-robin CPU selection to flush out
			usages which depend on the now broken guarantee.
			When enabled, memory and cache locality will be
			impacted.

4521 4522 4523 4524
	x2apic_phys	[X86-64,APIC] Use x2apic physical mode instead of
			default x2apic cluster mode on platforms
			supporting x2apic.

4525 4526
	x86_intel_mid_timer= [X86-32,APBT]
			Choose timer option for x86 Intel MID platform.
4527 4528
			Two valid options are apbt timer only and lapic timer
			plus one apbt timer for broadcast timer.
4529
			x86_intel_mid_timer=apbt_only | lapic_and_apbt
4530

4531 4532 4533 4534 4535 4536 4537
	xen_512gb_limit		[KNL,X86-64,XEN]
			Restricts the kernel running paravirtualized under Xen
			to use only up to 512 GB of RAM. The reason to do so is
			crash analysis tools and Xen tools for doing domain
			save/restore/migration must be enabled to handle larger
			domains.

4538 4539 4540 4541 4542 4543 4544
	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)
4545 4546 4547
			unnecessary -- unplugging emulated devices is
				unnecessary even if the host did not respond to
				the unplug protocol
4548
			never -- do not unplug even if version check succeeds
4549

4550 4551 4552 4553
	xen_nopvspin	[X86,XEN]
			Disables the ticketlock slowpath using Xen PV
			optimizations.

4554 4555 4556 4557
	xen_nopv	[X86]
			Disables the PV optimizations forcing the HVM guest to
			run as generic HVM guest with no PV drivers.

L
Linus Torvalds 已提交
4558
	xirc2ps_cs=	[NET,PCMCIA]
R
Randy Dunlap 已提交
4559 4560
			Format:
			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
L
Linus Torvalds 已提交
4561

R
Randy Dunlap 已提交
4562
______________________________________________________________________
L
Linus Torvalds 已提交
4563 4564 4565 4566

TODO:

	Add more DRM drivers.