kernel-parameters.txt 207 KB
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	acpi=		[HW,ACPI,X86,ARM64]
			Advanced Configuration and Power Interface
			Format: { force | on | off | strict | noirq | rsdt |
				  copy_dsdt }
			force -- enable ACPI if default was off
			on -- enable ACPI but allow fallback to DT [arm64]
			off -- disable ACPI if default was on
			noirq -- do not use ACPI for IRQ routing
			strict -- Be less tolerant of platforms that are not
				strictly ACPI specification compliant.
			rsdt -- prefer RSDT over (default) XSDT
			copy_dsdt -- copy DSDT to memory
			For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
			are available

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			See also Documentation/power/runtime_pm.rst, 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
			default: 0

	acpi_backlight=	[HW,ACPI]
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			{ vendor | video | native | none }
			If set to vendor, prefer vendor-specific driver
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			(e.g. thinkpad_acpi, sony_acpi, etc.) instead
			of the ACPI video.ko driver.
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			If set to video, use the ACPI video.ko driver.
			If set to native, use the device's native backlight mode.
			If set to none, disable the ACPI backlight interface.
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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.

	acpica_no_return_repair [HW, ACPI]
			Disable AML predefined validation mechanism
			This mechanism can repair the evaluation result to make
			the return objects more ACPI specification compliant.
			This option is useful for developers to identify the
			root cause of an AML interpreter issue when the issue
			has something to do with the repair mechanism.

	acpi.debug_layer=	[HW,ACPI,ACPI_DEBUG]
	acpi.debug_level=	[HW,ACPI,ACPI_DEBUG]
			Format: <int>
			CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
			debug output.  Bits in debug_layer correspond to a
			_COMPONENT in an ACPI source file, e.g.,
			    #define _COMPONENT ACPI_PCI_COMPONENT
			Bits in debug_level correspond to a level in
			ACPI_DEBUG_PRINT statements, e.g.,
			    ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
			The debug_level mask defaults to "info".  See
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			Documentation/firmware-guide/acpi/debug.rst for more information about
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			debug layers and levels.

			Enable processor driver info messages:
			    acpi.debug_layer=0x20000000
			Enable PCI/PCI interrupt routing info messages:
			    acpi.debug_layer=0x400000
			Enable AML "Debug" output, i.e., stores to the Debug
			object while interpreting AML:
			    acpi.debug_layer=0xffffffff acpi.debug_level=0x2
			Enable all messages related to ACPI hardware:
			    acpi.debug_layer=0x2 acpi.debug_level=0xffffffff

			Some values produce so much output that the system is
			unusable.  The "log_buf_len" parameter may be useful
			if you need to capture more output.

	acpi_enforce_resources=	[ACPI]
			{ strict | lax | no }
			Check for resource conflicts between native drivers
			and ACPI OperationRegions (SystemIO and SystemMemory
			only). IO ports and memory declared in ACPI might be
			used by the ACPI subsystem in arbitrary AML code and
			can interfere with legacy drivers.
			strict (default): access to resources claimed by ACPI
			is denied; legacy drivers trying to access reserved
			resources will fail to bind to device using them.
			lax: access to resources claimed by ACPI is allowed;
			legacy drivers trying to access reserved resources
			will bind successfully but a warning message is logged.
			no: ACPI OperationRegions are not marked as reserved,
			no further checks are performed.

	acpi_force_table_verification	[HW,ACPI]
			Enable table checksum verification during early stage.
			By default, this is disabled due to x86 early mapping
			size limitation.

	acpi_irq_balance [HW,ACPI]
			ACPI will balance active IRQs
			default in APIC mode

	acpi_irq_nobalance [HW,ACPI]
			ACPI will not move active IRQs (default)
			default in PIC mode

	acpi_irq_isa=	[HW,ACPI] If irq_balance, mark listed IRQs used by ISA
			Format: <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_mask_gpe=	[HW,ACPI]
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			Due to the existence of _Lxx/_Exx, some GPEs triggered
			by unsupported hardware/firmware features can result in
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			GPE floodings that cannot be automatically disabled by
			the GPE dispatcher.
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			This facility can be used to prevent such uncontrolled
			GPE floodings.
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			Format: <byte>
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	acpi_no_auto_serialize	[HW,ACPI]
			Disable auto-serialization of AML methods
			AML control methods that contain the opcodes to create
			named objects will be marked as "Serialized" by the
			auto-serialization feature.
			This feature is enabled by default.
			This option allows to turn off the feature.

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

	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_no_watchdog	[HW,ACPI,WDT]
			Ignore the ACPI-based watchdog interface (WDAT) and let
			a native driver control the watchdog device instead.

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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.

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

	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).

	acpi_osi=	[HW,ACPI] Modify list of supported OS interface strings
			acpi_osi="string1"	# add string1
			acpi_osi="!string2"	# remove string2
			acpi_osi=!*		# remove all strings
			acpi_osi=!		# disable all built-in OS vendor
						  strings
			acpi_osi=!!		# enable all built-in OS vendor
						  strings
			acpi_osi=		# disable all strings

			'acpi_osi=!' can be used in combination with single or
			multiple 'acpi_osi="string1"' to support specific OS
			vendor string(s).  Note that such command can only
			affect the default state of the OS vendor strings, thus
			it cannot affect the default state of the feature group
			strings and the current state of the OS vendor strings,
			specifying it multiple times through kernel command line
			is meaningless.  This command is useful when one do not
			care about the state of the feature group strings which
			should be controlled by the OSPM.
			Examples:
			  1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
			     to 'acpi_osi="Windows 2000" acpi_osi=!', they all
			     can make '_OSI("Windows 2000")' TRUE.

			'acpi_osi=' cannot be used in combination with other
			'acpi_osi=' command lines, the _OSI method will not
			exist in the ACPI namespace.  NOTE that such command can
			only affect the _OSI support state, thus specifying it
			multiple times through kernel command line is also
			meaningless.
			Examples:
			  1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
			     FALSE.

			'acpi_osi=!*' can be used in combination with single or
			multiple 'acpi_osi="string1"' to support specific
			string(s).  Note that such command can affect the
			current state of both the OS vendor strings and the
			feature group strings, thus specifying it multiple times
			through kernel command line is meaningful.  But it may
			still not able to affect the final state of a string if
			there are quirks related to this string.  This command
			is useful when one want to control the state of the
			feature group strings to debug BIOS issues related to
			the OSPM features.
			Examples:
			  1. 'acpi_osi="Module Device" acpi_osi=!*' can make
			     '_OSI("Module Device")' FALSE.
			  2. 'acpi_osi=!* acpi_osi="Module Device"' can make
			     '_OSI("Module Device")' TRUE.
			  3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
			     equivalent to
			     'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
			     and
			     'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
			     they all will make '_OSI("Windows 2000")' TRUE.

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

	acpi_sci=	[HW,ACPI] ACPI System Control Interrupt trigger mode
			Format: { level | edge | high | low }

	acpi_skip_timer_override [HW,ACPI]
			Recognize and ignore IRQ0/pin2 Interrupt Override.
			For broken nForce2 BIOS resulting in XT-PIC timer.

	acpi_sleep=	[HW,ACPI] Sleep options
			Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
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				  old_ordering, nonvs, sci_force_enable, nobl }
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			See Documentation/power/video.rst for information on
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			s3_bios and s3_mode.
			s3_beep is for debugging; it makes the PC's speaker beep
			as soon as the kernel's real-mode entry point is called.
			s4_nohwsig prevents ACPI hardware signature from being
			used during resume from hibernation.
			old_ordering causes the ACPI 1.0 ordering of the _PTS
			control method, with respect to putting devices into
			low power states, to be enforced (the ACPI 2.0 ordering
			of _PTS is used by default).
			nonvs prevents the kernel from saving/restoring the
			ACPI NVS memory during suspend/hibernation and resume.
			sci_force_enable causes the kernel to set SCI_EN directly
			on resume from S1/S3 (which is against the ACPI spec,
			but some broken systems don't work without it).
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			nobl causes the internal blacklist of systems known to
			behave incorrectly in some ways with respect to system
			suspend and resume to be ignored (use wisely).
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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.

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

	ALSA		[HW,ALSA]
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			See Documentation/sound/alsa-configuration.rst
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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.

	align_va_addr=	[X86-64]
			Align virtual addresses by clearing slice [14:12] when
			allocating a VMA at process creation time. This option
			gives you up to 3% performance improvement on AMD F15h
			machines (where it is enabled by default) for a
			CPU-intensive style benchmark, and it can vary highly in
			a microbenchmark depending on workload and compiler.

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

	alloc_snapshot	[FTRACE]
			Allocate the ftrace snapshot buffer on boot up when the
			main buffer is allocated. This is handy if debugging
			and you need to use tracing_snapshot() on boot up, and
			do not want to use tracing_snapshot_alloc() as it needs
			to be done where GFP_KERNEL allocations are allowed.

	amd_iommu=	[HW,X86-64]
			Pass parameters to the AMD IOMMU driver in the system.
			Possible values are:
			fullflush - enable flushing of IO/TLB entries when
				    they are unmapped. Otherwise they are
				    flushed before they will be reused, which
				    is a lot of faster
			off	  - do not initialize any AMD IOMMU found in
				    the system
			force_isolation - Force device isolation for all
					  devices. The IOMMU driver is not
					  allowed anymore to lift isolation
					  requirements as needed. This option
					  does not override iommu=pt

	amd_iommu_dump=	[HW,X86-64]
			Enable AMD IOMMU driver option to dump the ACPI table
			for AMD IOMMU. With this option enabled, AMD IOMMU
			driver will print ACPI tables for AMD IOMMU during
			IOMMU initialization.

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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/joydev/joystick.rst
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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>

	apc=		[HW,SPARC]
			Power management functions (SPARCstation-4/5 + deriv.)
			Format: noidle
			Disable APC CPU standby support. SPARCstation-Fox does
			not play well with APC CPU idle - disable it if you have
			APC and your system crashes randomly.

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	apic=		[APIC,X86] Advanced Programmable Interrupt Controller
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			Change the output verbosity while 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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			For X86-32, this can also be used to specify an APIC
			driver name.
			Format: apic=driver_name
			Examples: apic=bigsmp
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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

	autoconf=	[IPV6]
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			See Documentation/networking/ipv6.rst.
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	show_lapic=	[APIC,X86] Advanced Programmable Interrupt Controller
			Limit apic dumping. The parameter defines the maximal
			number of local apics being dumped. Also it is possible
			to set it to "all" by meaning -- no limit here.
			Format: { 1 (default) | 2 | ... | all }.
			The parameter valid if only apic=debug or
			apic=verbose is specified.
			Example: apic=debug show_lapic=all

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

	arcrimi=	[HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
			Format: <io>,<irq>,<nodeID>

	ataflop=	[HW,M68k]

	atarimouse=	[HW,MOUSE] Atari Mouse

	atkbd.extra=	[HW] Enable extra LEDs and keys on IBM RapidAccess,
			EzKey and similar keyboards

	atkbd.reset=	[HW] Reset keyboard during initialization

	atkbd.set=	[HW] Select keyboard code set
			Format: <int> (2 = AT (default), 3 = PS/2)

	atkbd.scroll=	[HW] Enable scroll wheel on MS Office and similar
			keyboards

	atkbd.softraw=	[HW] Choose between synthetic and real raw mode
			Format: <bool> (0 = real, 1 = synthetic (default))

	atkbd.softrepeat= [HW]
			Use software keyboard repeat

	audit=		[KNL] Enable the audit sub-system
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			Format: { "0" | "1" | "off" | "on" }
			0 | off - kernel audit is disabled and can not be
			    enabled until the next reboot
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			unset - kernel audit is initialized but disabled and
			    will be fully enabled by the userspace auditd.
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			1 | on - 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

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

	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.

	baycom_epp=	[HW,AX25]
			Format: <io>,<mode>

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

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

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

	blkdevparts=	Manual partition parsing of block device(s) for
			embedded devices based on command line input.
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			See Documentation/block/cmdline-partition.rst
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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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	bootconfig	[KNL]
			Extended command line options can be added to an initrd
			and this will cause the kernel to look for it.

			See Documentation/admin-guide/bootconfig.rst

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

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	bgrt_disable	[ACPI][X86]
			Disable BGRT to avoid flickering OEM logo.

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	bttv.card=	[HW,V4L] bttv (bt848 + bt878 based grabber cards)
	bttv.radio=	Most important insmod options are available as
			kernel args too.
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	bttv.pll=	See Documentation/admin-guide/media/bttv.rst
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	bttv.tuner=

	bulk_remove=off	[PPC]  This parameter disables the use of the pSeries
			firmware feature for flushing multiple hpte entries
			at a time.

	c101=		[NET] Moxa C101 synchronous serial card

	cachesize=	[BUGS=X86-32] Override level 2 CPU cache size detection.
			Sometimes CPU hardware bugs make them report the cache
			size incorrectly. The kernel will attempt work arounds
			to fix known problems, but for some CPUs it is not
			possible to determine what the correct size should be.
			This option provides an override for these situations.

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	carrier_timeout=
			[NET] Specifies amount of time (in seconds) that
			the kernel should wait for a network carrier. By default
			it waits 120 seconds.

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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.
			format: { id:<keyid> | builtin }

	cca=		[MIPS] Override the kernel pages' cache coherency
			algorithm.  Accepted values range from 0 to 7
			inclusive. See arch/mips/include/asm/pgtable-bits.h
			for platform specific values (SB1, Loongson3 and
			others).

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	ccw_timeout_log	[S390]
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			See Documentation/s390/common_io.rst for details.
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	cgroup_disable=	[KNL] Disable a particular controller
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			Format: {name of the controller(s) to disable}
			The effects of cgroup_disable=foo are:
			- foo isn't auto-mounted if you mount all cgroups in
			  a single hierarchy
			- foo isn't visible as an individually mountable
			  subsystem
			{Currently only "memory" controller deal with this and
			cut the overhead, others just disable the usage. So
			only cgroup_disable=memory is actually worthy}

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	cgroup_no_v1=	[KNL] Disable cgroup controllers and named hierarchies in v1
			Format: { { controller | "all" | "named" }
			          [,{ controller | "all" | "named" }...] }
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			Like cgroup_disable, but only applies to cgroup v1;
			the blacklisted controllers remain available in cgroup2.
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			"all" blacklists all controllers and "named" disables
			named mounts. Specifying both "all" and "named" disables
			all v1 hierarchies.
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	cgroup.memory=	[KNL] Pass options to the cgroup memory controller.
			Format: <string>
			nosocket -- Disable socket memory accounting.
			nokmem -- Disable kernel memory accounting.

	checkreqprot	[SELINUX] Set initial checkreqprot flag value.
			Format: { "0" | "1" }
			See security/selinux/Kconfig help text.
			0 -- check protection applied by kernel (includes
				any implied execute protection).
			1 -- check protection requested by application.
			Default value is set via a kernel config option.
			Value can be changed at runtime via
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				/sys/fs/selinux/checkreqprot.
			Setting checkreqprot to 1 is deprecated.
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	cio_ignore=	[S390]
533
			See Documentation/s390/common_io.rst for details.
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	clk_ignore_unused
			[CLK]
			Prevents the clock framework from automatically gating
			clocks that have not been explicitly enabled by a Linux
			device driver but are enabled in hardware at reset or
			by the bootloader/firmware. Note that this does not
			force such clocks to be always-on nor does it reserve
			those clocks in any way. This parameter is useful for
			debug and development, but should not be needed on a
			platform with proper driver support.  For more
544
			information, see Documentation/driver-api/clk.rst.
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	clock=		[BUGS=X86-32, HW] gettimeofday clocksource override.
			[Deprecated]
			Forces specified clocksource (if available) to be used
			when calculating gettimeofday(). If specified
			clocksource is not available, it defaults to PIT.
			Format: { pit | tsc | cyclone | pmtmr }

	clocksource=	Override the default clocksource
			Format: <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
			[X86-32] pit,hpet,tsc;
				scx200_hrt on Geode; cyclone on IBM x440
			[MIPS] MIPS
			[PARISC] cr16
			[S390] tod
			[SH] SuperH
			[SPARC64] tick
			[X86-64] hpet,tsc

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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.

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	clearcpuid=BITNUM[,BITNUM...] [X86]
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			Disable CPUID feature X for the kernel. See
			arch/x86/include/asm/cpufeatures.h for the valid bit
			numbers. Note the Linux specific bits are not necessarily
			stable over kernel options, but the vendor specific
			ones should be.
			Also note that user programs calling CPUID directly
			or using the feature without checking anything
			will still see it. This just prevents it from
			being used by the kernel or shown in /proc/cpuinfo.
			Also note the kernel might malfunction if you disable
			some critical bits.

	cma=nn[MG]@[start[MG][-end[MG]]]
			[ARM,X86,KNL]
			Sets the size of kernel global memory area for
			contiguous memory allocations and optionally the
			placement constraint by the physical address range of
			memory allocations. A value of 0 disables CMA
			altogether. For more information, see
			include/linux/dma-contiguous.h

	cmo_free_hint=	[PPC] Format: { yes | no }
			Specify whether pages are marked as being inactive
			when they are freed.  This is used in CMO environments
			to determine OS memory pressure for page stealing by
			a hypervisor.
			Default: yes

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

	com20020=	[HW,NET] ARCnet - COM20020 chipset
			Format:
			<io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]

	com90io=	[HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
			Format: <io>[,<irq>]

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

	condev=		[HW,S390] console device
	conmode=

	console=	[KNL] Output console device and options.

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

		ttyS<n>[,options]
		ttyUSB0[,options]
			Use the specified serial port.  The options are of
			the form "bbbbpnf", where "bbbb" is the baud rate,
			"p" is parity ("n", "o", or "e"), "n" is number of
			bits, and "f" is flow control ("r" for RTS or
			omit it).  Default is "9600n8".

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			See Documentation/admin-guide/serial-console.rst for more
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			information.  See
641
			Documentation/networking/netconsole.rst for an
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			alternative.

		uart[8250],io,<addr>[,options]
		uart[8250],mmio,<addr>[,options]
		uart[8250],mmio16,<addr>[,options]
		uart[8250],mmio32,<addr>[,options]
		uart[8250],0x<addr>[,options]
			Start an early, polled-mode console on the 8250/16550
			UART at the specified I/O port or MMIO address,
			switching to the matching ttyS device later.
			MMIO inter-register address stride is either 8-bit
			(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,
			the h/w is not re-initialized.

		hvc<n>	Use the hypervisor console device <n>. This is for
			both Xen and PowerPC hypervisors.

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		If the device connected to the port is not a TTY but a braille
		device, prepend "brl," before the device type, for instance
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			console=brl,ttyS0
		For now, only VisioBraille is supported.

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	console_msg_format=
			[KNL] Change console messages format
		default
			By default we print messages on consoles in
			"[time stamp] text\n" format (time stamp may not be
			printed, depending on CONFIG_PRINTK_TIME or
			`printk_time' param).
		syslog
			Switch to syslog format: "<%u>[time stamp] text\n"
			IOW, each message will have a facility and loglevel
			prefix. The format is similar to one used by syslog()
			syscall, or to executing "dmesg -S --raw" or to reading
			from /proc/kmsg.

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	consoleblank=	[KNL] The console blank (screen saver) timeout in
682
			seconds. A value of 0 disables the blank timer.
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			Defaults to 0.
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	coredump_filter=
			[KNL] Change the default value for
			/proc/<pid>/coredump_filter.
688
			See also Documentation/filesystems/proc.rst.
689

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	coresight_cpu_debug.enable
			[ARM,ARM64]
			Format: <bool>
			Enable/disable the CPU sampling based debugging.
			0: default value, disable debugging
			1: enable debugging at boot time

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

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	cpuidle.governor=
			[CPU_IDLE] Name of the cpuidle governor to use.

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	cpufreq.off=1	[CPU_FREQ]
			disable the cpufreq sub-system

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	cpufreq.default_governor=
			[CPU_FREQ] Name of the default cpufreq governor or
			policy to use. This governor must be registered in the
			kernel before the cpufreq driver probes.

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	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

	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver
			Format:
			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]

	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
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			is selected automatically.
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			[KNL, X86-64] Select a region under 4G first, and
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			fall back to reserve region above 4G when '@offset'
			hasn't been specified.
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			See Documentation/admin-guide/kdump/kdump.rst for further details.
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	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
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			Documentation/admin-guide/kdump/kdump.rst for an example.
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	crashkernel=size[KMG],high
740
			[KNL, X86-64] range could be above 4G. Allow kernel
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			to allocate physical memory region from top, so could
			be above 4G if system have more than 4G ram installed.
			Otherwise memory region will be allocated below 4G, if
			available.
			It will be ignored if crashkernel=X is specified.
	crashkernel=size[KMG],low
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			[KNL, X86-64] range under 4G. When crashkernel=X,high
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			is passed, kernel could allocate physical memory region
			above 4G, that cause second kernel crash on system
			that require some amount of low memory, e.g. swiotlb
			requires at least 64M+32K low memory, 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.
			This one let user to specify own low range under 4G
			for second kernel instead.
			0: to disable low allocation.
			It will be ignored when crashkernel=X,high is not used
			or memory reserved is below 4G.

	cryptomgr.notests
762
			[KNL] Disable crypto self-tests
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775

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

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

	dasd=		[HW,NET]
			See header of drivers/s390/block/dasd_devmap.c.

	db9.dev[2|3]=	[HW,JOY] Multisystem joystick support via parallel port
			(one device per port)
			Format: <port#>,<type>
776
			See also Documentation/input/devices/joystick-parport.rst
777

778
	ddebug_query=	[KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
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			time. See
			Documentation/admin-guide/dynamic-debug-howto.rst for
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			details.  Deprecated, see dyndbg.

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

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	debug_boot_weak_hash
			[KNL] Enable printing [hashed] pointers early in the
			boot sequence.  If enabled, we use a weak hash instead
			of siphash to hash pointers.  Use this option if you are
			seeing instances of '(___ptrval___)') and need to see a
			value (hashed pointer) instead. Cryptographically
			insecure, please do not use on production kernels.

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	debug_locks_verbose=
			[KNL] verbose self-tests
			Format=<0|1>
			Print debugging info while doing the locking API
			self-tests.
			We default to 0 (no extra messages), setting it to
			1 will print _a lot_ more information - normally
			only useful to kernel developers.

	debug_objects	[KNL] Enable object debugging

	no_debug_objects
			[KNL] Disable object debugging

	debug_guardpage_minorder=
			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
			parameter allows control of the order of pages that will
			be intentionally kept free (and hence protected) by the
			buddy allocator. Bigger value increase the probability
			of catching random memory corruption, but reduce the
			amount of memory for normal system use. The maximum
			possible value is MAX_ORDER/2.  Setting this parameter
			to 1 or 2 should be enough to identify most random
			memory corruption problems caused by bugs in kernel or
			driver code when a CPU writes to (or reads from) a
			random memory location. Note that there exists a class
			of memory corruptions problems caused by buggy H/W or
			F/W or by drivers badly programing DMA (basically when
			memory is written at bus level and the CPU MMU is
			bypassed) which are not detectable by
			CONFIG_DEBUG_PAGEALLOC, hence this option will not help
			tracking down these problems.

	debug_pagealloc=
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			[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
			enables the feature at boot time. By default, it is
			disabled and the system will work mostly the same as a
			kernel built without CONFIG_DEBUG_PAGEALLOC.
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			Note: to get most of debug_pagealloc error reports, it's
			useful to also enable the page_owner functionality.
833
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			on: enable the feature

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	debugfs=    	[KNL] This parameter enables what is exposed to userspace
			and debugfs internal clients.
			Format: { on, no-mount, off }
			on: 	All functions are enabled.
			no-mount:
				Filesystem is not registered but kernel clients can
			        access APIs and a crashkernel can be used to read
				its content. There is nothing to mount.
			off: 	Filesystem is not registered and clients
			        get a -EPERM as result when trying to register files
				or directories within debugfs.
				This is equivalent of the runtime functionality if
				debugfs was not enabled in the kernel at all.
			Default value is set in build-time with a kernel configuration.

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	debugpat	[X86] Enable PAT debugging

	decnet.addr=	[HW,NET]
			Format: <area>[,<node>]
854
			See also Documentation/networking/decnet.rst.
855
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	default_hugepagesz=
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			[HW] The size of the default HugeTLB page. This is
			the size represented by the legacy /proc/ hugepages
			APIs.  In addition, this is the default hugetlb size
			used for shmget(), mmap() and mounting hugetlbfs
			filesystems.  If not specified, defaults to the
			architecture's default huge page size.  Huge page
			sizes are architecture dependent.  See also
			Documentation/admin-guide/mm/hugetlbpage.rst.
			Format: size[KMG]
866

867
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	deferred_probe_timeout=
			[KNL] Debugging option to set a timeout in seconds for
			deferred probe to give up waiting on dependencies to
			probe. Only specific dependencies (subsystems or
			drivers) that have opted in will be ignored. A timeout of 0
			will timeout at the end of initcalls. This option will also
			dump out devices still on the deferred probe list after
			retrying.

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	dfltcc=		[HW,S390]
			Format: { on | off | def_only | inf_only | always }
			on:       s390 zlib hardware support for compression on
			          level 1 and decompression (default)
			off:      No s390 zlib hardware support
			def_only: s390 zlib hardware support for deflate
			          only (compression on level 1)
			inf_only: s390 zlib hardware support for inflate
			          only (decompression)
			always:   Same as 'on' but ignores the selected compression
			          level always using hardware support (used for debugging)

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	dhash_entries=	[KNL]
			Set number of hash buckets for dentry cache.

891
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	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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	stress_slb	[PPC]
			Limits the number of kernel SLB entries, and flushes
			them frequently to increase the rate of SLB faults
			on kernel addresses.

902
	disable=	[IPV6]
903
			See Documentation/networking/ipv6.rst.
904

905
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	hardened_usercopy=
                        [KNL] Under CONFIG_HARDENED_USERCOPY, whether
                        hardening is enabled for this boot. Hardened
                        usercopy checking is used to protect the kernel
                        from reading or writing beyond known memory
                        allocation boundaries as a proactive defense
                        against bounds-checking flaws in the kernel's
                        copy_to_user()/copy_from_user() interface.
                on      Perform hardened usercopy checks (default).
                off     Disable hardened usercopy checks.

916
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	disable_radix	[PPC]
			Disable RADIX MMU mode on POWER9

919
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	radix_hcall_invalidate=on  [PPC/PSERIES]
			Disable RADIX GTSE feature and use hcall for TLB
			invalidate.

923
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	disable_tlbie	[PPC]
			Disable TLBIE instruction. Currently does not work
			with KVM, with HASH MMU, or with coherent accelerators.

927
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	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.

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941
	perf_v4_pmi=	[X86,INTEL]
			Format: <bool>
			Disable Intel PMU counter freezing feature.
			The feature only exists starting from
			Arch Perfmon v4 (Skylake and newer).

942
	disable_ddw	[PPC/PSERIES]
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			Disable Dynamic DMA Window support. Use this if
			to workaround buggy firmware.

	disable_ipv6=	[IPV6]
947
			See Documentation/networking/ipv6.rst.
948
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	disable_mtrr_cleanup [X86]
			The kernel tries to adjust MTRR layout from continuous
			to discrete, to make X server driver able to add WB
			entry later. This parameter disables that.

	disable_mtrr_trim [X86, Intel and AMD only]
			By default the kernel will trim any uncacheable
			memory out of your available memory pool based on
			MTRR settings.  This parameter disables that behavior,
			possibly causing your machine to run very slowly.

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

	dis_ucode_ldr	[X86] Disable the microcode loader.

	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.

	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.

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	driver_async_probe=  [KNL]
			List of driver names to be probed asynchronously.
			Format: <driver_name1>,<driver_name2>...

987
	drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
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			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.
			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
997
			available in Documentation/admin-guide/edid.rst. An EDID
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1003
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			data set will only be used for a particular connector,
			if its name and a colon are prepended to the EDID
			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.

	dscc4.setup=	[NET]

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1010
1011
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	dt_cpu_ftrs=	[PPC]
			Format: {"off" | "known"}
			Control how the dt_cpu_ftrs device-tree binding is
			used for CPU feature discovery and setup (if it
			exists).
			off: Do not use it, fall back to legacy cpu table.
			known: Do not pass through unknown features to guests
			or userspace, only those that the kernel is aware of.

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1018
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1020
	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.

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1023
	dyndbg[="val"]		[KNL,DYNAMIC_DEBUG]
	module.dyndbg[="val"]
			Enable debug messages at boot time.  See
1024
1025
			Documentation/admin-guide/dynamic-debug-howto.rst
			for details.
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039

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

	module.async_probe [KNL]
			Enable asynchronous probe on this module.

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

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

1040
1041
1042
1043
			When used with no options, the early console is
			determined by stdout-path property in device tree's
			chosen node or the ACPI SPCR table if supported by
			the platform.
1044

1045
1046
1047
1048
1049
1050
		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.
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092

		uart[8250],io,<addr>[,options]
		uart[8250],mmio,<addr>[,options]
		uart[8250],mmio32,<addr>[,options]
		uart[8250],mmio32be,<addr>[,options]
		uart[8250],0x<addr>[,options]
			Start an early, polled-mode console on the 8250/16550
			UART at the specified I/O port or MMIO address.
			MMIO inter-register address stride is either 8-bit
			(mmio) or 32-bit (mmio32 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
			unspecified, the h/w is not initialized.

		pl011,<addr>
		pl011,mmio32,<addr>
			Start an early, polled-mode console on a pl011 serial
			port at the specified address. The pl011 serial port
			must already be setup and configured. Options are not
			yet supported.  If 'mmio32' is specified, then only
			the driver will use only 32-bit accessors to read/write
			the device registers.

		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.

		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.

1093
1094
1095
1096
1097
1098
		owl,<addr>
			Start an early, polled-mode console on a serial port
			of an Actions Semi SoC, such as S500 or S900, at the
			specified address. The serial port must already be
			setup and configured. Options are not yet supported.

1099
1100
1101
1102
1103
1104
		rda,<addr>
			Start an early, polled-mode console on a serial port
			of an RDA Micro SoC, such as RDA8810PL, at the
			specified address. The serial port must already be
			setup and configured. Options are not yet supported.

1105
1106
1107
1108
		sbi
			Use RISC-V SBI (Supervisor Binary Interface) for early
			console.

1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
		smh	Use ARM semihosting calls for early console.

		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.

1123
1124
1125
1126
1127
1128
		lantiq,<addr>
			Start an early, polled-mode console on a lantiq serial
			(lqasc) port at the specified address. The serial port
			must already be setup and configured. Options are not
			yet supported.

1129
1130
1131
1132
1133
1134
1135
		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.

1136
1137
1138
1139
1140
1141
		ec_imx21,<addr>
		ec_imx6q,<addr>
			Start an early, polled-mode, output-only console on the
			Freescale i.MX UART at the specified address. The UART
			must already be setup and configured.

1142
		ar3700_uart,<addr>
1143
1144
1145
1146
1147
			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.

1148
1149
1150
1151
1152
1153
		qcom_geni,<addr>
			Start an early, polled-mode console on a Qualcomm
			Generic Interface (GENI) based serial port at the
			specified address. The serial port must already be
			setup and configured. Options are not yet supported.

1154
1155
1156
1157
1158
1159
1160
		efifb,[options]
			Start an early, unaccelerated console on the EFI
			memory mapped framebuffer (if available). On cache
			coherent non-x86 systems that use system memory for
			the framebuffer, pass the 'ram' option so that it is
			mapped with the correct attributes.

1161
		linflex,<addr>
1162
			Use early console provided by Freescale LINFlexD UART
1163
1164
1165
1166
			serial driver for NXP S32V234 SoCs. A valid base
			address must be provided, and the serial port must
			already be setup and configured.

1167
	earlyprintk=	[X86,SH,ARM,M68k,S390]
1168
			earlyprintk=vga
1169
			earlyprintk=sclp
1170
1171
1172
1173
1174
			earlyprintk=xen
			earlyprintk=serial[,ttySn[,baudrate]]
			earlyprintk=serial[,0x...[,baudrate]]
			earlyprintk=ttySn[,baudrate]
			earlyprintk=dbgp[debugController#]
1175
			earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1176
			earlyprintk=xdbc[xhciController#]
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204

			earlyprintk is useful when the kernel crashes before
			the normal console is initialized. It is not enabled by
			default because it has some cosmetic problems.

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

			Only one of vga, efi, serial, or usb debug port can
			be used at a time.

			Currently only ttyS0 and ttyS1 may be specified by
			name.  Other I/O ports may be explicitly specified
			on some architectures (x86 and arm at least) by
			replacing ttySn with an I/O port address, like this:
				earlyprintk=serial,0x1008,115200
			You can find the port for a given device in
			/proc/tty/driver/serial:
				2: uart:ST16650V2 port:00001008 irq:18 ...

			Interaction with the standard serial driver is not
			very good.

			The VGA and EFI output is eventually overwritten by
			the real console.

			The xen output can only be used by Xen PV guests.

1205
1206
			The sclp output can only be used on s390.

1207
1208
1209
1210
			The optional "force" to "pciserial" enables use of a
			PCI device even when its classcode is not of the
			UART class.

1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
	edac_report=	[HW,EDAC] Control how to report EDAC event
			Format: {"on" | "off" | "force"}
			on: enable EDAC to report H/W event. May be overridden
			by other higher priority error reporting module.
			off: disable H/W event reporting through EDAC.
			force: enforce the use of EDAC to report H/W event.
			default: on.

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

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

1225
1226
1227
1228
1229
			This parameter works in place of the kgdboc parameter
			but can only be used if the backing tty is available
			very early in the boot process. For early debugging
			via a serial port see kgdboc_earlycon instead.

1230
1231
1232
1233
	edd=		[EDD]
			Format: {"off" | "on" | "skip[mbr]"}

	efi=		[EFI]
1234
1235
1236
1237
1238
1239
			Format: { "debug", "disable_early_pci_dma",
				  "nochunk", "noruntime", "nosoftreserve",
				  "novamap", "no_disable_early_pci_dma" }
			debug: enable misc debug output.
			disable_early_pci_dma: disable the busmaster bit on all
			PCI bridges while in the EFI boot stub.
1240
1241
1242
1243
			nochunk: disable reading files in "chunks" in the EFI
			boot stub, as chunking can cause problems with some
			firmware implementations.
			noruntime : disable EFI runtime services support
1244
1245
1246
1247
1248
1249
			nosoftreserve: The EFI_MEMORY_SP (Specific Purpose)
			attribute may cause the kernel to reserve the
			memory range for a memory mapping driver to
			claim. Specify efi=nosoftreserve to disable this
			reservation and treat the memory by its base type
			(i.e. EFI_CONVENTIONAL_MEMORY / "System RAM").
1250
			novamap: do not call SetVirtualAddressMap().
1251
1252
			no_disable_early_pci_dma: Leave the busmaster bit set
			on all PCI bridges while in the EFI boot stub
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264

	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.

	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.
1265

1266
1267
1268
1269
1270
			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.

1271
1272
1273
1274
			If efi_fake_mem=8G@9G:0x40000 is specified, the
			EFI_MEMORY_SP(0x40000) attribute is added to
			range 0x240000000-0x43fffffff.

1275
			Using this parameter you can do debugging of EFI memmap
1276
			related features. For example, you can do debugging of
1277
			Address Range Mirroring feature even if your box
1278
1279
			doesn't support it, or mark specific memory as
			"soft reserved".
1280

1281
1282
1283
1284
	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
1285
			Documentation/admin-guide/acpi/ssdt-overlays.rst for details.
1286
1287


1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
	eisa_irq_edge=	[PARISC,HW]
			See header of drivers/parisc/eisa.c.

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

	elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
			Specifies physical address of start of kernel core
			image elf header and optionally the size. Generally
			kexec loader will pass this option to capture kernel.
1299
			See Documentation/admin-guide/kdump/kdump.rst for details.
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317

	enable_mtrr_cleanup [X86]
			The kernel tries to adjust MTRR layout from continuous
			to discrete, to make X server driver able to add WB
			entry later. This parameter enables that.

	enable_timer_pin_1 [X86]
			Enable PIN 1 of APIC timer
			Can be useful to work around chipset bugs
			(in particular on some ATI chipsets).
			The kernel tries to set a reasonable default.

	enforcing	[SELINUX] Set initial enforcing status.
			Format: {"0" | "1"}
			See security/selinux/Kconfig help text.
			0 -- permissive (log only, no denials).
			1 -- enforcing (deny and log).
			Default value is 0.
1318
1319
			Value can be changed at runtime via
			/sys/fs/selinux/enforce.
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341

	erst_disable	[ACPI]
			Disable Error Record Serialization Table (ERST)
			support.

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

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

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

	floppy=		[HW]
1342
			See Documentation/admin-guide/blockdev/floppy.rst.
1343
1344
1345
1346
1347
1348
1349

	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.

1350
	forcepae	[X86-32]
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
			Forcefully enable Physical Address Extension (PAE).
			Many Pentium M systems disable PAE but may have a
			functionally usable PAE implementation.
			Warning: use of this parameter will taint the kernel
			and may cause unknown problems.

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

	ftrace_dump_on_oops[=orig_cpu]
			[FTRACE] will dump the trace buffers on oops.
			If no parameter is passed, ftrace will dump
			buffers of all CPUs, but if you pass orig_cpu, it will
			dump only the buffer of the CPU that triggered the
			oops.

	ftrace_filter=[function-list]
			[FTRACE] Limit the functions traced by the function
			tracer at boot up. function-list is a comma separated
			list of functions. This list can be changed at run
			time by the set_ftrace_filter file in the debugfs
			tracing directory.

	ftrace_notrace=[function-list]
			[FTRACE] Do not trace the functions specified in
			function-list. This list can be changed at run time
			by the set_ftrace_notrace file in the debugfs
			tracing directory.

	ftrace_graph_filter=[function-list]
			[FTRACE] Limit the top level callers functions traced
			by the function graph tracer at boot up.
			function-list is a comma separated list of functions
			that can be changed at run time by the
			set_graph_function file in the debugfs tracing directory.

	ftrace_graph_notrace=[function-list]
			[FTRACE] Do not trace from the functions specified in
			function-list.  This list is a comma separated list of
			functions that can be changed at run time by the
			set_graph_notrace file in the debugfs tracing directory.

1395
1396
1397
1398
1399
1400
	ftrace_graph_max_depth=<uint>
			[FTRACE] Used with the function graph tracer. This is
			the max depth it will trace into a function. This value
			can be changed at run time by the max_graph_depth file
			in the tracefs tracing directory. default: 0 (no limit)

1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
	fw_devlink=	[KNL] Create device links between consumer and supplier
			devices by scanning the firmware to infer the
			consumer/supplier relationships. This feature is
			especially useful when drivers are loaded as modules as
			it ensures proper ordering of tasks like device probing
			(suppliers first, then consumers), supplier boot state
			clean up (only after all consumers have probed),
			suspend/resume & runtime PM (consumers first, then
			suppliers).
			Format: { off | permissive | on | rpm }
			off --	Don't create device links from firmware info.
			permissive -- Create device links from firmware info
				but use it only for ordering boot state clean
				up (sync_state() calls).
			on -- 	Create device links from firmware info and use it
				to enforce probe and suspend/resume ordering.
			rpm --	Like "on", but also use to order runtime PM.

1419
1420
1421
1422
	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>
1423
			See also Documentation/input/devices/joystick-parport.rst
1424
1425
1426

	gamma=		[HW,DRM]

1427
	gart_fix_e820=	[X86-64] disable the fix e820 for K8 GART
1428
1429
1430
1431
1432
1433
1434
1435
1436
			Format: off | on
			default: on

	gcov_persist=	[GCOV] When non-zero (default), profiling data for
			kernel modules is saved and remains accessible via
			debugfs, even when the module is unloaded/reloaded.
			When zero, profiling data is discarded and associated
			debugfs files are removed at module unload time.

1437
1438
1439
1440
	goldfish	[X86] Enable the goldfish android emulator platform.
			Don't use this when you are not running on the
			android emulator

1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
	gpt		[EFI] Forces disk with valid GPT signature but
			invalid Protective MBR to be treated as GPT. If the
			primary GPT is corrupted, it enables the backup/alternate
			GPT to be used instead.

	grcan.enable0=	[HW] Configuration of physical interface 0. Determines
			the "Enable 0" bit of the configuration register.
			Format: 0 | 1
			Default: 0
	grcan.enable1=	[HW] Configuration of physical interface 1. Determines
			the "Enable 0" bit of the configuration register.
			Format: 0 | 1
			Default: 0
	grcan.select=	[HW] Select which physical interface to use.
			Format: 0 | 1
			Default: 0
	grcan.txsize=	[HW] Sets the size of the tx buffer.
			Format: <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

1464
1465
1466
1467
	gpio-mockup.gpio_mockup_ranges
			[HW] Sets the ranges of gpiochip of for this device.
			Format: <start1>,<end1>,<start2>,<end2>...

1468
1469
1470
	hardlockup_all_cpu_backtrace=
			[KNL] Should the hard-lockup detector generate
			backtraces on all cpus.
1471
			Format: 0 | 1
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509

	hashdist=	[KNL,NUMA] Large hashes allocated during boot
			are distributed across NUMA nodes.  Defaults on
			for 64-bit NUMA, off otherwise.
			Format: 0 | 1 (for off | on)

	hcl=		[IA-64] SGI's Hardware Graph compatibility layer

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

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

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

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

	hlt		[BUGS=ARM,SH]

	hpet=		[X86-32,HPET] option to control HPET usage
			Format: { enable (default) | disable | force |
				verbose }
			disable: disable HPET and use PIT instead
			force: allow force enabled of undocumented chips (ICH4,
				VIA, nVidia)
			verbose: show contents of HPET registers during setup

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

1510
1511
1512
1513
1514
1515
1516
1517
	hugetlb_cma=	[HW] The size of a cma area used for allocation
			of gigantic hugepages.
			Format: nn[KMGTPE]

			Reserve a cma area of given size and allocate gigantic
			hugepages using the cma allocator. If enabled, the
			boot-time allocation of gigantic hugepages is skipped.

1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
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	hugepages=	[HW] Number of HugeTLB pages to allocate at boot.
			If this follows hugepagesz (below), it specifies
			the number of pages of hugepagesz to be allocated.
			If this is the first HugeTLB parameter on the command
			line, it specifies the number of pages to allocate for
			the default huge page size.  See also
			Documentation/admin-guide/mm/hugetlbpage.rst.
			Format: <integer>

	hugepagesz=
			[HW] The size of the HugeTLB pages.  This is used in
			conjunction with hugepages (above) to allocate huge
			pages of a specific size at boot.  The pair
			hugepagesz=X hugepages=Y can be specified once for
			each supported huge page size. Huge page sizes are
			architecture dependent.  See also
			Documentation/admin-guide/mm/hugetlbpage.rst.
			Format: size[KMG]
1536

1537
1538
	hung_task_panic=
			[KNL] Should the hung task detector generate panics.
1539
			Format: 0 | 1
1540

1541
			A value of 1 instructs the kernel to panic when a
1542
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			hung task is detected. The default value is controlled
			by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
			option. The value selected by this boot parameter can
			be changed later by the kernel.hung_task_panic sysctl.

	hvc_iucv=	[S390]	Number of z/VM IUCV hypervisor console (HVC)
				terminal devices. Valid values: 0..8
	hvc_iucv_allow=	[S390]	Comma-separated list of z/VM user IDs.
				If specified, z/VM IUCV HVC accepts connections
				from listed z/VM user IDs only.
1552
1553
1554
1555
1556

	hv_nopvspin	[X86,HYPER_V] Disables the paravirt spinlock optimizations
				      which allow the hypervisor to 'idle' the
				      guest on lock contention.

1557
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1559
1560
1561
1562
	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.

1563
1564
1565
1566
1567
	i2c_bus=	[HW]	Override the default board specific I2C bus speed
				or register an additional I2C bus that is not
				registered from board initialization code.
				Format:
				<bus_id>,<clkrate>
1568
1569
1570
1571
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1574
1575
1576
1577
1578
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1581
1582
1583
1584
1585
1586

	i8042.debug	[HW] Toggle i8042 debug mode
	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)
	i8042.direct	[HW] Put keyboard port into non-translated mode
	i8042.dumbkbd	[HW] Pretend that controller can only read data from
			     keyboard and cannot control its state
			     (Don't attempt to blink the leds)
	i8042.noaux	[HW] Don't check for auxiliary (== mouse) port
	i8042.nokbd	[HW] Don't check/create keyboard port
	i8042.noloop	[HW] Disable the AUX Loopback command while probing
			     for the AUX port
	i8042.nomux	[HW] Don't check presence of an active multiplexing
			     controller
	i8042.nopnp	[HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
			     controllers
	i8042.notimeout	[HW] Ignore timeout condition signalled by controller
1587
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1589
1590
1591
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1594
	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
1595
	i8042.unlock	[HW] Unlock (ignore) the keylock
1596
	i8042.kbdreset	[HW] Reset device connected to KBD port
1597
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1630
1631

	i810=		[HW,DRM]

	i8k.ignore_dmi	[HW] Continue probing hardware even if DMI data
			indicates that the driver is running on unsupported
			hardware.
	i8k.force	[HW] Activate i8k driver even if SMM BIOS signature
			does not match list of supported models.
	i8k.power_status
			[HW] Report power status in /proc/i8k
			(disabled by default)
	i8k.restricted	[HW] Allow controlling fans only if SYS_ADMIN
			capability is set.

	i915.invert_brightness=
			[DRM] Invert the sense of the variable that is used to
			set the brightness of the panel backlight. Normally a
			brightness value of 0 indicates backlight switched off,
			and the maximum of the brightness value sets the backlight
			to maximum brightness. If this parameter is set to 0
			(default) and the machine requires it, or this parameter
			is set to 1, a brightness value of 0 sets the backlight
			to maximum brightness, and the maximum of the brightness
			value switches the backlight off.
			-1 -- never invert brightness
			 0 -- machine default
			 1 -- force brightness inversion

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

	ide-core.nodma=	[HW] (E)IDE subsystem
			Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
			.vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
			.cdrom .chs .ignore_cable are additional options
1632
			See Documentation/ide/ide.rst.
1633
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1700
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1702
1703
1704
1705
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1707
1708
1709
1710
1711
1712

	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.

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

	idle=		[X86]
			Format: idle=poll, idle=halt, idle=nomwait
			Poll forces a polling idle loop that can slightly
			improve the performance of waking up a idle CPU, but
			will use a lot of power and make the system run hot.
			Not recommended.
			idle=halt: Halt is forced to be used for CPU idle.
			In such case C2/C3 won't be used again.
			idle=nomwait: Disable mwait for CPU C-states

	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.

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

	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.

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

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

1713
	ima_appraise_tcb [IMA] Deprecated.  Use ima_policy= instead.
1714
1715
1716
			The builtin appraise policy appraises all files
			owned by uid=0.

1717
1718
1719
1720
	ima_canonical_fmt [IMA]
			Use the canonical format for the binary runtime
			measurements, instead of host native format.

1721
1722
1723
1724
1725
1726
1727
1728
1729
	ima_hash=	[IMA]
			Format: { md5 | sha1 | rmd160 | sha256 | sha384
				   | sha512 | ... }
			default: "sha1"

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

	ima_policy=	[IMA]
1730
			The builtin policies to load during IMA setup.
1731
1732
			Format: "tcb | appraise_tcb | secure_boot |
				 fail_securely"
1733
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1739

			The "tcb" policy 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.

			The "appraise_tcb" policy appraises the integrity of
1740
			all files owned by root.
1741
1742
1743
1744

			The "secure_boot" policy appraises the integrity
			of files (eg. kexec kernel image, kernel modules,
			firmware, policy, etc) based on file signatures.
1745

1746
1747
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1749
1750
			The "fail_securely" policy forces file signature
			verification failure also on privileged mounted
			filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
			flag.

1751
1752
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1754
1755
1756
	ima_tcb		[IMA] Deprecated.  Use ima_policy= instead.
			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.

1757
	ima_template=	[IMA]
1758
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1761
1762
			Select one of defined IMA measurements template formats.
			Formats: { "ima" | "ima-ng" | "ima-sig" }
			Default: "ima-ng"

	ima_template_fmt=
1763
			[IMA] Define a custom template format.
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			Format: { "field1|...|fieldN" }

	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.

	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.

	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.

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

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

1798
1799
1800
1801
1802
1803
1804
	initrdmem=	[KNL] Specify a physical address and size from which to
			load the initrd. If an initrd is compiled in or
			specified in the bootparams, it takes priority over this
			setting.
			Format: ss[KMG],nn[KMG]
			Default is 0, 0

1805
1806
1807
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1810
1811
1812
1813
	init_on_alloc=	[MM] Fill newly allocated pages and heap objects with
			zeroes.
			Format: 0 | 1
			Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.

	init_on_free=	[MM] Fill freed pages and heap objects with zeroes.
			Format: 0 | 1
			Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.

1814
	init_pkru=	[X86] Specify the default memory protection keys rights
1815
1816
1817
1818
			register contents for all processes.  0x55555554 by
			default (disallow access to all but pkey 0).  Can
			override in debugfs after boot.

1819
1820
1821
	inport.irq=	[HW] Inport (ATI XL and Microsoft) busmouse driver
			Format: <irq>

1822
	int_pln_enable	[X86] Enable power limit notification interrupt
1823
1824
1825
1826
1827
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1829
1830
1831
1832
1833
1834
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1836
1837
1838
1839

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

	intel_iommu=	[DMAR] Intel IOMMU driver (DMAR) option
		on
			Enable intel iommu driver.
		off
			Disable intel iommu driver.
		igfx_off [Default Off]
			By default, gfx is mapped as normal device. If a gfx
			device has a dedicated DMAR unit, the DMAR unit is
			bypassed by not enabling DMAR with this option. In
			this case, gfx device will use physical address for
			DMA.
1840
		forcedac [X86-64]
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
			With this option iommu will not optimize to look
			for io virtual address below 32-bit forcing dual
			address cycle on pci bus for cards supporting greater
			than 32-bit addressing. The default is to look
			for translation below 32-bit and if not available
			then look in the higher range.
		strict [Default Off]
			With this option on every unmap_single operation will
			result in a hardware IOTLB flush operation as opposed
			to batching them for performance.
		sp_off [Default Off]
			By default, super page will be supported if Intel IOMMU
			has the capability. With this option, super page will
			not be supported.
1855
1856
1857
1858
1859
		sm_on [Default Off]
			By default, scalable mode will be disabled even if the
			hardware advertises that it has support for the scalable
			mode translation. With this option set, scalable mode
			will be used on hardware which claims to support it.
1860
1861
1862
1863
1864
1865
1866
1867
1868
		tboot_noforce [Default Off]
			Do not force the Intel IOMMU enabled under tboot.
			By default, tboot will force Intel IOMMU on, which
			could harm performance of some high-throughput
			devices like 40GBit network cards, even if identity
			mapping is enabled.
			Note that using this option lowers the security
			provided by tboot because it makes the system
			vulnerable to DMA attacks.
1869
		nobounce [Default off]
1870
			Disable bounce buffer for untrusted devices such as
1871
1872
1873
			the Thunderbolt devices. This will treat the untrusted
			devices as the trusted ones, hence might expose security
			risks of DMA attacks.
1874
1875
1876

	intel_idle.max_cstate=	[KNL,HW,ACPI,X86]
			0	disables intel_idle and fall back on acpi_idle.
1877
			1 to 9	specify maximum depth of C-state.
1878

1879
1880
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1900
1901
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1908
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1910
1911
	intel_pstate=	[X86]
			disable
			  Do not enable intel_pstate as the default
			  scaling driver for the supported processors
			passive
			  Use intel_pstate as a scaling driver, but configure it
			  to work with generic cpufreq governors (instead of
			  enabling its internal governor).  This mode cannot be
			  used along with the hardware-managed P-states (HWP)
			  feature.
			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.
			no_hwp
			  Do not enable hardware P state control (HWP)
			  if available.
			hwp_only
			  Only load intel_pstate on systems which support
			  hardware P state control (HWP) if available.
			support_acpi_ppc
			  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.
			per_cpu_perf_limits
			  Allow per-logical-CPU P-State performance control limits using
			  cpufreq sysfs interface
1912
1913
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1917
1918
1919
1920
1921
1922
1923
1924

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

	iomem=		Disable strict checking of access to MMIO memory
		strict	regions from userspace.
		relaxed

1925
	iommu=		[X86]
1926
1927
1928
1929
1930
1931
1932
1933
1934
		off
		force
		noforce
		biomerge
		panic
		nopanic
		merge
		nomerge
		soft
1935
1936
		pt		[X86]
		nopt		[X86]
1937
1938
1939
		nobypass	[PPC/POWERNV]
			Disable IOMMU bypass, using IOMMU for PCI devices.

1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
			Format: { "0" | "1" }
			0 - Lazy mode.
			  Request that DMA unmap operations use deferred
			  invalidation of hardware TLBs, for increased
			  throughput at the cost of reduced device isolation.
			  Will fall back to strict mode if not supported by
			  the relevant IOMMU driver.
			1 - Strict mode (default).
			  DMA unmap operations invalidate IOMMU hardware TLBs
			  synchronously.

1952
	iommu.passthrough=
1953
			[ARM64, X86] Configure DMA to bypass the IOMMU by default.
1954
1955
1956
			Format: { "0" | "1" }
			0 - Use IOMMU translation for DMA.
			1 - Bypass the IOMMU for DMA.
1957
			unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973

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

	io_delay=	[X86] I/O delay method
		0x80
			Standard port 0x80 based delay
		0xed
			Alternate port 0xed based delay (needed on some systems)
		udelay
			Simple two microseconds delay
		none
			No delay

	ip=		[IP_PNP]
1974
			See Documentation/admin-guide/nfs/nfsroot.rst.
1975

1976
1977
1978
	ipcmni_extend	[KNL] Extend the maximum number of unique System V
			IPC identifiers from 32,768 to 16,777,216.

1979
	irqaffinity=	[SMP] Set the default irq affinity mask
1980
			The argument is a cpu list, as described above.
1981

1982
1983
1984
1985
1986
1987
1988
	irqchip.gicv2_force_probe=
			[ARM, ARM64]
			Format: <bool>
			Force the kernel to look for the second 4kB page
			of a GICv2 controller even if the memory range
			exposed by the device tree is too small.

1989
1990
1991
1992
1993
1994
1995
1996
	irqchip.gicv3_nolpi=
			[ARM, ARM64]
			Force the kernel to ignore the availability of
			LPIs (and by consequence ITSs). Intended for system
			that use the kernel as a bootloader, and thus want
			to let secondary kernels in charge of setting up
			LPIs.

1997
1998
1999
2000
2001
	irqchip.gicv3_pseudo_nmi= [ARM64]
			Enables support for pseudo-NMIs in the kernel. This
			requires the kernel to be built with
			CONFIG_ARM64_PSEUDO_NMI.

2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
	irqfixup	[HW]
			When an interrupt is not handled search all handlers
			for it. Intended to get systems with badly broken
			firmware running.

	irqpoll		[HW]
			When an interrupt is not handled search all handlers
			for it. Also check all handlers each timer
			interrupt. Intended to get systems with badly broken
			firmware running.

	isapnp=		[ISAPNP]
			Format: <RDP>,<reset>,<pci_scan>,<verbosity>

2016
2017
2018
2019
2020
2021
2022
2023
2024
	isolcpus=	[KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
			[Deprecated - use cpusets instead]
			Format: [flag-list,]<cpu-list>

			Specify one or more CPUs to isolate from disturbances
			specified in the flag list (default: domain):

			nohz
			  Disable the tick when a single task runs.
2025
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			  A residual 1Hz tick is offloaded to workqueues, which you
			  need to affine to housekeeping through the global
			  workqueue's affinity configured via the
			  /sys/devices/virtual/workqueue/cpumask sysfs file, or
			  by using the 'domain' flag described below.

			  NOTE: by default the global workqueue runs on all CPUs,
			  so to protect individual CPUs the 'cpumask' file has to
			  be configured manually after bootup.

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			domain
			  Isolate from the general SMP balancing and scheduling
			  algorithms. Note that performing domain isolation this way
			  is irreversible: it's not possible to bring back a CPU to
			  the domains once isolated through isolcpus. It's strongly
			  advised to use cpusets instead to disable scheduler load
			  balancing through the "cpuset.sched_load_balance" file.
			  It offers a much more flexible interface where CPUs can
			  move in and out of an isolated set anytime.

			  You can move a process onto or off an "isolated" CPU via
			  the CPU affinity syscalls or cpuset.
			  <cpu number> begins at 0 and the maximum value is
			  "number of CPUs in system - 1".

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			managed_irq

			  Isolate from being targeted by managed interrupts
			  which have an interrupt mask containing isolated
			  CPUs. The affinity of managed interrupts is
			  handled by the kernel and cannot be changed via
			  the /proc/irq/* interfaces.

			  This isolation is best effort and only effective
			  if the automatically assigned interrupt mask of a
			  device queue contains isolated and housekeeping
			  CPUs. If housekeeping CPUs are online then such
			  interrupts are directed to the housekeeping CPU
			  so that IO submitted on the housekeeping CPU
			  cannot disturb the isolated CPU.

			  If a queue's affinity mask contains only isolated
			  CPUs then this parameter has no effect on the
			  interrupt routing decision, though interrupts are
			  only delivered when tasks running on those
			  isolated CPUs submit IO. IO submitted on
			  housekeeping CPUs has no influence on those
			  queues.
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			The format of <cpu-list> is described above.
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	iucv=		[HW,NET]

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	ivrs_ioapic	[HW,X86-64]
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			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

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	ivrs_hpet	[HW,X86-64]
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			Provide an override to the HPET-ID<->DEVICE-ID
			mapping provided in the IVRS ACPI table. For
			example, to map HPET-ID decimal 0 to
			PCI device 00:14.0 write the parameter as:
				ivrs_hpet[0]=00:14.0

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	ivrs_acpihid	[HW,X86-64]
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			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

	js=		[HW,JOY] Analog joystick
2101
			See Documentation/input/joydev/joystick.rst.
2102

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	nokaslr		[KNL]
			When CONFIG_RANDOMIZE_BASE is set, this disables
			kernel and module base offset ASLR (Address Space
			Layout Randomization).
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	kasan_multi_shot
			[KNL] Enforce KASAN (Kernel Address Sanitizer) to print
			report on every invalid memory access. Without this
			parameter KASAN will print report only for the first
			invalid access.

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	keepinitrd	[HW,ARM]

	kernelcore=	[KNL,X86,IA-64,PPC]
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			Format: nn[KMGTPE] | nn% | "mirror"
			This parameter specifies the amount of memory usable by
			the kernel for non-movable allocations.  The requested
			amount is spread evenly throughout all nodes in the
			system as ZONE_NORMAL.  The remaining memory is used for
			movable memory in its own zone, ZONE_MOVABLE.  In the
			event, a node is too small to have both ZONE_NORMAL and
			ZONE_MOVABLE, kernelcore memory will take priority and
			other nodes will have a larger ZONE_MOVABLE.

			ZONE_MOVABLE is used for the allocation of pages that
			may be reclaimed or moved by the page migration
			subsystem.  Note that allocations like PTEs-from-HighMem
			still use the HighMem zone if it exists, and the Normal
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			zone if it does not.

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			It is possible to specify the exact amount of memory in
			the form of "nn[KMGTPE]", a percentage of total system
			memory in the form of "nn%", or "mirror".  If "mirror"
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			option is specified, mirrored (reliable) memory is used
			for non-movable allocations and remaining memory is used
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			for Movable pages.  "nn[KMGTPE]", "nn%", and "mirror"
			are exclusive, so you cannot specify multiple forms.
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	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.

	kgdboc=		[KGDB,HW] kgdb over consoles.
			Requires a tty driver that supports console polling,
			or a supported polling keyboard driver (non-usb).
			 Serial only format: <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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	kgdboc_earlycon=	[KGDB,HW]
			If the boot console provides the ability to read
			characters and can work in polling mode, you can use
			this parameter to tell kgdb to use it as a backend
			until the normal console is registered. Intended to
			be used together with the kgdboc parameter which
			specifies the normal console to transition to.

			The name of the early console should be specified
			as the value of this parameter. Note that the name of
			the early console might be different than the tty
			name passed to kgdboc. It's OK to leave the value
			blank and the first boot console that implements
			read() will be picked.

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	kgdbwait	[KGDB] Stop kernel execution and enter the
			kernel debugger at the earliest opportunity.

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

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

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	kprobe_event=[probe-list]
			[FTRACE] Add kprobe events and enable at boot time.
			The probe-list is a semicolon delimited list of probe
			definitions. Each definition is same as kprobe_events
			interface, but the parameters are comma delimited.
			For example, to add a kprobe event on vfs_read with
			arg1 and arg2, add to the command line;

			      kprobe_event=p,vfs_read,$arg1,$arg2

			See also Documentation/trace/kprobetrace.rst "Kernel