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linux/Documentation/admin-guide/kernel-parameters.txt
Linus Torvalds 077d3dafe6 Merge branch 'core-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 
Pull watchdog core update from Thomas Gleixner:
 "A single commit adding a command line parameter which allows to set
  the watchdog threshold on the kernel command-line, so kernels with
  massive debug facilities enabled won't trigger the watchdog during
  early boot and before the threshold can be changed via sysctl"

* 'core-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  watchdog/core: Add watchdog_thresh command line parameter
2019-03-10 13:46:08 -07:00

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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
See also Documentation/power/runtime_pm.txt, pci=noacpi
acpi_apic_instance= [ACPI, IOAPIC]
Format: <int>
2: use 2nd APIC table, if available
1,0: use 1st APIC table
default: 0
acpi_backlight= [HW,ACPI]
acpi_backlight=vendor
acpi_backlight=video
If set to vendor, prefer vendor specific driver
(e.g. thinkpad_acpi, sony_acpi, etc.) instead
of the ACPI video.ko driver.
acpi_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
Documentation/acpi/debug.txt for more information about
debug layers and levels.
Enable processor driver info messages:
acpi.debug_layer=0x20000000
Enable PCI/PCI interrupt routing info messages:
acpi.debug_layer=0x400000
Enable AML "Debug" output, i.e., stores to the Debug
object while interpreting AML:
acpi.debug_layer=0xffffffff acpi.debug_level=0x2
Enable all messages related to ACPI hardware:
acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
Some values produce so much output that the system is
unusable. The "log_buf_len" parameter may be useful
if you need to capture more output.
acpi_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>...
acpi_mask_gpe= [HW,ACPI]
Due to the existence of _Lxx/_Exx, some GPEs triggered
by unsupported hardware/firmware features can result in
GPE floodings that cannot be automatically disabled by
the GPE dispatcher.
This facility can be used to prevent such uncontrolled
GPE floodings.
Format: <int>
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.
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,
old_ordering, nonvs, sci_force_enable, nobl }
See Documentation/power/video.txt for information on
s3_bios and s3_mode.
s3_beep is for debugging; it makes the PC's speaker beep
as soon as the kernel's real-mode entry point is called.
s4_nohwsig prevents ACPI hardware signature from being
used during resume from hibernation.
old_ordering causes the ACPI 1.0 ordering of the _PTS
control method, with respect to putting devices into
low power states, to be enforced (the ACPI 2.0 ordering
of _PTS is used by default).
nonvs prevents the kernel from saving/restoring the
ACPI NVS memory during suspend/hibernation and resume.
sci_force_enable causes the kernel to set SCI_EN directly
on resume from S1/S3 (which is against the ACPI spec,
but some broken systems don't work without it).
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).
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]
See Documentation/sound/alsa-configuration.rst
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.
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.)
amijoy.map= [HW,JOY] Amiga joystick support
Map of devices attached to JOY0DAT and JOY1DAT
Format: <a>,<b>
See also Documentation/input/joydev/joystick.rst
analog.map= [HW,JOY] Analog joystick and gamepad support
Specifies type or capabilities of an analog joystick
connected to one of 16 gameports
Format: <type1>,<type2>,..<type16>
apc= [HW,SPARC]
Power management functions (SPARCstation-4/5 + deriv.)
Format: noidle
Disable APC CPU standby support. SPARCstation-Fox does
not play well with APC CPU idle - disable it if you have
APC and your system crashes randomly.
apic= [APIC,X86] Advanced Programmable Interrupt Controller
Change the output verbosity while booting
Format: { quiet (default) | verbose | debug }
Change the amount of debugging information output
when initialising the APIC and IO-APIC components.
For X86-32, this can also be used to specify an APIC
driver name.
Format: apic=driver_name
Examples: apic=bigsmp
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]
See Documentation/networking/ipv6.txt.
show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
Limit apic dumping. The parameter defines the maximal
number of local apics being dumped. Also it is possible
to set it to "all" by meaning -- no limit here.
Format: { 1 (default) | 2 | ... | all }.
The parameter valid if only apic=debug or
apic=verbose is specified.
Example: apic=debug show_lapic=all
apm= [APM] Advanced Power Management
See header of arch/x86/kernel/apm_32.c.
arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
Format: <io>,<irq>,<nodeID>
ataflop= [HW,M68k]
atarimouse= [HW,MOUSE] Atari Mouse
atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
EzKey and similar keyboards
atkbd.reset= [HW] Reset keyboard during initialization
atkbd.set= [HW] Select keyboard code set
Format: <int> (2 = AT (default), 3 = PS/2)
atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
keyboards
atkbd.softraw= [HW] Choose between synthetic and real raw mode
Format: <bool> (0 = real, 1 = synthetic (default))
atkbd.softrepeat= [HW]
Use software keyboard repeat
audit= [KNL] Enable the audit sub-system
Format: { "0" | "1" | "off" | "on" }
0 | off - kernel audit is disabled and can not be
enabled until the next reboot
unset - kernel audit is initialized but disabled and
will be fully enabled by the userspace auditd.
1 | 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.
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.
See Documentation/block/cmdline-partition.txt
boot_delay= Milliseconds to delay each printk during boot.
Values larger than 10 seconds (10000) are changed to
no delay (0).
Format: integer
bootmem_debug [KNL] Enable bootmem allocator debug messages.
bert_disable [ACPI]
Disable BERT OS support on buggy BIOSes.
bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
bttv.radio= Most important insmod options are available as
kernel args too.
bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
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.
carrier_timeout=
[NET] Specifies amount of time (in seconds) that
the kernel should wait for a network carrier. By default
it waits 120 seconds.
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).
ccw_timeout_log [S390]
See Documentation/s390/CommonIO for details.
cgroup_disable= [KNL] Disable a particular controller
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}
cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1
Format: { { controller | "all" | "named" }
[,{ controller | "all" | "named" }...] }
Like cgroup_disable, but only applies to cgroup v1;
the blacklisted controllers remain available in cgroup2.
"all" blacklists all controllers and "named" disables
named mounts. Specifying both "all" and "named" disables
all v1 hierarchies.
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
/selinux/checkreqprot.
cio_ignore= [S390]
See Documentation/s390/CommonIO for details.
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
information, see Documentation/driver-api/clk.rst.
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
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.
clearcpuid=BITNUM [X86]
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".
See Documentation/admin-guide/serial-console.rst for more
information. See
Documentation/networking/netconsole.txt for an
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.
If the device connected to the port is not a TTY but a braille
device, prepend "brl," before the device type, for instance
console=brl,ttyS0
For now, only VisioBraille is supported.
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.
consoleblank= [KNL] The console blank (screen saver) timeout in
seconds. A value of 0 disables the blank timer.
Defaults to 0.
coredump_filter=
[KNL] Change the default value for
/proc/<pid>/coredump_filter.
See also Documentation/filesystems/proc.txt.
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
cpuidle.off=1 [CPU_IDLE]
disable the cpuidle sub-system
cpuidle.governor=
[CPU_IDLE] Name of the cpuidle governor to use.
cpufreq.off=1 [CPU_FREQ]
disable the cpufreq sub-system
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
is selected automatically. Check
Documentation/kdump/kdump.txt for further details.
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
Documentation/kdump/kdump.txt for an example.
crashkernel=size[KMG],high
[KNL, x86_64] range could be above 4G. Allow kernel
to allocate physical memory region from top, so could
be above 4G if system have more than 4G ram installed.
Otherwise memory region will be allocated below 4G, if
available.
It will be ignored if crashkernel=X is specified.
crashkernel=size[KMG],low
[KNL, x86_64] range under 4G. When crashkernel=X,high
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
[KNL] Disable crypto self-tests
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>
See also Documentation/input/devices/joystick-parport.rst
ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
time. See
Documentation/admin-guide/dynamic-debug-howto.rst for
details. Deprecated, see dyndbg.
debug [KNL] Enable kernel debugging (events log level).
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.
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=
[KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
parameter enables the feature at boot time. In
default, it is disabled. We can avoid allocating huge
chunk of memory for debug pagealloc if we don't enable
it at boot time and the system will work mostly same
with the kernel built without CONFIG_DEBUG_PAGEALLOC.
on: enable the feature
debugpat [X86] Enable PAT debugging
decnet.addr= [HW,NET]
Format: <area>[,<node>]
See also Documentation/networking/decnet.txt.
default_hugepagesz=
[same as hugepagesz=] The size of the default
HugeTLB page size. This is the size represented by
the legacy /proc/ hugepages APIs, used for SHM, and
default size when mounting hugetlbfs filesystems.
Defaults to the default architecture's huge page size
if not specified.
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.
dhash_entries= [KNL]
Set number of hash buckets for dentry cache.
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.
disable= [IPV6]
See Documentation/networking/ipv6.txt.
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.
disable_radix [PPC]
Disable RADIX MMU mode on POWER9
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.
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).
disable_ddw [PPC/PSERIES]
Disable Dynamic DMA Window support. Use this if
to workaround buggy firmware.
disable_ipv6= [IPV6]
See Documentation/networking/ipv6.txt.
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.
driver_async_probe= [KNL]
List of driver names to be probed asynchronously.
Format: <driver_name1>,<driver_name2>...
drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
Broken monitors, graphic adapters, KVMs and EDIDless
panels may send no or incorrect EDID data sets.
This parameter allows to specify an EDID data sets
in the /lib/firmware directory that are used instead.
Generic built-in EDID data sets are used, if one of
edid/1024x768.bin, edid/1280x1024.bin,
edid/1680x1050.bin, or edid/1920x1080.bin is given
and no file with the same name exists. Details and
instructions how to build your own EDID data are
available in Documentation/EDID/HOWTO.txt. An EDID
data set will only be used for a particular connector,
if its name and a colon are prepended to the EDID
name. 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]
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.
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.
dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
module.dyndbg[="val"]
Enable debug messages at boot time. See
Documentation/admin-guide/dynamic-debug-howto.rst
for details.
nompx [X86] Disables Intel Memory Protection Extensions.
See Documentation/x86/intel_mpx.txt for more
information about the feature.
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.
[ARM64] The early console is determined by the
stdout-path property in device tree's chosen node,
or determined by the ACPI SPCR table.
[X86] When used with no options the early console is
determined by the ACPI SPCR table.
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.
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.
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.
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.
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.
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.
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.
ar3700_uart,<addr>
Start an early, polled-mode console on the
Armada 3700 serial port at the specified
address. The serial port must already be setup
and configured. Options are not yet supported.
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.
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.
earlyprintk= [X86,SH,ARM,M68k,S390]
earlyprintk=vga
earlyprintk=sclp
earlyprintk=xen
earlyprintk=serial[,ttySn[,baudrate]]
earlyprintk=serial[,0x...[,baudrate]]
earlyprintk=ttySn[,baudrate]
earlyprintk=dbgp[debugController#]
earlyprintk=pciserial[,force],bus:device.function[,baudrate]
earlyprintk=xdbc[xhciController#]
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.
The sclp output can only be used on s390.
The optional "force" to "pciserial" enables use of a
PCI device even when its classcode is not of the
UART class.
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
edd= [EDD]
Format: {"off" | "on" | "skip[mbr]"}
efi= [EFI]
Format: { "old_map", "nochunk", "noruntime", "debug" }
old_map [X86-64]: switch to the old ioremap-based EFI
runtime services mapping. 32-bit still uses this one by
default.
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
debug: enable misc debug output
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.
If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
attribute is added to range 0x100000000-0x180000000 and
0x10a0000000-0x1120000000.
Using this parameter you can do debugging of EFI memmap
related feature. For example, you can do debugging of
Address Range Mirroring feature even if your box
doesn't support it.
efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
that is to be dynamically loaded by Linux. If there are
multiple variables with the same name but with different
vendor GUIDs, all of them will be loaded. See
Documentation/acpi/ssdt-overlays.txt for details.
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.
elevator= [IOSCHED]
Format: { "mq-deadline" | "kyber" | "bfq" }
See Documentation/block/deadline-iosched.txt,
Documentation/block/kyber-iosched.txt and
Documentation/block/bfq-iosched.txt for details.
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.
See Documentation/kdump/kdump.txt for details.
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.
Value can be changed at runtime via /selinux/enforce.
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]
See Documentation/blockdev/floppy.txt.
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.
forcepae [X86-32]
Forcefully enable Physical Address Extension (PAE).
Many Pentium M systems disable PAE but may have a
functionally usable PAE implementation.
Warning: use of this parameter will taint the kernel
and may cause unknown problems.
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.
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)
gamecon.map[2|3]=
[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
support via parallel port (up to 5 devices per port)
Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
See also Documentation/input/devices/joystick-parport.rst
gamma= [HW,DRM]
gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
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.
goldfish [X86] Enable the goldfish android emulator platform.
Don't use this when you are not running on the
android emulator
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
gpio-mockup.gpio_mockup_ranges
[HW] Sets the ranges of gpiochip of for this device.
Format: <start1>,<end1>,<start2>,<end2>...
hardlockup_all_cpu_backtrace=
[KNL] Should the hard-lockup detector generate
backtraces on all cpus.
Format: <integer>
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"
hisax= [HW,ISDN]
See Documentation/isdn/README.HiSax.
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.
hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
On x86-64 and powerpc, this option can be specified
multiple times interleaved with hugepages= to reserve
huge pages of different sizes. Valid pages sizes on
x86-64 are 2M (when the CPU supports "pse") and 1G
(when the CPU supports the "pdpe1gb" cpuinfo flag).
hung_task_panic=
[KNL] Should the hung task detector generate panics.
Format: <integer>
A nonzero value instructs the kernel to panic when a
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.
hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
which allow the hypervisor to 'idle' the
guest on lock contention.
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.
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>
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
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
i8042.unlock [HW] Unlock (ignore) the keylock
i8042.kbdreset [HW] Reset device connected to KBD port
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
See Documentation/ide/ide.txt.
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"
ima_appraise_tcb [IMA]
The builtin appraise policy appraises all files
owned by uid=0.
ima_canonical_fmt [IMA]
Use the canonical format for the binary runtime
measurements, instead of host native format.
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]
The builtin policies to load during IMA setup.
Format: "tcb | appraise_tcb | secure_boot |
fail_securely"
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
all files owned by root. (This is the equivalent
of ima_appraise_tcb.)
The "secure_boot" policy appraises the integrity
of files (eg. kexec kernel image, kernel modules,
firmware, policy, etc) based on file signatures.
The "fail_securely" policy forces file signature
verification failure also on privileged mounted
filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
flag.
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.
ima_template= [IMA]
Select one of defined IMA measurements template formats.
Formats: { "ima" | "ima-ng" | "ima-sig" }
Default: "ima-ng"
ima_template_fmt=
[IMA] Define a custom template format.
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
init_pkru= [x86] Specify the default memory protection keys rights
register contents for all processes. 0x55555554 by
default (disallow access to all but pkey 0). Can
override in debugfs after boot.
inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
Format: <irq>
int_pln_enable [x86] Enable power limit notification interrupt
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.
forcedac [x86_64]
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.
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.
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.
intel_idle.max_cstate= [KNL,HW,ACPI,X86]
0 disables intel_idle and fall back on acpi_idle.
1 to 9 specify maximum depth of C-state.
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
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
iommu= [x86]
off
force
noforce
biomerge
panic
nopanic
merge
nomerge
soft
pt [x86]
nopt [x86]
nobypass [PPC/POWERNV]
Disable IOMMU bypass, using IOMMU for PCI devices.
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.
iommu.passthrough=
[ARM64] Configure DMA to bypass the IOMMU by default.
Format: { "0" | "1" }
0 - Use IOMMU translation for DMA.
1 - Bypass the IOMMU for DMA.
unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
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]
See Documentation/filesystems/nfs/nfsroot.txt.
irqaffinity= [SMP] Set the default irq affinity mask
The argument is a cpu list, as described above.
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.
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.
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.
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>
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.
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.
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".
The format of <cpu-list> is described above.
iucv= [HW,NET]
ivrs_ioapic [HW,X86_64]
Provide an override to the IOAPIC-ID<->DEVICE-ID
mapping provided in the IVRS ACPI table. For
example, to map IOAPIC-ID decimal 10 to
PCI device 00:14.0 write the parameter as:
ivrs_ioapic[10]=00:14.0
ivrs_hpet [HW,X86_64]
Provide an override to the HPET-ID<->DEVICE-ID
mapping provided in the IVRS ACPI table. For
example, to map HPET-ID decimal 0 to
PCI device 00:14.0 write the parameter as:
ivrs_hpet[0]=00:14.0
ivrs_acpihid [HW,X86_64]
Provide an override to the ACPI-HID:UID<->DEVICE-ID
mapping provided in the IVRS ACPI table. For
example, to map UART-HID:UID AMD0020:0 to
PCI device 00:14.5 write the parameter as:
ivrs_acpihid[00:14.5]=AMD0020:0
js= [HW,JOY] Analog joystick
See Documentation/input/joydev/joystick.rst.
nokaslr [KNL]
When CONFIG_RANDOMIZE_BASE is set, this disables
kernel and module base offset ASLR (Address Space
Layout Randomization).
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.
keepinitrd [HW,ARM]
kernelcore= [KNL,X86,IA-64,PPC]
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
zone if it does not.
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"
option is specified, mirrored (reliable) memory is used
for non-movable allocations and remaining memory is used
for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
are exclusive, so you cannot specify multiple forms.
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]
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.
kpti= [ARM64] Control page table isolation of user
and kernel address spaces.
Default: enabled on cores which need mitigation.
0: force disabled
1: force enabled
kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
Default is 0 (don't ignore, but inject #GP)
kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
Default is false (don't support).
kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
KVM MMU at runtime.
Default is 0 (off)
kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
Default is 1 (enabled)
kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
for all guests.
Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
kvm-arm.vgic_v3_group0_trap=
[KVM,ARM] Trap guest accesses to GICv3 group-0
system registers
kvm-arm.vgic_v3_group1_trap=
[KVM,ARM] Trap guest accesses to GICv3 group-1
system registers
kvm-arm.vgic_v3_common_trap=
[KVM,ARM] Trap guest accesses to GICv3 common
system registers
kvm-arm.vgic_v4_enable=
[KVM,ARM] Allow use of GICv4 for direct injection of
LPIs.
kvm-intel.ept= [KVM,Intel] Disable extended page tables
(virtualized MMU) support on capable Intel chips.
Default is 1 (enabled)
kvm-intel.emulate_invalid_guest_state=
[KVM,Intel] Enable emulation of invalid guest states
Default is 0 (disabled)
kvm-intel.flexpriority=
[KVM,Intel] Disable FlexPriority feature (TPR shadow).
Default is 1 (enabled)
kvm-intel.nested=
[KVM,Intel] Enable VMX nesting (nVMX).
Default is 0 (disabled)
kvm-intel.unrestricted_guest=
[KVM,Intel] Disable unrestricted guest feature
(virtualized real and unpaged mode) on capable
Intel chips. Default is 1 (enabled)
kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
CVE-2018-3620.
Valid arguments: never, cond, always
always: L1D cache flush on every VMENTER.
cond: Flush L1D on VMENTER only when the code between
VMEXIT and VMENTER can leak host memory.
never: Disables the mitigation
Default is cond (do L1 cache flush in specific instances)
kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
feature (tagged TLBs) on capable Intel chips.
Default is 1 (enabled)
l1tf= [X86] Control mitigation of the L1TF vulnerability on
affected CPUs
The kernel PTE inversion protection is unconditionally
enabled and cannot be disabled.
full
Provides all available mitigations for the
L1TF vulnerability. Disables SMT and
enables all mitigations in the
hypervisors, i.e. unconditional L1D flush.
SMT control and L1D flush control via the
sysfs interface is still possible after
boot. Hypervisors will issue a warning
when the first VM is started in a
potentially insecure configuration,
i.e. SMT enabled or L1D flush disabled.
full,force
Same as 'full', but disables SMT and L1D
flush runtime control. Implies the
'nosmt=force' command line option.
(i.e. sysfs control of SMT is disabled.)
flush
Leaves SMT enabled and enables the default
hypervisor mitigation, i.e. conditional
L1D flush.
SMT control and L1D flush control via the
sysfs interface is still possible after
boot. Hypervisors will issue a warning
when the first VM is started in a
potentially insecure configuration,
i.e. SMT enabled or L1D flush disabled.
flush,nosmt
Disables SMT and enables the default
hypervisor mitigation.
SMT control and L1D flush control via the
sysfs interface is still possible after
boot. Hypervisors will issue a warning
when the first VM is started in a
potentially insecure configuration,
i.e. SMT enabled or L1D flush disabled.
flush,nowarn
Same as 'flush', but hypervisors will not
warn when a VM is started in a potentially
insecure configuration.
off
Disables hypervisor mitigations and doesn't
emit any warnings.
It also drops the swap size and available
RAM limit restriction on both hypervisor and
bare metal.
Default is 'flush'.
For details see: Documentation/admin-guide/l1tf.rst
l2cr= [PPC]
l3cr= [PPC]
lapic [X86-32,APIC] Enable the local APIC even if BIOS
disabled it.
lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
value for LAPIC timer one-shot implementation. Default
back to the programmable timer unit in the LAPIC.
lapic_timer_c2_ok [X86,APIC] trust the local apic timer
in C2 power state.
libata.dma= [LIBATA] DMA control
libata.dma=0 Disable all PATA and SATA DMA
libata.dma=1 PATA and SATA Disk DMA only
libata.dma=2 ATAPI (CDROM) DMA only
libata.dma=4 Compact Flash DMA only
Combinations also work, so libata.dma=3 enables DMA
for disks and CDROMs, but not CFs.
libata.ignore_hpa= [LIBATA] Ignore HPA limit
libata.ignore_hpa=0 keep BIOS limits (default)
libata.ignore_hpa=1 ignore limits, using full disk
libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
when set.
Format: <int>
libata.force= [LIBATA] Force configurations. The format is comma
separated list of "[ID:]VAL" where ID is
PORT[.DEVICE]. PORT and DEVICE are decimal numbers
matching port, link or device. Basically, it matches
the ATA ID string printed on console by libata. If
the whole ID part is omitted, the last PORT and DEVICE
values are used. If ID hasn't been specified yet, the
configuration applies to all ports, links and devices.
If only DEVICE is omitted, the parameter applies to
the port and all links and devices behind it. DEVICE
number of 0 either selects the first device or the
first fan-out link behind PMP device. It does not
select the host link. DEVICE number of 15 selects the
host link and device attached to it.
The VAL specifies the configuration to force. As long
as there's no ambiguity shortcut notation is allowed.
For example, both 1.5 and 1.5G would work for 1.5Gbps.
The following configurations can be forced.
* Cable type: 40c, 80c, short40c, unk, ign or sata.
Any ID with matching PORT is used.
* SATA link speed limit: 1.5Gbps or 3.0Gbps.
* Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
udma[/][16,25,33,44,66,100,133] notation is also
allowed.
* [no]ncq: Turn on or off NCQ.
* [no]ncqtrim: Turn off queued DSM TRIM.
* nohrst, nosrst, norst: suppress hard, soft
and both resets.
* rstonce: only attempt one reset during
hot-unplug link recovery
* dump_id: dump IDENTIFY data.
* atapi_dmadir: Enable ATAPI DMADIR bridge support
* disable: Disable this device.
If there are multiple matching configurations changing
the same attribute, the last one is used.
memblock=debug [KNL] Enable memblock debug messages.
load_ramdisk= [RAM] List of ramdisks to load from floppy
See Documentation/blockdev/ramdisk.txt.
lockd.nlm_grace_period=P [NFS] Assign grace period.
Format: <integer>
lockd.nlm_tcpport=N [NFS] Assign TCP port.
Format: <integer>
lockd.nlm_timeout=T [NFS] Assign timeout value.
Format: <integer>
lockd.nlm_udpport=M [NFS] Assign UDP port.
Format: <integer>
locktorture.nreaders_stress= [KNL]
Set the number of locking read-acquisition kthreads.
Defaults to being automatically set based on the
number of online CPUs.
locktorture.nwriters_stress= [KNL]
Set the number of locking write-acquisition kthreads.
locktorture.onoff_holdoff= [KNL]
Set time (s) after boot for CPU-hotplug testing.
locktorture.onoff_interval= [KNL]
Set time (s) between CPU-hotplug operations, or
zero to disable CPU-hotplug testing.
locktorture.shuffle_interval= [KNL]
Set task-shuffle interval (jiffies). Shuffling
tasks allows some CPUs to go into dyntick-idle
mode during the locktorture test.
locktorture.shutdown_secs= [KNL]
Set time (s) after boot system shutdown. This
is useful for hands-off automated testing.
locktorture.stat_interval= [KNL]
Time (s) between statistics printk()s.
locktorture.stutter= [KNL]
Time (s) to stutter testing, for example,
specifying five seconds causes the test to run for
five seconds, wait for five seconds, and so on.
This tests the locking primitive's ability to
transition abruptly to and from idle.
locktorture.torture_type= [KNL]
Specify the locking implementation to test.
locktorture.verbose= [KNL]
Enable additional printk() statements.
logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
Format: <irq>
loglevel= All Kernel Messages with a loglevel smaller than the
console loglevel will be printed to the console. It can
also be changed with klogd or other programs. The
loglevels are defined as follows:
0 (KERN_EMERG) system is unusable
1 (KERN_ALERT) action must be taken immediately
2 (KERN_CRIT) critical conditions
3 (KERN_ERR) error conditions
4 (KERN_WARNING) warning conditions
5 (KERN_NOTICE) normal but significant condition
6 (KERN_INFO) informational
7 (KERN_DEBUG) debug-level messages
log_buf_len=n[KMG] Sets the size of the printk ring buffer,
in bytes. n must be a power of two and greater
than the minimal size. The minimal size is defined
by LOG_BUF_SHIFT kernel config parameter. There is
also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
that allows to increase the default size depending on
the number of CPUs. See init/Kconfig for more details.
logo.nologo [FB] Disables display of the built-in Linux logo.
This may be used to provide more screen space for
kernel log messages and is useful when debugging
kernel boot problems.
lp=0 [LP] Specify parallel ports to use, e.g,
lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
lp=reset first parallel port). 'lp=0' disables the
lp=auto printer driver. 'lp=reset' (which can be
specified in addition to the ports) causes
attached printers to be reset. Using
lp=port1,port2,... specifies the parallel ports
to associate lp devices with, starting with
lp0. A port specification may be 'none' to skip
that lp device, or a parport name such as
'parport0'. Specifying 'lp=auto' instead of a
port specification list means that device IDs
from each port should be examined, to see if
an IEEE 1284-compliant printer is attached; if
so, the driver will manage that printer.
See also header of drivers/char/lp.c.
lpj=n [KNL]
Sets loops_per_jiffy to given constant, thus avoiding
time-consuming boot-time autodetection (up to 250 ms per
CPU). 0 enables autodetection (default). To determine
the correct value for your kernel, boot with normal
autodetection and see what value is printed. Note that
on SMP systems the preset will be applied to all CPUs,
which is likely to cause problems if your CPUs need
significantly divergent settings. An incorrect value
will cause delays in the kernel to be wrong, leading to
unpredictable I/O errors and other breakage. Although
unlikely, in the extreme case this might damage your
hardware.
ltpc= [NET]
Format: <io>,<irq>,<dma>
lsm.debug [SECURITY] Enable LSM initialization debugging output.
lsm=lsm1,...,lsmN
[SECURITY] Choose order of LSM initialization. This
overrides CONFIG_LSM, and the "security=" parameter.
machvec= [IA-64] Force the use of a particular machine-vector
(machvec) in a generic kernel.
Example: machvec=hpzx1_swiotlb
machtype= [Loongson] Share the same kernel image file between different
yeeloong laptop.
Example: machtype=lemote-yeeloong-2f-7inch
max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
than or equal to this physical address is ignored.
maxcpus= [SMP] Maximum number of processors that an SMP kernel
will bring up during bootup. maxcpus=n : n >= 0 limits
the kernel to bring up 'n' processors. Surely after
bootup you can bring up the other plugged cpu by executing
"echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
only takes effect during system bootup.
While n=0 is a special case, it is equivalent to "nosmp",
which also disables the IO APIC.
max_loop= [LOOP] The number of loop block devices that get
(loop.max_loop) unconditionally pre-created at init time. The default
number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
of statically allocating a predefined number, loop
devices can be requested on-demand with the
/dev/loop-control interface.
mce [X86-32] Machine Check Exception
mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
md= [HW] RAID subsystems devices and level
See Documentation/admin-guide/md.rst.
mdacon= [MDA]
Format: <first>,<last>
Specifies range of consoles to be captured by the MDA.
mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
Amount of memory to be used when the kernel is not able
to see the whole system memory or for test.
[X86] Work as limiting max address. Use together
with memmap= to avoid physical address space collisions.
Without memmap= PCI devices could be placed at addresses
belonging to unused RAM.
mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
memory.
memchunk=nn[KMG]
[KNL,SH] Allow user to override the default size for
per-device physically contiguous DMA buffers.
memhp_default_state=online/offline
[KNL] Set the initial state for the memory hotplug
onlining policy. If not specified, the default value is
set according to the
CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
option.
See Documentation/memory-hotplug.txt.
memmap=exactmap [KNL,X86] Enable setting of an exact
E820 memory map, as specified by the user.
Such memmap=exactmap lines can be constructed based on
BIOS output or other requirements. See the memmap=nn@ss
option description.
memmap=nn[KMG]@ss[KMG]
[KNL] Force usage of a specific region of memory.
Region of memory to be used is from ss to ss+nn.
If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
which limits max address to nn[KMG].
Multiple different regions can be specified,
comma delimited.
Example:
memmap=100M@2G,100M#3G,1G!1024G
memmap=nn[KMG]#ss[KMG]
[KNL,ACPI] Mark specific memory as ACPI data.
Region of memory to be marked is from ss to ss+nn.
memmap=nn[KMG]$ss[KMG]
[KNL,ACPI] Mark specific memory as reserved.
Region of memory to be reserved is from ss to ss+nn.
Example: Exclude memory from 0x18690000-0x1869ffff
memmap=64K$0x18690000
or
memmap=0x10000$0x18690000
Some bootloaders may need an escape character before '$',
like Grub2, otherwise '$' and the following number
will be eaten.
memmap=nn[KMG]!ss[KMG]
[KNL,X86] Mark specific memory as protected.
Region of memory to be used, from ss to ss+nn.
The memory region may be marked as e820 type 12 (0xc)
and is NVDIMM or ADR memory.
memmap=<size>%<offset>-<oldtype>+<newtype>
[KNL,ACPI] Convert memory within the specified region
from <oldtype> to <newtype>. If "-<oldtype>" is left
out, the whole region will be marked as <newtype>,
even if previously unavailable. If "+<newtype>" is left
out, matching memory will be removed. Types are
specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3 = ACPI, 12 = PRAM.
memory_corruption_check=0/1 [X86]
Some BIOSes seem to corrupt the first 64k of
memory when doing things like suspend/resume.
Setting this option will scan the memory
looking for corruption. Enabling this will
both detect corruption and prevent the kernel
from using the memory being corrupted.
However, its intended as a diagnostic tool; if
repeatable BIOS-originated corruption always
affects the same memory, you can use memmap=
to prevent the kernel from using that memory.
memory_corruption_check_size=size [X86]
By default it checks for corruption in the low
64k, making this memory unavailable for normal
use. Use this parameter to scan for
corruption in more or less memory.
memory_corruption_check_period=seconds [X86]
By default it checks for corruption every 60
seconds. Use this parameter to check at some
other rate. 0 disables periodic checking.
memtest= [KNL,X86,ARM,PPC] Enable memtest
Format: <integer>
default : 0 <disable>
Specifies the number of memtest passes to be
performed. Each pass selects another test
pattern from a given set of patterns. Memtest
fills the memory with this pattern, validates
memory contents and reserves bad memory
regions that are detected.
mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
Valid arguments: on, off
Default (depends on kernel configuration option):
on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
mem_encrypt=on: Activate SME
mem_encrypt=off: Do not activate SME
Refer to Documentation/x86/amd-memory-encryption.txt
for details on when memory encryption can be activated.
mem_sleep_default= [SUSPEND] Default system suspend mode:
s2idle - Suspend-To-Idle
shallow - Power-On Suspend or equivalent (if supported)
deep - Suspend-To-RAM or equivalent (if supported)
See Documentation/admin-guide/pm/sleep-states.rst.
meye.*= [HW] Set MotionEye Camera parameters
See Documentation/media/v4l-drivers/meye.rst.
mfgpt_irq= [IA-32] Specify the IRQ to use for the
Multi-Function General Purpose Timers on AMD Geode
platforms.
mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
the BIOS has incorrectly applied a workaround. TinyBIOS
version 0.98 is known to be affected, 0.99 fixes the
problem by letting the user disable the workaround.
mga= [HW,DRM]
min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
physical address is ignored.
mini2440= [ARM,HW,KNL]
Format:[0..2][b][c][t]
Default: "0tb"
MINI2440 configuration specification:
0 - The attached screen is the 3.5" TFT
1 - The attached screen is the 7" TFT
2 - The VGA Shield is attached (1024x768)
Leaving out the screen size parameter will not load
the TFT driver, and the framebuffer will be left
unconfigured.
b - Enable backlight. The TFT backlight pin will be
linked to the kernel VESA blanking code and a GPIO
LED. This parameter is not necessary when using the
VGA shield.
c - Enable the s3c camera interface.
t - Reserved for enabling touchscreen support. The
touchscreen support is not enabled in the mainstream
kernel as of 2.6.30, a preliminary port can be found
in the "bleeding edge" mini2440 support kernel at
http://repo.or.cz/w/linux-2.6/mini2440.git
mminit_loglevel=
[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
parameter allows control of the logging verbosity for
the additional memory initialisation checks. A value
of 0 disables mminit logging and a level of 4 will
log everything. Information is printed at KERN_DEBUG
so loglevel=8 may also need to be specified.
module.sig_enforce
[KNL] When CONFIG_MODULE_SIG is set, this means that
modules without (valid) signatures will fail to load.
Note that if CONFIG_MODULE_SIG_FORCE is set, that
is always true, so this option does nothing.
module_blacklist= [KNL] Do not load a comma-separated list of
modules. Useful for debugging problem modules.
mousedev.tap_time=
[MOUSE] Maximum time between finger touching and
leaving touchpad surface for touch to be considered
a tap and be reported as a left button click (for
touchpads working in absolute mode only).
Format: <msecs>
mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
reporting absolute coordinates, such as tablets
mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
reporting absolute coordinates, such as tablets
movablecore= [KNL,X86,IA-64,PPC]
Format: nn[KMGTPE] | nn%
This parameter is the complement to kernelcore=, it
specifies the amount of memory used for migratable
allocations. If both kernelcore and movablecore is
specified, then kernelcore will be at *least* the
specified value but may be more. If movablecore on its
own is specified, the administrator must be careful
that the amount of memory usable for all allocations
is not too small.
movable_node [KNL] Boot-time switch to make hotplugable memory
NUMA nodes to be movable. This means that the memory
of such nodes will be usable only for movable
allocations which rules out almost all kernel
allocations. Use with caution!
MTD_Partition= [MTD]
Format: <name>,<region-number>,<size>,<offset>
MTD_Region= [MTD] Format:
<name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
mtdparts= [MTD]
See drivers/mtd/cmdlinepart.c.
multitce=off [PPC] This parameter disables the use of the pSeries
firmware feature for updating multiple TCE entries
at a time.
onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
boundary - index of last SLC block on Flex-OneNAND.
The remaining blocks are configured as MLC blocks.
lock - Configure if Flex-OneNAND boundary should be locked.
Once locked, the boundary cannot be changed.
1 indicates lock status, 0 indicates unlock status.
mtdset= [ARM]
ARM/S3C2412 JIVE boot control
See arch/arm/mach-s3c2412/mach-jive.c
mtouchusb.raw_coordinates=
[HW] Make the MicroTouch USB driver use raw coordinates
('y', default) or cooked coordinates ('n')
mtrr_chunk_size=nn[KMG] [X86]
used for mtrr cleanup. It is largest continuous chunk
that could hold holes aka. UC entries.
mtrr_gran_size=nn[KMG] [X86]
Used for mtrr cleanup. It is granularity of mtrr block.
Default is 1.
Large value could prevent small alignment from
using up MTRRs.
mtrr_spare_reg_nr=n [X86]
Format: <integer>
Range: 0,7 : spare reg number
Default : 1
Used for mtrr cleanup. It is spare mtrr entries number.
Set to 2 or more if your graphical card needs more.
n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
netdev= [NET] Network devices parameters
Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
Note that mem_start is often overloaded to mean
something different and driver-specific.
This usage is only documented in each driver source
file if at all.
nf_conntrack.acct=
[NETFILTER] Enable connection tracking flow accounting
0 to disable accounting
1 to enable accounting
Default value is 0.
nfsaddrs= [NFS] Deprecated. Use ip= instead.
See Documentation/filesystems/nfs/nfsroot.txt.
nfsroot= [NFS] nfs root filesystem for disk-less boxes.
See Documentation/filesystems/nfs/nfsroot.txt.
nfsrootdebug [NFS] enable nfsroot debugging messages.
See Documentation/filesystems/nfs/nfsroot.txt.
nfs.callback_nr_threads=
[NFSv4] set the total number of threads that the
NFS client will assign to service NFSv4 callback
requests.
nfs.callback_tcpport=
[NFS] set the TCP port on which the NFSv4 callback
channel should listen.
nfs.cache_getent=
[NFS] sets the pathname to the program which is used
to update the NFS client cache entries.
nfs.cache_getent_timeout=
[NFS] sets the timeout after which an attempt to
update a cache entry is deemed to have failed.
nfs.idmap_cache_timeout=
[NFS] set the maximum lifetime for idmapper cache
entries.
nfs.enable_ino64=
[NFS] enable 64-bit inode numbers.
If zero, the NFS client will fake up a 32-bit inode
number for the readdir() and stat() syscalls instead
of returning the full 64-bit number.
The default is to return 64-bit inode numbers.
nfs.max_session_cb_slots=
[NFSv4.1] Sets the maximum number of session
slots the client will assign to the callback
channel. This determines the maximum number of
callbacks the client will process in parallel for
a particular server.
nfs.max_session_slots=
[NFSv4.1] Sets the maximum number of session slots
the client will attempt to negotiate with the server.
This limits the number of simultaneous RPC requests
that the client can send to the NFSv4.1 server.
Note that there is little point in setting this
value higher than the max_tcp_slot_table_limit.
nfs.nfs4_disable_idmapping=
[NFSv4] When set to the default of '1', this option
ensures that both the RPC level authentication
scheme and the NFS level operations agree to use
numeric uids/gids if the mount is using the
'sec=sys' security flavour. In effect it is
disabling idmapping, which can make migration from
legacy NFSv2/v3 systems to NFSv4 easier.
Servers that do not support this mode of operation
will be autodetected by the client, and it will fall
back to using the idmapper.
To turn off this behaviour, set the value to '0'.
nfs.nfs4_unique_id=
[NFS4] Specify an additional fixed unique ident-
ification string that NFSv4 clients can insert into
their nfs_client_id4 string. This is typically a
UUID that is generated at system install time.
nfs.send_implementation_id =
[NFSv4.1] Send client implementation identification
information in exchange_id requests.
If zero, no implementation identification information
will be sent.
The default is to send the implementation identification
information.
nfs.recover_lost_locks =
[NFSv4] Attempt to recover locks that were lost due
to a lease timeout on the server. Please note that
doing this risks data corruption, since there are
no guarantees that the file will remain unchanged
after the locks are lost.
If you want to enable the kernel legacy behaviour of
attempting to recover these locks, then set this
parameter to '1'.
The default parameter value of '0' causes the kernel
not to attempt recovery of lost locks.
nfs4.layoutstats_timer =
[NFSv4.2] Change the rate at which the kernel sends
layoutstats to the pNFS metadata server.
Setting this to value to 0 causes the kernel to use
whatever value is the default set by the layout
driver. A non-zero value sets the minimum interval
in seconds between layoutstats transmissions.
nfsd.nfs4_disable_idmapping=
[NFSv4] When set to the default of '1', the NFSv4
server will return only numeric uids and gids to
clients using auth_sys, and will accept numeric uids
and gids from such clients. This is intended to ease
migration from NFSv2/v3.
nmi_debug= [KNL,SH] Specify one or more actions to take
when a NMI is triggered.
Format: [state][,regs][,debounce][,die]
nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
Format: [panic,][nopanic,][num]
Valid num: 0 or 1
0 - turn hardlockup detector in nmi_watchdog off
1 - turn hardlockup detector in nmi_watchdog on
When panic is specified, panic when an NMI watchdog
timeout occurs (or 'nopanic' to override the opposite
default). To disable both hard and soft lockup detectors,
please see 'nowatchdog'.
This is useful when you use a panic=... timeout and
need the box quickly up again.
These settings can be accessed at runtime via
the nmi_watchdog and hardlockup_panic sysctls.
netpoll.carrier_timeout=
[NET] Specifies amount of time (in seconds) that
netpoll should wait for a carrier. By default netpoll
waits 4 seconds.
no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
emulation library even if a 387 maths coprocessor
is present.
no5lvl [X86-64] Disable 5-level paging mode. Forces
kernel to use 4-level paging instead.
no_console_suspend
[HW] Never suspend the console
Disable suspending of consoles during suspend and
hibernate operations. Once disabled, debugging
messages can reach various consoles while the rest
of the system is being put to sleep (ie, while
debugging driver suspend/resume hooks). This may
not work reliably with all consoles, but is known
to work with serial and VGA consoles.
To facilitate more flexible debugging, we also add
console_suspend, a printk module parameter to control
it. Users could use console_suspend (usually
/sys/module/printk/parameters/console_suspend) to
turn on/off it dynamically.
noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
caches in the slab allocator. Saves per-node memory,
but will impact performance.
noalign [KNL,ARM]
noaltinstr [S390] Disables alternative instructions patching
(CPU alternatives feature).
noapic [SMP,APIC] Tells the kernel to not make use of any
IOAPICs that may be present in the system.
noautogroup Disable scheduler automatic task group creation.
nobats [PPC] Do not use BATs for mapping kernel lowmem
on "Classic" PPC cores.
nocache [ARM]
noclflush [BUGS=X86] Don't use the CLFLUSH instruction
nodelayacct [KNL] Disable per-task delay accounting
nodsp [SH] Disable hardware DSP at boot time.
noefi Disable EFI runtime services support.
noexec [IA-64]
noexec [X86]
On X86-32 available only on PAE configured kernels.
noexec=on: enable non-executable mappings (default)
noexec=off: disable non-executable mappings
nosmap [X86]
Disable SMAP (Supervisor Mode Access Prevention)
even if it is supported by processor.
nosmep [X86]
Disable SMEP (Supervisor Mode Execution Prevention)
even if it is supported by processor.
noexec32 [X86-64]
This affects only 32-bit executables.
noexec32=on: enable non-executable mappings (default)
read doesn't imply executable mappings
noexec32=off: disable non-executable mappings
read implies executable mappings
nofpu [MIPS,SH] Disable hardware FPU at boot time.
nofxsr [BUGS=X86-32] Disables x86 floating point extended
register save and restore. The kernel will only save
legacy floating-point registers on task switch.
nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
nosmt [KNL,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
[KNL,x86] Disable symmetric multithreading (SMT).
nosmt=force: Force disable SMT, cannot be undone
via the sysfs control file.
nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
check bypass). With this option data leaks are possible
in the system.
nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
(indirect branch prediction) vulnerability. System may
allow data leaks with this option, which is equivalent
to spectre_v2=off.
nospec_store_bypass_disable
[HW] Disable all mitigations for the Speculative Store Bypass vulnerability
noxsave [BUGS=X86] Disables x86 extended register state save
and restore using xsave. The kernel will fallback to
enabling legacy floating-point and sse state.
noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
register states. The kernel will fall back to use
xsave to save the states. By using this parameter,
performance of saving the states is degraded because
xsave doesn't support modified optimization while
xsaveopt supports it on xsaveopt enabled systems.
noxsaves [X86] Disables xsaves and xrstors used in saving and
restoring x86 extended register state in compacted
form of xsave area. The kernel will fall back to use
xsaveopt and xrstor to save and restore the states
in standard form of xsave area. By using this
parameter, xsave area per process might occupy more
memory on xsaves enabled systems.
nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
wfi(ARM) instruction doesn't work correctly and not to
use it. This is also useful when using JTAG debugger.
no_file_caps Tells the kernel not to honor file capabilities. The
only way then for a file to be executed with privilege
is to be setuid root or executed by root.
nohalt [IA-64] Tells the kernel not to use the power saving
function PAL_HALT_LIGHT when idle. This increases
power-consumption. On the positive side, it reduces
interrupt wake-up latency, which may improve performance
in certain environments such as networked servers or
real-time systems.
nohibernate [HIBERNATION] Disable hibernation and resume.
nohz= [KNL] Boottime enable/disable dynamic ticks
Valid arguments: on, off
Default: on
nohz_full= [KNL,BOOT,SMP,ISOL]
The argument is a cpu list, as described above.
In kernels built with CONFIG_NO_HZ_FULL=y, set
the specified list of CPUs whose tick will be stopped
whenever possible. The boot CPU will be forced outside
the range to maintain the timekeeping. Any CPUs
in this list will have their RCU callbacks offloaded,
just as if they had also been called out in the
rcu_nocbs= boot parameter.
noiotrap [SH] Disables trapped I/O port accesses.
noirqdebug [X86-32] Disables the code which attempts to detect and
disable unhandled interrupt sources.
no_timer_check [X86,APIC] Disables the code which tests for
broken timer IRQ sources.
noisapnp [ISAPNP] Disables ISA PnP code.
noinitrd [RAM] Tells the kernel not to load any configured
initial RAM disk.
nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
remapping.
[Deprecated - use intremap=off]
nointroute [IA-64]
noinvpcid [X86] Disable the INVPCID cpu feature.
nojitter [IA-64] Disables jitter checking for ITC timers.
no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
fault handling.
no-vmw-sched-clock
[X86,PV_OPS] Disable paravirtualized VMware scheduler
clock and use the default one.
no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
steal time is computed, but won't influence scheduler
behaviour
nolapic [X86-32,APIC] Do not enable or use the local APIC.
nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
noltlbs [PPC] Do not use large page/tlb entries for kernel
lowmem mapping on PPC40x and PPC8xx
nomca [IA-64] Disable machine check abort handling
nomce [X86-32] Disable Machine Check Exception
nomfgpt [X86-32] Disable Multi-Function General Purpose
Timer usage (for AMD Geode machines).
nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
shutdown the other cpus. Instead use the REBOOT_VECTOR
irq.
nomodule Disable module load
nopat [X86] Disable PAT (page attribute table extension of
pagetables) support.
nopcid [X86-64] Disable the PCID cpu feature.
norandmaps Don't use address space randomization. Equivalent to
echo 0 > /proc/sys/kernel/randomize_va_space
noreplace-smp [X86-32,SMP] Don't replace SMP instructions
with UP alternatives
nordrand [X86] Disable kernel use of the RDRAND and
RDSEED instructions even if they are supported
by the processor. RDRAND and RDSEED are still
available to user space applications.
noresume [SWSUSP] Disables resume and restores original swap
space.
no-scroll [VGA] Disables scrollback.
This is required for the Braillex ib80-piezo Braille
reader made by F.H. Papenmeier (Germany).
nosbagart [IA-64]
nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
and disable the IO APIC. legacy for "maxcpus=0".
nosoftlockup [KNL] Disable the soft-lockup detector.
nosync [HW,M68K] Disables sync negotiation for all devices.
nowatchdog [KNL] Disable both lockup detectors, i.e.
soft-lockup and NMI watchdog (hard-lockup).
nowb [ARM]
nox2apic [X86-64,APIC] Do not enable x2APIC mode.
cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
Some features depend on CPU0. Known dependencies are:
1. Resume from suspend/hibernate depends on CPU0.
Suspend/hibernate will fail if CPU0 is offline and you
need to online CPU0 before suspend/hibernate.
2. PIC interrupts also depend on CPU0. CPU0 can't be
removed if a PIC interrupt is detected.
It's said poweroff/reboot may depend on CPU0 on some
machines although I haven't seen such issues so far
after CPU0 is offline on a few tested machines.
If the dependencies are under your control, you can
turn on cpu0_hotplug.
nps_mtm_hs_ctr= [KNL,ARC]
This parameter sets the maximum duration, in
cycles, each HW thread of the CTOP can run
without interruptions, before HW switches it.
The actual maximum duration is 16 times this
parameter's value.
Format: integer between 1 and 255
Default: 255
nptcg= [IA-64] Override max number of concurrent global TLB
purges which is reported from either PAL_VM_SUMMARY or
SAL PALO.
nr_cpus= [SMP] Maximum number of processors that an SMP kernel
could support. nr_cpus=n : n >= 1 limits the kernel to
support 'n' processors. It could be larger than the
number of already plugged CPU during bootup, later in
runtime you can physically add extra cpu until it reaches
n. So during boot up some boot time memory for per-cpu
variables need be pre-allocated for later physical cpu
hot plugging.
nr_uarts= [SERIAL] maximum number of UARTs to be registered.
numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
Allowed values are enable and disable
numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
'node', 'default' can be specified
This can be set from sysctl after boot.
See Documentation/sysctl/vm.txt for details.
ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
See Documentation/debugging-via-ohci1394.txt for more
info.
olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
Rather than timing out after 20 ms if an EC
command is not properly ACKed, override the length
of the timeout. We have interrupts disabled while
waiting for the ACK, so if this is set too high
interrupts *may* be lost!
omap_mux= [OMAP] Override bootloader pin multiplexing.
Format: <mux_mode0.mode_name=value>...
For example, to override I2C bus2:
omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
oprofile.timer= [HW]
Use timer interrupt instead of performance counters
oprofile.cpu_type= Force an oprofile cpu type
This might be useful if you have an older oprofile
userland or if you want common events.
Format: { arch_perfmon }
arch_perfmon: [X86] Force use of architectural
perfmon on Intel CPUs instead of the
CPU specific event set.
timer: [X86] Force use of architectural NMI
timer mode (see also oprofile.timer
for generic hr timer mode)
oops=panic Always panic on oopses. Default is to just kill the
process, but there is a small probability of
deadlocking the machine.
This will also cause panics on machine check exceptions.
Useful together with panic=30 to trigger a reboot.
page_owner= [KNL] Boot-time page_owner enabling option.
Storage of the information about who allocated
each page is disabled in default. With this switch,
we can turn it on.
on: enable the feature
page_poison= [KNL] Boot-time parameter changing the state of
poisoning on the buddy allocator, available with
CONFIG_PAGE_POISONING=y.
off: turn off poisoning (default)
on: turn on poisoning
panic= [KNL] Kernel behaviour on panic: delay <timeout>
timeout > 0: seconds before rebooting
timeout = 0: wait forever
timeout < 0: reboot immediately
Format: <timeout>
panic_print= Bitmask for printing system info when panic happens.
User can chose combination of the following bits:
bit 0: print all tasks info
bit 1: print system memory info
bit 2: print timer info
bit 3: print locks info if CONFIG_LOCKDEP is on
bit 4: print ftrace buffer
panic_on_warn panic() instead of WARN(). Useful to cause kdump
on a WARN().
crash_kexec_post_notifiers
Run kdump after running panic-notifiers and dumping
kmsg. This only for the users who doubt kdump always
succeeds in any situation.
Note that this also increases risks of kdump failure,
because some panic notifiers can make the crashed
kernel more unstable.
parkbd.port= [HW] Parallel port number the keyboard adapter is
connected to, default is 0.
Format: <parport#>
parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
0 for XT, 1 for AT (default is AT).
Format: <mode>
parport= [HW,PPT] Specify parallel ports. 0 disables.
Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
Use 'auto' to force the driver to use any
IRQ/DMA settings detected (the default is to
ignore detected IRQ/DMA settings because of
possible conflicts). You can specify the base
address, IRQ, and DMA settings; IRQ and DMA
should be numbers, or 'auto' (for using detected
settings on that particular port), or 'nofifo'
(to avoid using a FIFO even if it is detected).
Parallel ports are assigned in the order they
are specified on the command line, starting
with parport0.
parport_init_mode= [HW,PPT]
Configure VIA parallel port to operate in
a specific mode. This is necessary on Pegasos
computer where firmware has no options for setting
up parallel port mode and sets it to spp.
Currently this function knows 686a and 8231 chips.
Format: [spp|ps2|epp|ecp|ecpepp]
pause_on_oops=
Halt all CPUs after the first oops has been printed for
the specified number of seconds. This is to be used if
your oopses keep scrolling off the screen.
pcbit= [HW,ISDN]
pcd. [PARIDE]
See header of drivers/block/paride/pcd.c.
See also Documentation/blockdev/paride.txt.
pci=option[,option...] [PCI] various PCI subsystem options.
Some options herein operate on a specific device
or a set of devices (<pci_dev>). These are
specified in one of the following formats:
[<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
pci:<vendor>:<device>[:<subvendor>:<subdevice>]
Note: the first format specifies a PCI
bus/device/function address which may change
if new hardware is inserted, if motherboard
firmware changes, or due to changes caused
by other kernel parameters. If the
domain is left unspecified, it is
taken to be zero. Optionally, a path
to a device through multiple device/function
addresses can be specified after the base
address (this is more robust against
renumbering issues). The second format
selects devices using IDs from the
configuration space which may match multiple
devices in the system.
earlydump dump PCI config space before the kernel
changes anything
off [X86] don't probe for the PCI bus
bios [X86-32] force use of PCI BIOS, don't access
the hardware directly. Use this if your machine
has a non-standard PCI host bridge.
nobios [X86-32] disallow use of PCI BIOS, only direct
hardware access methods are allowed. Use this
if you experience crashes upon bootup and you
suspect they are caused by the BIOS.
conf1 [X86] Force use of PCI Configuration Access
Mechanism 1 (config address in IO port 0xCF8,
data in IO port 0xCFC, both 32-bit).
conf2 [X86] Force use of PCI Configuration Access
Mechanism 2 (IO port 0xCF8 is an 8-bit port for
the function, IO port 0xCFA, also 8-bit, sets
bus number. The config space is then accessed
through ports 0xC000-0xCFFF).
See http://wiki.osdev.org/PCI for more info
on the configuration access mechanisms.
noaer [PCIE] If the PCIEAER kernel config parameter is
enabled, this kernel boot option can be used to
disable the use of PCIE advanced error reporting.
nodomains [PCI] Disable support for multiple PCI
root domains (aka PCI segments, in ACPI-speak).
nommconf [X86] Disable use of MMCONFIG for PCI
Configuration
check_enable_amd_mmconf [X86] check for and enable
properly configured MMIO access to PCI
config space on AMD family 10h CPU
nomsi [MSI] If the PCI_MSI kernel config parameter is
enabled, this kernel boot option can be used to
disable the use of MSI interrupts system-wide.
noioapicquirk [APIC] Disable all boot interrupt quirks.
Safety option to keep boot IRQs enabled. This
should never be necessary.
ioapicreroute [APIC] Enable rerouting of boot IRQs to the
primary IO-APIC for bridges that cannot disable
boot IRQs. This fixes a source of spurious IRQs
when the system masks IRQs.
noioapicreroute [APIC] Disable workaround that uses the
boot IRQ equivalent of an IRQ that connects to
a chipset where boot IRQs cannot be disabled.
The opposite of ioapicreroute.
biosirq [X86-32] Use PCI BIOS calls to get the interrupt
routing table. These calls are known to be buggy
on several machines and they hang the machine
when used, but on other computers it's the only
way to get the interrupt routing table. Try
this option if the kernel is unable to allocate
IRQs or discover secondary PCI buses on your
motherboard.
rom [X86] Assign address space to expansion ROMs.
Use with caution as certain devices share
address decoders between ROMs and other
resources.
norom [X86] Do not assign address space to
expansion ROMs that do not already have
BIOS assigned address ranges.
nobar [X86] Do not assign address space to the
BARs that weren't assigned by the BIOS.
irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
assigned automatically to PCI devices. You can
make the kernel exclude IRQs of your ISA cards
this way.
pirqaddr=0xAAAAA [X86] Specify the physical address
of the PIRQ table (normally generated
by the BIOS) if it is outside the
F0000h-100000h range.
lastbus=N [X86] Scan all buses thru bus #N. Can be
useful if the kernel is unable to find your
secondary buses and you want to tell it
explicitly which ones they are.
assign-busses [X86] Always assign all PCI bus
numbers ourselves, overriding
whatever the firmware may have done.
usepirqmask [X86] Honor the possible IRQ mask stored
in the BIOS $PIR table. This is needed on
some systems with broken BIOSes, notably
some HP Pavilion N5400 and Omnibook XE3
notebooks. This will have no effect if ACPI
IRQ routing is enabled.
noacpi [X86] Do not use ACPI for IRQ routing
or for PCI scanning.
use_crs [X86] Use PCI host bridge window information
from ACPI. On BIOSes from 2008 or later, this
is enabled by default. If you need to use this,
please report a bug.
nocrs [X86] Ignore PCI host bridge windows from ACPI.
If you need to use this, please report a bug.
routeirq Do IRQ routing for all PCI devices.
This is normally done in pci_enable_device(),
so this option is a temporary workaround
for broken drivers that don't call it.
skip_isa_align [X86] do not align io start addr, so can
handle more pci cards
noearly [X86] Don't do any early type 1 scanning.
This might help on some broken boards which
machine check when some devices' config space
is read. But various workarounds are disabled
and some IOMMU drivers will not work.
bfsort Sort PCI devices into breadth-first order.
This sorting is done to get a device
order compatible with older (<= 2.4) kernels.
nobfsort Don't sort PCI devices into breadth-first order.
pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
tuning and use the BIOS-configured MPS defaults.
pcie_bus_safe Set every device's MPS to the largest value
supported by all devices below the root complex.
pcie_bus_perf Set device MPS to the largest allowable MPS
based on its parent bus. Also set MRRS (Max
Read Request Size) to the largest supported
value (no larger than the MPS that the device
or bus can support) for best performance.
pcie_bus_peer2peer Set every device's MPS to 128B, which
every device is guaranteed to support. This
configuration allows peer-to-peer DMA between
any pair of devices, possibly at the cost of
reduced performance. This also guarantees
that hot-added devices will work.
cbiosize=nn[KMG] The fixed amount of bus space which is
reserved for the CardBus bridge's IO window.
The default value is 256 bytes.
cbmemsize=nn[KMG] The fixed amount of bus space which is
reserved for the CardBus bridge's memory
window. The default value is 64 megabytes.
resource_alignment=
Format:
[<order of align>@]<pci_dev>[; ...]
Specifies alignment and device to reassign
aligned memory resources. How to
specify the device is described above.
If <order of align> is not specified,
PAGE_SIZE is used as alignment.
PCI-PCI bridge can be specified, if resource
windows need to be expanded.
To specify the alignment for several
instances of a device, the PCI vendor,
device, subvendor, and subdevice may be
specified, e.g., 4096@pci:8086:9c22:103c:198f
ecrc= Enable/disable PCIe ECRC (transaction layer
end-to-end CRC checking).
bios: Use BIOS/firmware settings. This is the
the default.
off: Turn ECRC off
on: Turn ECRC on.
hpiosize=nn[KMG] The fixed amount of bus space which is
reserved for hotplug bridge's IO window.
Default size is 256 bytes.
hpmemsize=nn[KMG] The fixed amount of bus space which is
reserved for hotplug bridge's memory window.
Default size is 2 megabytes.
hpbussize=nn The minimum amount of additional bus numbers
reserved for buses below a hotplug bridge.
Default is 1.
realloc= Enable/disable reallocating PCI bridge resources
if allocations done by BIOS are too small to
accommodate resources required by all child
devices.
off: Turn realloc off
on: Turn realloc on
realloc same as realloc=on
noari do not use PCIe ARI.
noats [PCIE, Intel-IOMMU, AMD-IOMMU]
do not use PCIe ATS (and IOMMU device IOTLB).
pcie_scan_all Scan all possible PCIe devices. Otherwise we
only look for one device below a PCIe downstream
port.
big_root_window Try to add a big 64bit memory window to the PCIe
root complex on AMD CPUs. Some GFX hardware
can resize a BAR to allow access to all VRAM.
Adding the window is slightly risky (it may
conflict with unreported devices), so this
taints the kernel.
disable_acs_redir=<pci_dev>[; ...]
Specify one or more PCI devices (in the format
specified above) separated by semicolons.
Each device specified will have the PCI ACS
redirect capabilities forced off which will
allow P2P traffic between devices through
bridges without forcing it upstream. Note:
this removes isolation between devices and
may put more devices in an IOMMU group.
pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
Management.
off Disable ASPM.
force Enable ASPM even on devices that claim not to support it.
WARNING: Forcing ASPM on may cause system lockups.
pcie_ports= [PCIE] PCIe port services handling:
native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
even if the platform doesn't give the OS permission to
use them. This may cause conflicts if the platform
also tries to use these services.
compat Disable native PCIe services (PME, AER, DPC, PCIe
hotplug).
pcie_port_pm= [PCIE] PCIe port power management handling:
off Disable power management of all PCIe ports
force Forcibly enable power management of all PCIe ports
pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
nomsi Do not use MSI for native PCIe PME signaling (this makes
all PCIe root ports use INTx for all services).
pcmv= [HW,PCMCIA] BadgePAD 4
pd_ignore_unused
[PM]
Keep all power-domains already enabled by bootloader on,
even if no driver has claimed them. This is useful
for debug and development, but should not be
needed on a platform with proper driver support.
pd. [PARIDE]
See Documentation/blockdev/paride.txt.
pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
boot time.
Format: { 0 | 1 }
See arch/parisc/kernel/pdc_chassis.c
percpu_alloc= Select which percpu first chunk allocator to use.
Currently supported values are "embed" and "page".
Archs may support subset or none of the selections.
See comments in mm/percpu.c for details on each
allocator. This parameter is primarily for debugging
and performance comparison.
pf. [PARIDE]
See Documentation/blockdev/paride.txt.
pg. [PARIDE]
See Documentation/blockdev/paride.txt.
pirq= [SMP,APIC] Manual mp-table setup
See Documentation/x86/i386/IO-APIC.txt.
plip= [PPT,NET] Parallel port network link
Format: { parport<nr> | timid | 0 }
See also Documentation/admin-guide/parport.rst.
pmtmr= [X86] Manual setup of pmtmr I/O Port.
Override pmtimer IOPort with a hex value.
e.g. pmtmr=0x508
pnp.debug=1 [PNP]
Enable PNP debug messages (depends on the
CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
via /sys/module/pnp/parameters/debug. We always show
current resource usage; turning this on also shows
possible settings and some assignment information.
pnpacpi= [ACPI]
{ off }
pnpbios= [ISAPNP]
{ on | off | curr | res | no-curr | no-res }
pnp_reserve_irq=
[ISAPNP] Exclude IRQs for the autoconfiguration
pnp_reserve_dma=
[ISAPNP] Exclude DMAs for the autoconfiguration
pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
Ranges are in pairs (I/O port base and size).
pnp_reserve_mem=
[ISAPNP] Exclude memory regions for the
autoconfiguration.
Ranges are in pairs (memory base and size).
ports= [IP_VS_FTP] IPVS ftp helper module
Default is 21.
Up to 8 (IP_VS_APP_MAX_PORTS) ports
may be specified.
Format: <port>,<port>....
powersave=off [PPC] This option disables power saving features.
It specifically disables cpuidle and sets the
platform machine description specific power_save
function to NULL. On Idle the CPU just reduces
execution priority.
ppc_strict_facility_enable
[PPC] This option catches any kernel floating point,
Altivec, VSX and SPE outside of regions specifically
allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
There is some performance impact when enabling this.
ppc_tm= [PPC]
Format: {"off"}
Disable Hardware Transactional Memory
print-fatal-signals=
[KNL] debug: print fatal signals
If enabled, warn about various signal handling
related application anomalies: too many signals,
too many POSIX.1 timers, fatal signals causing a
coredump - etc.
If you hit the warning due to signal overflow,
you might want to try "ulimit -i unlimited".
default: off.
printk.always_kmsg_dump=
Trigger kmsg_dump for cases other than kernel oops or
panics
Format: <bool> (1/Y/y=enable, 0/N/n=disable)
default: disabled
printk.devkmsg={on,off,ratelimit}
Control writing to /dev/kmsg.
on - unlimited logging to /dev/kmsg from userspace
off - logging to /dev/kmsg disabled
ratelimit - ratelimit the logging
Default: ratelimit
printk.time= Show timing data prefixed to each printk message line
Format: <bool> (1/Y/y=enable, 0/N/n=disable)
processor.max_cstate= [HW,ACPI]
Limit processor to maximum C-state
max_cstate=9 overrides any DMI blacklist limit.
processor.nocst [HW,ACPI]
Ignore the _CST method to determine C-states,
instead using the legacy FADT method
profile= [KNL] Enable kernel profiling via /proc/profile
Format: [<profiletype>,]<number>
Param: <profiletype>: "schedule", "sleep", or "kvm"
[defaults to kernel profiling]
Param: "schedule" - profile schedule points.
Param: "sleep" - profile D-state sleeping (millisecs).
Requires CONFIG_SCHEDSTATS
Param: "kvm" - profile VM exits.
Param: <number> - step/bucket size as a power of 2 for
statistical time based profiling.
prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
before loading.
See Documentation/blockdev/ramdisk.txt.
psi= [KNL] Enable or disable pressure stall information
tracking.
Format: <bool>
psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
probe for; one of (bare|imps|exps|lifebook|any).
psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
per second.
psmouse.resetafter= [HW,MOUSE]
Try to reset the device after so many bad packets
(0 = never).
psmouse.resolution=
[HW,MOUSE] Set desired mouse resolution, in dpi.
psmouse.smartscroll=
[HW,MOUSE] Controls Logitech smartscroll autorepeat.
0 = disabled, 1 = enabled (default).
pstore.backend= Specify the name of the pstore backend to use
pt. [PARIDE]
See Documentation/blockdev/paride.txt.
pti= [X86_64] Control Page Table Isolation of user and
kernel address spaces. Disabling this feature
removes hardening, but improves performance of
system calls and interrupts.
on - unconditionally enable
off - unconditionally disable
auto - kernel detects whether your CPU model is
vulnerable to issues that PTI mitigates
Not specifying this option is equivalent to pti=auto.
nopti [X86_64]
Equivalent to pti=off
pty.legacy_count=
[KNL] Number of legacy pty's. Overwrites compiled-in
default number.
quiet [KNL] Disable most log messages
r128= [HW,DRM]
raid= [HW,RAID]
See Documentation/admin-guide/md.rst.
ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
See Documentation/blockdev/ramdisk.txt.
random.trust_cpu={on,off}
[KNL] Enable or disable trusting the use of the
CPU's random number generator (if available) to
fully seed the kernel's CRNG. Default is controlled
by CONFIG_RANDOM_TRUST_CPU.
ras=option[,option,...] [KNL] RAS-specific options
cec_disable [X86]
Disable the Correctable Errors Collector,
see CONFIG_RAS_CEC help text.
rcu_nocbs= [KNL]
The argument is a cpu list, as described above.
In kernels built with CONFIG_RCU_NOCB_CPU=y, set
the specified list of CPUs to be no-callback CPUs.
Invocation of these CPUs' RCU callbacks will be
offloaded to "rcuox/N" kthreads created for that
purpose, where "x" is "p" for RCU-preempt, and
"s" for RCU-sched, and "N" is the CPU number.
This reduces OS jitter on the offloaded CPUs,
which can be useful for HPC and real-time
workloads. It can also improve energy efficiency
for asymmetric multiprocessors.
rcu_nocb_poll [KNL]
Rather than requiring that offloaded CPUs
(specified by rcu_nocbs= above) explicitly
awaken the corresponding "rcuoN" kthreads,
make these kthreads poll for callbacks.
This improves the real-time response for the
offloaded CPUs by relieving them of the need to
wake up the corresponding kthread, but degrades
energy efficiency by requiring that the kthreads
periodically wake up to do the polling.
rcutree.blimit= [KNL]
Set maximum number of finished RCU callbacks to
process in one batch.
rcutree.dump_tree= [KNL]
Dump the structure of the rcu_node combining tree
out at early boot. This is used for diagnostic
purposes, to verify correct tree setup.
rcutree.gp_cleanup_delay= [KNL]
Set the number of jiffies to delay each step of
RCU grace-period cleanup.
rcutree.gp_init_delay= [KNL]
Set the number of jiffies to delay each step of
RCU grace-period initialization.
rcutree.gp_preinit_delay= [KNL]
Set the number of jiffies to delay each step of
RCU grace-period pre-initialization, that is,
the propagation of recent CPU-hotplug changes up
the rcu_node combining tree.
rcutree.rcu_fanout_exact= [KNL]
Disable autobalancing of the rcu_node combining
tree. This is used by rcutorture, and might
possibly be useful for architectures having high
cache-to-cache transfer latencies.
rcutree.rcu_fanout_leaf= [KNL]
Change the number of CPUs assigned to each
leaf rcu_node structure. Useful for very
large systems, which will choose the value 64,
and for NUMA systems with large remote-access
latencies, which will choose a value aligned
with the appropriate hardware boundaries.
rcutree.jiffies_till_first_fqs= [KNL]
Set delay from grace-period initialization to
first attempt to force quiescent states.
Units are jiffies, minimum value is zero,
and maximum value is HZ.
rcutree.jiffies_till_next_fqs= [KNL]
Set delay between subsequent attempts to force
quiescent states. Units are jiffies, minimum
value is one, and maximum value is HZ.
rcutree.jiffies_till_sched_qs= [KNL]
Set required age in jiffies for a
given grace period before RCU starts
soliciting quiescent-state help from
rcu_note_context_switch() and cond_resched().
If not specified, the kernel will calculate
a value based on the most recent settings
of rcutree.jiffies_till_first_fqs
and rcutree.jiffies_till_next_fqs.
This calculated value may be viewed in
rcutree.jiffies_to_sched_qs. Any attempt to set
rcutree.jiffies_to_sched_qs will be cheerfully
overwritten.
rcutree.kthread_prio= [KNL,BOOT]
Set the SCHED_FIFO priority of the RCU per-CPU
kthreads (rcuc/N). This value is also used for
the priority of the RCU boost threads (rcub/N)
and for the RCU grace-period kthreads (rcu_bh,
rcu_preempt, and rcu_sched). If RCU_BOOST is
set, valid values are 1-99 and the default is 1
(the least-favored priority). Otherwise, when
RCU_BOOST is not set, valid values are 0-99 and
the default is zero (non-realtime operation).
rcutree.rcu_nocb_leader_stride= [KNL]
Set the number of NOCB kthread groups, which
defaults to the square root of the number of
CPUs. Larger numbers reduces the wakeup overhead
on the per-CPU grace-period kthreads, but increases
that same overhead on each group's leader.
rcutree.qhimark= [KNL]
Set threshold of queued RCU callbacks beyond which
batch limiting is disabled.
rcutree.qlowmark= [KNL]
Set threshold of queued RCU callbacks below which
batch limiting is re-enabled.
rcutree.rcu_idle_gp_delay= [KNL]
Set wakeup interval for idle CPUs that have
RCU callbacks (RCU_FAST_NO_HZ=y).
rcutree.rcu_idle_lazy_gp_delay= [KNL]
Set wakeup interval for idle CPUs that have
only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
Lazy RCU callbacks are those which RCU can
prove do nothing more than free memory.
rcutree.rcu_kick_kthreads= [KNL]
Cause the grace-period kthread to get an extra
wake_up() if it sleeps three times longer than
it should at force-quiescent-state time.
This wake_up() will be accompanied by a
WARN_ONCE() splat and an ftrace_dump().
rcutree.sysrq_rcu= [KNL]
Commandeer a sysrq key to dump out Tree RCU's
rcu_node tree with an eye towards determining
why a new grace period has not yet started.
rcuperf.gp_async= [KNL]
Measure performance of asynchronous
grace-period primitives such as call_rcu().
rcuperf.gp_async_max= [KNL]
Specify the maximum number of outstanding
callbacks per writer thread. When a writer
thread exceeds this limit, it invokes the
corresponding flavor of rcu_barrier() to allow
previously posted callbacks to drain.
rcuperf.gp_exp= [KNL]
Measure performance of expedited synchronous
grace-period primitives.
rcuperf.holdoff= [KNL]
Set test-start holdoff period. The purpose of
this parameter is to delay the start of the
test until boot completes in order to avoid
interference.
rcuperf.nreaders= [KNL]
Set number of RCU readers. The value -1 selects
N, where N is the number of CPUs. A value
"n" less than -1 selects N-n+1, where N is again
the number of CPUs. For example, -2 selects N
(the number of CPUs), -3 selects N+1, and so on.
A value of "n" less than or equal to -N selects
a single reader.
rcuperf.nwriters= [KNL]
Set number of RCU writers. The values operate
the same as for rcuperf.nreaders.
N, where N is the number of CPUs
rcuperf.perf_type= [KNL]
Specify the RCU implementation to test.
rcuperf.shutdown= [KNL]
Shut the system down after performance tests
complete. This is useful for hands-off automated
testing.
rcuperf.verbose= [KNL]
Enable additional printk() statements.
rcuperf.writer_holdoff= [KNL]
Write-side holdoff between grace periods,
in microseconds. The default of zero says
no holdoff.
rcutorture.fqs_duration= [KNL]
Set duration of force_quiescent_state bursts
in microseconds.
rcutorture.fqs_holdoff= [KNL]
Set holdoff time within force_quiescent_state bursts
in microseconds.
rcutorture.fqs_stutter= [KNL]
Set wait time between force_quiescent_state bursts
in seconds.
rcutorture.fwd_progress= [KNL]
Enable RCU grace-period forward-progress testing
for the types of RCU supporting this notion.
rcutorture.fwd_progress_div= [KNL]
Specify the fraction of a CPU-stall-warning
period to do tight-loop forward-progress testing.
rcutorture.fwd_progress_holdoff= [KNL]
Number of seconds to wait between successive
forward-progress tests.
rcutorture.fwd_progress_need_resched= [KNL]
Enclose cond_resched() calls within checks for
need_resched() during tight-loop forward-progress
testing.
rcutorture.gp_cond= [KNL]
Use conditional/asynchronous update-side
primitives, if available.
rcutorture.gp_exp= [KNL]
Use expedited update-side primitives, if available.
rcutorture.gp_normal= [KNL]
Use normal (non-expedited) asynchronous
update-side primitives, if available.
rcutorture.gp_sync= [KNL]
Use normal (non-expedited) synchronous
update-side primitives, if available. If all
of rcutorture.gp_cond=, rcutorture.gp_exp=,
rcutorture.gp_normal=, and rcutorture.gp_sync=
are zero, rcutorture acts as if is interpreted
they are all non-zero.
rcutorture.n_barrier_cbs= [KNL]
Set callbacks/threads for rcu_barrier() testing.
rcutorture.nfakewriters= [KNL]
Set number of concurrent RCU writers. These just
stress RCU, they don't participate in the actual
test, hence the "fake".
rcutorture.nreaders= [KNL]
Set number of RCU readers. The value -1 selects
N-1, where N is the number of CPUs. A value
"n" less than -1 selects N-n-2, where N is again
the number of CPUs. For example, -2 selects N
(the number of CPUs), -3 selects N+1, and so on.
rcutorture.object_debug= [KNL]
Enable debug-object double-call_rcu() testing.
rcutorture.onoff_holdoff= [KNL]
Set time (s) after boot for CPU-hotplug testing.
rcutorture.onoff_interval= [KNL]
Set time (jiffies) between CPU-hotplug operations,
or zero to disable CPU-hotplug testing.
rcutorture.shuffle_interval= [KNL]
Set task-shuffle interval (s). Shuffling tasks
allows some CPUs to go into dyntick-idle mode
during the rcutorture test.
rcutorture.shutdown_secs= [KNL]
Set time (s) after boot system shutdown. This
is useful for hands-off automated testing.
rcutorture.stall_cpu= [KNL]
Duration of CPU stall (s) to test RCU CPU stall
warnings, zero to disable.
rcutorture.stall_cpu_holdoff= [KNL]
Time to wait (s) after boot before inducing stall.
rcutorture.stall_cpu_irqsoff= [KNL]
Disable interrupts while stalling if set.
rcutorture.stat_interval= [KNL]
Time (s) between statistics printk()s.
rcutorture.stutter= [KNL]
Time (s) to stutter testing, for example, specifying
five seconds causes the test to run for five seconds,
wait for five seconds, and so on. This tests RCU's
ability to transition abruptly to and from idle.
rcutorture.test_boost= [KNL]
Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
"Maybe" means test if the RCU implementation
under test support RCU priority boosting.
rcutorture.test_boost_duration= [KNL]
Duration (s) of each individual boost test.
rcutorture.test_boost_interval= [KNL]
Interval (s) between each boost test.
rcutorture.test_no_idle_hz= [KNL]
Test RCU's dyntick-idle handling. See also the
rcutorture.shuffle_interval parameter.
rcutorture.torture_type= [KNL]
Specify the RCU implementation to test.
rcutorture.verbose= [KNL]
Enable additional printk() statements.
rcupdate.rcu_cpu_stall_suppress= [KNL]
Suppress RCU CPU stall warning messages.
rcupdate.rcu_cpu_stall_timeout= [KNL]
Set timeout for RCU CPU stall warning messages.
rcupdate.rcu_expedited= [KNL]
Use expedited grace-period primitives, for
example, synchronize_rcu_expedited() instead
of synchronize_rcu(). This reduces latency,
but can increase CPU utilization, degrade
real-time latency, and degrade energy efficiency.
No effect on CONFIG_TINY_RCU kernels.
rcupdate.rcu_normal= [KNL]
Use only normal grace-period primitives,
for example, synchronize_rcu() instead of
synchronize_rcu_expedited(). This improves
real-time latency, CPU utilization, and
energy efficiency, but can expose users to
increased grace-period latency. This parameter
overrides rcupdate.rcu_expedited. No effect on
CONFIG_TINY_RCU kernels.
rcupdate.rcu_normal_after_boot= [KNL]
Once boot has completed (that is, after
rcu_end_inkernel_boot() has been invoked), use
only normal grace-period primitives. No effect
on CONFIG_TINY_RCU kernels.
rcupdate.rcu_task_stall_timeout= [KNL]
Set timeout in jiffies for RCU task stall warning
messages. Disable with a value less than or equal
to zero.
rcupdate.rcu_self_test= [KNL]
Run the RCU early boot self tests
rdinit= [KNL]
Format: <full_path>
Run specified binary instead of /init from the ramdisk,
used for early userspace startup. See initrd.
rdt= [HW,X86,RDT]
Turn on/off individual RDT features. List is:
cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
mba.
E.g. to turn on cmt and turn off mba use:
rdt=cmt,!mba
reboot= [KNL]
Format (x86 or x86_64):
[w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
[[,]s[mp]#### \
[[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
[[,]f[orce]
Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
reboot_force is either force or not specified,
reboot_cpu is s[mp]#### with #### being the processor
to be used for rebooting.
relax_domain_level=
[KNL, SMP] Set scheduler's default relax_domain_level.
See Documentation/cgroup-v1/cpusets.txt.
reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
Format: <base1>,<size1>[,<base2>,<size2>,...]
Reserve I/O ports or memory so the kernel won't use
them. If <base> is less than 0x10000, the region
is assumed to be I/O ports; otherwise it is memory.
reservetop= [X86-32]
Format: nn[KMG]
Reserves a hole at the top of the kernel virtual
address space.
reservelow= [X86]
Format: nn[K]
Set the amount of memory to reserve for BIOS at
the bottom of the address space.
reset_devices [KNL] Force drivers to reset the underlying device
during initialization.
resume= [SWSUSP]
Specify the partition device for software suspend
Format:
{/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
resume_offset= [SWSUSP]
Specify the offset from the beginning of the partition
given by "resume=" at which the swap header is located,
in <PAGE_SIZE> units (needed only for swap files).
See Documentation/power/swsusp-and-swap-files.txt
resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
read the resume files
resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
Useful for devices that are detected asynchronously
(e.g. USB and MMC devices).
hibernate= [HIBERNATION]
noresume Don't check if there's a hibernation image
present during boot.
nocompress Don't compress/decompress hibernation images.
no Disable hibernation and resume.
protect_image Turn on image protection during restoration
(that will set all pages holding image data
during restoration read-only).
retain_initrd [RAM] Keep initrd memory after extraction
rfkill.default_state=
0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
etc. communication is blocked by default.
1 Unblocked.
rfkill.master_switch_mode=
0 The "airplane mode" button does nothing.
1 The "airplane mode" button toggles between everything
blocked and the previous configuration.
2 The "airplane mode" button toggles between everything
blocked and everything unblocked.
rhash_entries= [KNL,NET]
Set number of hash buckets for route cache
ring3mwait=disable
[KNL] Disable ring 3 MONITOR/MWAIT feature on supported
CPUs.
ro [KNL] Mount root device read-only on boot
rodata= [KNL]
on Mark read-only kernel memory as read-only (default).
off Leave read-only kernel memory writable for debugging.
rockchip.usb_uart
Enable the uart passthrough on the designated usb port
on Rockchip SoCs. When active, the signals of the
debug-uart get routed to the D+ and D- pins of the usb
port and the regular usb controller gets disabled.
root= [KNL] Root filesystem
See name_to_dev_t comment in init/do_mounts.c.
rootdelay= [KNL] Delay (in seconds) to pause before attempting to
mount the root filesystem
rootflags= [KNL] Set root filesystem mount option string
rootfstype= [KNL] Set root filesystem type
rootwait [KNL] Wait (indefinitely) for root device to show up.
Useful for devices that are detected asynchronously
(e.g. USB and MMC devices).
rproc_mem=nn[KMG][@address]
[KNL,ARM,CMA] Remoteproc physical memory block.
Memory area to be used by remote processor image,
managed by CMA.
rw [KNL] Mount root device read-write on boot
S [KNL] Run init in single mode
s390_iommu= [HW,S390]
Set s390 IOTLB flushing mode
strict
With strict flushing every unmap operation will result in
an IOTLB flush. Default is lazy flushing before reuse,
which is faster.
sa1100ir [NET]
See drivers/net/irda/sa1100_ir.c.
sbni= [NET] Granch SBNI12 leased line adapter
sched_debug [KNL] Enables verbose scheduler debug messages.
schedstats= [KNL,X86] Enable or disable scheduled statistics.
Allowed values are enable and disable. This feature
incurs a small amount of overhead in the scheduler
but is useful for debugging and performance tuning.
skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
xtime_lock contention on larger systems, and/or RCU lock
contention on all systems with CONFIG_MAXSMP set.
Format: { "0" | "1" }
0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
1 -- enable.
Note: increases power consumption, thus should only be
enabled if running jitter sensitive (HPC/RT) workloads.
security= [SECURITY] Choose a legacy "major" security module to
enable at boot. This has been deprecated by the
"lsm=" parameter.
selinux= [SELINUX] Disable or enable SELinux at boot time.
Format: { "0" | "1" }
See security/selinux/Kconfig help text.
0 -- disable.
1 -- enable.
Default value is set via kernel config option.
If enabled at boot time, /selinux/disable can be used
later to disable prior to initial policy load.
apparmor= [APPARMOR] Disable or enable AppArmor at boot time
Format: { "0" | "1" }
See security/apparmor/Kconfig help text
0 -- disable.
1 -- enable.
Default value is set via kernel config option.
serialnumber [BUGS=X86-32]
shapers= [NET]
Maximal number of shapers.
simeth= [IA-64]
simscsi=
slram= [HW,MTD]
slab_nomerge [MM]
Disable merging of slabs with similar size. May be
necessary if there is some reason to distinguish
allocs to different slabs, especially in hardened
environments where the risk of heap overflows and
layout control by attackers can usually be
frustrated by disabling merging. This will reduce
most of the exposure of a heap attack to a single
cache (risks via metadata attacks are mostly
unchanged). Debug options disable merging on their
own.
For more information see Documentation/vm/slub.rst.
slab_max_order= [MM, SLAB]
Determines the maximum allowed order for slabs.
A high setting may cause OOMs due to memory
fragmentation. Defaults to 1 for systems with
more than 32MB of RAM, 0 otherwise.
slub_debug[=options[,slabs]] [MM, SLUB]
Enabling slub_debug allows one to determine the
culprit if slab objects become corrupted. Enabling
slub_debug can create guard zones around objects and
may poison objects when not in use. Also tracks the
last alloc / free. For more information see
Documentation/vm/slub.rst.
slub_memcg_sysfs= [MM, SLUB]
Determines whether to enable sysfs directories for
memory cgroup sub-caches. 1 to enable, 0 to disable.
The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
Enabling this can lead to a very high number of debug
directories and files being created under
/sys/kernel/slub.
slub_max_order= [MM, SLUB]
Determines the maximum allowed order for slabs.
A high setting may cause OOMs due to memory
fragmentation. For more information see
Documentation/vm/slub.rst.
slub_min_objects= [MM, SLUB]
The minimum number of objects per slab. SLUB will
increase the slab order up to slub_max_order to
generate a sufficiently large slab able to contain
the number of objects indicated. The higher the number
of objects the smaller the overhead of tracking slabs
and the less frequently locks need to be acquired.
For more information see Documentation/vm/slub.rst.
slub_min_order= [MM, SLUB]
Determines the minimum page order for slabs. Must be
lower than slub_max_order.
For more information see Documentation/vm/slub.rst.
slub_nomerge [MM, SLUB]
Same with slab_nomerge. This is supported for legacy.
See slab_nomerge for more information.
smart2= [HW]
Format: <io1>[,<io2>[,...,<io8>]]
smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
smsc-ircc2.ircc_sir= [HW] SIR base I/O port
smsc-ircc2.ircc_fir= [HW] FIR base I/O port
smsc-ircc2.ircc_irq= [HW] IRQ line
smsc-ircc2.ircc_dma= [HW] DMA channel
smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
0: Toshiba Satellite 1800 (GP data pin select)
1: Fast pin select (default)
2: ATC IRMode
smt [KNL,S390] Set the maximum number of threads (logical
CPUs) to use per physical CPU on systems capable of
symmetric multithreading (SMT). Will be capped to the
actual hardware limit.
Format: <integer>
Default: -1 (no limit)
softlockup_panic=
[KNL] Should the soft-lockup detector generate panics.
Format: <integer>
A nonzero value instructs the soft-lockup detector
to panic the machine when a soft-lockup occurs. This
is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
which is the respective build-time switch to that
functionality.
softlockup_all_cpu_backtrace=
[KNL] Should the soft-lockup detector generate
backtraces on all cpus.
Format: <integer>
sonypi.*= [HW] Sony Programmable I/O Control Device driver
See Documentation/laptops/sonypi.txt
spectre_v2= [X86] Control mitigation of Spectre variant 2
(indirect branch speculation) vulnerability.
The default operation protects the kernel from
user space attacks.
on - unconditionally enable, implies
spectre_v2_user=on
off - unconditionally disable, implies
spectre_v2_user=off
auto - kernel detects whether your CPU model is
vulnerable
Selecting 'on' will, and 'auto' may, choose a
mitigation method at run time according to the
CPU, the available microcode, the setting of the
CONFIG_RETPOLINE configuration option, and the
compiler with which the kernel was built.
Selecting 'on' will also enable the mitigation
against user space to user space task attacks.
Selecting 'off' will disable both the kernel and
the user space protections.
Specific mitigations can also be selected manually:
retpoline - replace indirect branches
retpoline,generic - google's original retpoline
retpoline,amd - AMD-specific minimal thunk
Not specifying this option is equivalent to
spectre_v2=auto.
spectre_v2_user=
[X86] Control mitigation of Spectre variant 2
(indirect branch speculation) vulnerability between
user space tasks
on - Unconditionally enable mitigations. Is
enforced by spectre_v2=on
off - Unconditionally disable mitigations. Is
enforced by spectre_v2=off
prctl - Indirect branch speculation is enabled,
but mitigation can be enabled via prctl
per thread. The mitigation control state
is inherited on fork.
prctl,ibpb
- Like "prctl" above, but only STIBP is
controlled per thread. IBPB is issued
always when switching between different user
space processes.
seccomp
- Same as "prctl" above, but all seccomp
threads will enable the mitigation unless
they explicitly opt out.
seccomp,ibpb
- Like "seccomp" above, but only STIBP is
controlled per thread. IBPB is issued
always when switching between different
user space processes.
auto - Kernel selects the mitigation depending on
the available CPU features and vulnerability.
Default mitigation:
If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl"
Not specifying this option is equivalent to
spectre_v2_user=auto.
spec_store_bypass_disable=
[HW] Control Speculative Store Bypass (SSB) Disable mitigation
(Speculative Store Bypass vulnerability)
Certain CPUs are vulnerable to an exploit against a
a common industry wide performance optimization known
as "Speculative Store Bypass" in which recent stores
to the same memory location may not be observed by
later loads during speculative execution. The idea
is that such stores are unlikely and that they can
be detected prior to instruction retirement at the
end of a particular speculation execution window.
In vulnerable processors, the speculatively forwarded
store can be used in a cache side channel attack, for
example to read memory to which the attacker does not
directly have access (e.g. inside sandboxed code).
This parameter controls whether the Speculative Store
Bypass optimization is used.
On x86 the options are:
on - Unconditionally disable Speculative Store Bypass
off - Unconditionally enable Speculative Store Bypass
auto - Kernel detects whether the CPU model contains an
implementation of Speculative Store Bypass and
picks the most appropriate mitigation. If the
CPU is not vulnerable, "off" is selected. If the
CPU is vulnerable the default mitigation is
architecture and Kconfig dependent. See below.
prctl - Control Speculative Store Bypass per thread
via prctl. Speculative Store Bypass is enabled
for a process by default. The state of the control
is inherited on fork.
seccomp - Same as "prctl" above, but all seccomp threads
will disable SSB unless they explicitly opt out.
Default mitigations:
X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
On powerpc the options are:
on,auto - On Power8 and Power9 insert a store-forwarding
barrier on kernel entry and exit. On Power7
perform a software flush on kernel entry and
exit.
off - No action.
Not specifying this option is equivalent to
spec_store_bypass_disable=auto.
spia_io_base= [HW,MTD]
spia_fio_base=
spia_pedr=
spia_peddr=
srcutree.counter_wrap_check [KNL]
Specifies how frequently to check for
grace-period sequence counter wrap for the
srcu_data structure's ->srcu_gp_seq_needed field.
The greater the number of bits set in this kernel
parameter, the less frequently counter wrap will
be checked for. Note that the bottom two bits
are ignored.
srcutree.exp_holdoff [KNL]
Specifies how many nanoseconds must elapse
since the end of the last SRCU grace period for
a given srcu_struct until the next normal SRCU
grace period will be considered for automatic
expediting. Set to zero to disable automatic
expediting.
ssbd= [ARM64,HW]
Speculative Store Bypass Disable control
On CPUs that are vulnerable to the Speculative
Store Bypass vulnerability and offer a
firmware based mitigation, this parameter
indicates how the mitigation should be used:
force-on: Unconditionally enable mitigation for
for both kernel and userspace
force-off: Unconditionally disable mitigation for
for both kernel and userspace
kernel: Always enable mitigation in the
kernel, and offer a prctl interface
to allow userspace to register its
interest in being mitigated too.
stack_guard_gap= [MM]
override the default stack gap protection. The value
is in page units and it defines how many pages prior
to (for stacks growing down) resp. after (for stacks
growing up) the main stack are reserved for no other
mapping. Default value is 256 pages.
stacktrace [FTRACE]
Enabled the stack tracer on boot up.
stacktrace_filter=[function-list]
[FTRACE] Limit the functions that the stack tracer
will trace at boot up. function-list is a comma separated
list of functions. This list can be changed at run
time by the stack_trace_filter file in the debugfs
tracing directory. Note, this enables stack tracing
and the stacktrace above is not needed.
sti= [PARISC,HW]
Format: <num>
Set the STI (builtin display/keyboard on the HP-PARISC
machines) console (graphic card) which should be used
as the initial boot-console.
See also comment in drivers/video/console/sticore.c.
sti_font= [HW]
See comment in drivers/video/console/sticore.c.
stifb= [HW]
Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
sunrpc.min_resvport=
sunrpc.max_resvport=
[NFS,SUNRPC]
SunRPC servers often require that client requests
originate from a privileged port (i.e. a port in the
range 0 < portnr < 1024).
An administrator who wishes to reserve some of these
ports for other uses may adjust the range that the
kernel's sunrpc client considers to be privileged
using these two parameters to set the minimum and
maximum port values.
sunrpc.svc_rpc_per_connection_limit=
[NFS,SUNRPC]
Limit the number of requests that the server will
process in parallel from a single connection.
The default value is 0 (no limit).
sunrpc.pool_mode=
[NFS]
Control how the NFS server code allocates CPUs to
service thread pools. Depending on how many NICs
you have and where their interrupts are bound, this
option will affect which CPUs will do NFS serving.
Note: this parameter cannot be changed while the
NFS server is running.
auto the server chooses an appropriate mode
automatically using heuristics
global a single global pool contains all CPUs
percpu one pool for each CPU
pernode one pool for each NUMA node (equivalent
to global on non-NUMA machines)
sunrpc.tcp_slot_table_entries=
sunrpc.udp_slot_table_entries=
[NFS,SUNRPC]
Sets the upper limit on the number of simultaneous
RPC calls that can be sent from the client to a
server. Increasing these values may allow you to
improve throughput, but will also increase the
amount of memory reserved for use by the client.
suspend.pm_test_delay=
[SUSPEND]
Sets the number of seconds to remain in a suspend test
mode before resuming the system (see
/sys/power/pm_test). Only available when CONFIG_PM_DEBUG
is set. Default value is 5.
swapaccount=[0|1]
[KNL] Enable accounting of swap in memory resource
controller if no parameter or 1 is given or disable
it if 0 is given (See Documentation/cgroup-v1/memory.txt)
swiotlb= [ARM,IA-64,PPC,MIPS,X86]
Format: { <int> | force | noforce }
<int> -- Number of I/O TLB slabs
force -- force using of bounce buffers even if they
wouldn't be automatically used by the kernel
noforce -- Never use bounce buffers (for debugging)
switches= [HW,M68k]
sysfs.deprecated=0|1 [KNL]
Enable/disable old style sysfs layout for old udev
on older distributions. When this option is enabled
very new udev will not work anymore. When this option
is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
in older udev will not work anymore.
Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
the kernel configuration.
sysrq_always_enabled
[KNL]
Ignore sysrq setting - this boot parameter will
neutralize any effect of /proc/sys/kernel/sysrq.
Useful for debugging.
tcpmhash_entries= [KNL,NET]
Set the number of tcp_metrics_hash slots.
Default value is 8192 or 16384 depending on total
ram pages. This is used to specify the TCP metrics
cache size. See Documentation/networking/ip-sysctl.txt
"tcp_no_metrics_save" section for more details.
tdfx= [HW,DRM]
test_suspend= [SUSPEND][,N]
Specify "mem" (for Suspend-to-RAM) or "standby" (for
standby suspend) or "freeze" (for suspend type freeze)
as the system sleep state during system startup with
the optional capability to repeat N number of times.
The system is woken from this state using a
wakeup-capable RTC alarm.
thash_entries= [KNL,NET]
Set number of hash buckets for TCP connection
thermal.act= [HW,ACPI]
-1: disable all active trip points in all thermal zones
<degrees C>: override all lowest active trip points
thermal.crt= [HW,ACPI]
-1: disable all critical trip points in all thermal zones
<degrees C>: override all critical trip points
thermal.nocrt= [HW,ACPI]
Set to disable actions on ACPI thermal zone
critical and hot trip points.
thermal.off= [HW,ACPI]
1: disable ACPI thermal control
thermal.psv= [HW,ACPI]
-1: disable all passive trip points
<degrees C>: override all passive trip points to this
value
thermal.tzp= [HW,ACPI]
Specify global default ACPI thermal zone polling rate
<deci-seconds>: poll all this frequency
0: no polling (default)
threadirqs [KNL]
Force threading of all interrupt handlers except those
marked explicitly IRQF_NO_THREAD.
tmem [KNL,XEN]
Enable the Transcendent memory driver if built-in.
tmem.cleancache=0|1 [KNL, XEN]
Default is on (1). Disable the usage of the cleancache
API to send anonymous pages to the hypervisor.
tmem.frontswap=0|1 [KNL, XEN]
Default is on (1). Disable the usage of the frontswap
API to send swap pages to the hypervisor. If disabled
the selfballooning and selfshrinking are force disabled.
tmem.selfballooning=0|1 [KNL, XEN]
Default is on (1). Disable the driving of swap pages
to the hypervisor.
tmem.selfshrinking=0|1 [KNL, XEN]
Default is on (1). Partial swapoff that immediately
transfers pages from Xen hypervisor back to the
kernel based on different criteria.
topology= [S390]
Format: {off | on}
Specify if the kernel should make use of the cpu
topology information if the hardware supports this.
The scheduler will make use of this information and
e.g. base its process migration decisions on it.
Default is on.
topology_updates= [KNL, PPC, NUMA]
Format: {off}
Specify if the kernel should ignore (off)
topology updates sent by the hypervisor to this
LPAR.
tp720= [HW,PS2]
tpm_suspend_pcr=[HW,TPM]
Format: integer pcr id
Specify that at suspend time, the tpm driver
should extend the specified pcr with zeros,
as a workaround for some chips which fail to
flush the last written pcr on TPM_SaveState.
This will guarantee that all the other pcrs
are saved.
trace_buf_size=nn[KMG]
[FTRACE] will set tracing buffer size on each cpu.
trace_event=[event-list]
[FTRACE] Set and start specified trace events in order
to facilitate early boot debugging. The event-list is a
comma separated list of trace events to enable. See
also Documentation/trace/events.rst
trace_options=[option-list]
[FTRACE] Enable or disable tracer options at boot.
The option-list is a comma delimited list of options
that can be enabled or disabled just as if you were
to echo the option name into
/sys/kernel/debug/tracing/trace_options
For example, to enable stacktrace option (to dump the
stack trace of each event), add to the command line:
trace_options=stacktrace
See also Documentation/trace/ftrace.rst "trace options"
section.
tp_printk[FTRACE]
Have the tracepoints sent to printk as well as the
tracing ring buffer. This is useful for early boot up
where the system hangs or reboots and does not give the
option for reading the tracing buffer or performing a
ftrace_dump_on_oops.
To turn off having tracepoints sent to printk,
echo 0 > /proc/sys/kernel/tracepoint_printk
Note, echoing 1 into this file without the
tracepoint_printk kernel cmdline option has no effect.
** CAUTION **
Having tracepoints sent to printk() and activating high
frequency tracepoints such as irq or sched, can cause
the system to live lock.
traceoff_on_warning
[FTRACE] enable this option to disable tracing when a
warning is hit. This turns off "tracing_on". Tracing can
be enabled again by echoing '1' into the "tracing_on"
file located in /sys/kernel/debug/tracing/
This option is useful, as it disables the trace before
the WARNING dump is called, which prevents the trace to
be filled with content caused by the warning output.
This option can also be set at run time via the sysctl
option: kernel/traceoff_on_warning
transparent_hugepage=
[KNL]
Format: [always|madvise|never]
Can be used to control the default behavior of the system
with respect to transparent hugepages.
See Documentation/admin-guide/mm/transhuge.rst
for more details.
tsc= Disable clocksource stability checks for TSC.
Format: <string>
[x86] reliable: mark tsc clocksource as reliable, this
disables clocksource verification at runtime, as well
as the stability checks done at bootup. Used to enable
high-resolution timer mode on older hardware, and in
virtualized environment.
[x86] noirqtime: Do not use TSC to do irq accounting.
Used to run time disable IRQ_TIME_ACCOUNTING on any
platforms where RDTSC is slow and this accounting
can add overhead.
[x86] unstable: mark the TSC clocksource as unstable, this
marks the TSC unconditionally unstable at bootup and
avoids any further wobbles once the TSC watchdog notices.
turbografx.map[2|3]= [HW,JOY]
TurboGraFX parallel port interface
Format:
<port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
See also Documentation/input/devices/joystick-parport.rst
udbg-immortal [PPC] When debugging early kernel crashes that
happen after console_init() and before a proper
console driver takes over, this boot options might
help "seeing" what's going on.
uhash_entries= [KNL,NET]
Set number of hash buckets for UDP/UDP-Lite connections
uhci-hcd.ignore_oc=
[USB] Ignore overcurrent events (default N).
Some badly-designed motherboards generate lots of
bogus events, for ports that aren't wired to
anything. Set this parameter to avoid log spamming.
Note that genuine overcurrent events won't be
reported either.
unknown_nmi_panic
[X86] Cause panic on unknown NMI.
usbcore.authorized_default=
[USB] Default USB device authorization:
(default -1 = authorized except for wireless USB,
0 = not authorized, 1 = authorized, 2 = authorized
if device connected to internal port)
usbcore.autosuspend=
[USB] The autosuspend time delay (in seconds) used
for newly-detected USB devices (default 2). This
is the time required before an idle device will be
autosuspended. Devices for which the delay is set
to a negative value won't be autosuspended at all.
usbcore.usbfs_snoop=
[USB] Set to log all usbfs traffic (default 0 = off).
usbcore.usbfs_snoop_max=
[USB] Maximum number of bytes to snoop in each URB
(default = 65536).
usbcore.blinkenlights=
[USB] Set to cycle leds on hubs (default 0 = off).
usbcore.old_scheme_first=
[USB] Start with the old device initialization
scheme, applies only to low and full-speed devices
(default 0 = off).
usbcore.usbfs_memory_mb=
[USB] Memory limit (in MB) for buffers allocated by
usbfs (default = 16, 0 = max = 2047).
usbcore.use_both_schemes=
[USB] Try the other device initialization scheme
if the first one fails (default 1 = enabled).
usbcore.initial_descriptor_timeout=
[USB] Specifies timeout for the initial 64-byte
USB_REQ_GET_DESCRIPTOR request in milliseconds
(default 5000 = 5.0 seconds).
usbcore.nousb [USB] Disable the USB subsystem
usbcore.quirks=
[USB] A list of quirk entries to augment the built-in
usb core quirk list. List entries are separated by
commas. Each entry has the form
VendorID:ProductID:Flags. The IDs are 4-digit hex
numbers and Flags is a set of letters. Each letter
will change the built-in quirk; setting it if it is
clear and clearing it if it is set. The letters have
the following meanings:
a = USB_QUIRK_STRING_FETCH_255 (string
descriptors must not be fetched using
a 255-byte read);
b = USB_QUIRK_RESET_RESUME (device can't resume
correctly so reset it instead);
c = USB_QUIRK_NO_SET_INTF (device can't handle
Set-Interface requests);
d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
handle its Configuration or Interface
strings);
e = USB_QUIRK_RESET (device can't be reset
(e.g morph devices), don't use reset);
f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
more interface descriptions than the
bNumInterfaces count, and can't handle
talking to these interfaces);
g = USB_QUIRK_DELAY_INIT (device needs a pause
during initialization, after we read
the device descriptor);
h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
high speed and super speed interrupt
endpoints, the USB 2.0 and USB 3.0 spec
require the interval in microframes (1
microframe = 125 microseconds) to be
calculated as interval = 2 ^
(bInterval-1).
Devices with this quirk report their
bInterval as the result of this
calculation instead of the exponent
variable used in the calculation);
i = USB_QUIRK_DEVICE_QUALIFIER (device can't
handle device_qualifier descriptor
requests);
j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
generates spurious wakeup, ignore
remote wakeup capability);
k = USB_QUIRK_NO_LPM (device can't handle Link
Power Management);
l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
(Device reports its bInterval as linear
frames instead of the USB 2.0
calculation);
m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
to be disconnected before suspend to
prevent spurious wakeup);
n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
pause after every control message);
o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
delay after resetting its port);
Example: quirks=0781:5580:bk,0a5c:5834:gij
usbhid.mousepoll=
[USBHID] The interval which mice are to be polled at.
usbhid.jspoll=
[USBHID] The interval which joysticks are to be polled at.
usbhid.kbpoll=
[USBHID] The interval which keyboards are to be polled at.
usb-storage.delay_use=
[UMS] The delay in seconds before a new device is
scanned for Logical Units (default 1).
usb-storage.quirks=
[UMS] A list of quirks entries to supplement or
override the built-in unusual_devs list. List
entries are separated by commas. Each entry has
the form VID:PID:Flags where VID and PID are Vendor
and Product ID values (4-digit hex numbers) and
Flags is a set of characters, each corresponding
to a common usb-storage quirk flag as follows:
a = SANE_SENSE (collect more than 18 bytes
of sense data);
b = BAD_SENSE (don't collect more than 18
bytes of sense data);
c = FIX_CAPACITY (decrease the reported
device capacity by one sector);
d = NO_READ_DISC_INFO (don't use
READ_DISC_INFO command);
e = NO_READ_CAPACITY_16 (don't use
READ_CAPACITY_16 command);
f = NO_REPORT_OPCODES (don't use report opcodes
command, uas only);
g = MAX_SECTORS_240 (don't transfer more than
240 sectors at a time, uas only);
h = CAPACITY_HEURISTICS (decrease the
reported device capacity by one
sector if the number is odd);
i = IGNORE_DEVICE (don't bind to this
device);
j = NO_REPORT_LUNS (don't use report luns
command, uas only);
l = NOT_LOCKABLE (don't try to lock and
unlock ejectable media);
m = MAX_SECTORS_64 (don't transfer more
than 64 sectors = 32 KB at a time);
n = INITIAL_READ10 (force a retry of the
initial READ(10) command);
o = CAPACITY_OK (accept the capacity
reported by the device);
p = WRITE_CACHE (the device cache is ON
by default);
r = IGNORE_RESIDUE (the device reports
bogus residue values);
s = SINGLE_LUN (the device has only one
Logical Unit);
t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
commands, uas only);
u = IGNORE_UAS (don't bind to the uas driver);
w = NO_WP_DETECT (don't test whether the
medium is write-protected).
y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
even if the device claims no cache)
Example: quirks=0419:aaf5:rl,0421:0433:rc
user_debug= [KNL,ARM]
Format: <int>
See arch/arm/Kconfig.debug help text.
1 - undefined instruction events
2 - system calls
4 - invalid data aborts
8 - SIGSEGV faults
16 - SIGBUS faults
Example: user_debug=31
userpte=
[X86] Flags controlling user PTE allocations.
nohigh = do not allocate PTE pages in
HIGHMEM regardless of setting
of CONFIG_HIGHPTE.
vdso= [X86,SH]
On X86_32, this is an alias for vdso32=. Otherwise:
vdso=1: enable VDSO (the default)
vdso=0: disable VDSO mapping
vdso32= [X86] Control the 32-bit vDSO
vdso32=1: enable 32-bit VDSO
vdso32=0 or vdso32=2: disable 32-bit VDSO
See the help text for CONFIG_COMPAT_VDSO for more
details. If CONFIG_COMPAT_VDSO is set, the default is
vdso32=0; otherwise, the default is vdso32=1.
For compatibility with older kernels, vdso32=2 is an
alias for vdso32=0.
Try vdso32=0 if you encounter an error that says:
dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
vector= [IA-64,SMP]
vector=percpu: enable percpu vector domain
video= [FB] Frame buffer configuration
See Documentation/fb/modedb.txt.
video.brightness_switch_enabled= [0,1]
If set to 1, on receiving an ACPI notify event
generated by hotkey, video driver will adjust brightness
level and then send out the event to user space through
the allocated input device; If set to 0, video driver
will only send out the event without touching backlight
brightness level.
default: 1
virtio_mmio.device=
[VMMIO] Memory mapped virtio (platform) device.
<size>@<baseaddr>:<irq>[:<id>]
where:
<size> := size (can use standard suffixes
like K, M and G)
<baseaddr> := physical base address
<irq> := interrupt number (as passed to
request_irq())
<id> := (optional) platform device id
example:
virtio_mmio.device=1K@0x100b0000:48:7
Can be used multiple times for multiple devices.
vga= [BOOT,X86-32] Select a particular video mode
See Documentation/x86/boot.txt and
Documentation/svga.txt.
Use vga=ask for menu.
This is actually a boot loader parameter; the value is
passed to the kernel using a special protocol.
vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
May slow down system boot speed, especially when
enabled on systems with a large amount of memory.
All options are enabled by default, and this
interface is meant to allow for selectively
enabling or disabling specific virtual memory
debugging features.
Available options are:
P Enable page structure init time poisoning
- Disable all of the above options
vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
size of <nn>. This can be used to increase the
minimum size (128MB on x86). It can also be used to
decrease the size and leave more room for directly
mapped kernel RAM.
vmcp_cma=nn[MG] [KNL,S390]
Sets the memory size reserved for contiguous memory
allocations for the vmcp device driver.
vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
Format: <command>
vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
Format: <command>
vmpoff= [KNL,S390] Perform z/VM CP command after power off.
Format: <command>
vsyscall= [X86-64]
Controls the behavior of vsyscalls (i.e. calls to
fixed addresses of 0xffffffffff600x00 from legacy
code). Most statically-linked binaries and older
versions of glibc use these calls. Because these
functions are at fixed addresses, they make nice
targets for exploits that can control RIP.
emulate [default] Vsyscalls turn into traps and are
emulated reasonably safely.
native Vsyscalls are native syscall instructions.
This is a little bit faster than trapping
and makes a few dynamic recompilers work
better than they would in emulation mode.
It also makes exploits much easier to write.
none Vsyscalls don't work at all. This makes
them quite hard to use for exploits but
might break your system.
vt.color= [VT] Default text color.
Format: 0xYX, X = foreground, Y = background.
Default: 0x07 = light gray on black.
vt.cur_default= [VT] Default cursor shape.
Format: 0xCCBBAA, where AA, BB, and CC are the same as
the parameters of the <Esc>[?A;B;Cc escape sequence;
see VGA-softcursor.txt. Default: 2 = underline.
vt.default_blu= [VT]
Format: <blue0>,<blue1>,<blue2>,...,<blue15>
Change the default blue palette of the console.
This is a 16-member array composed of values
ranging from 0-255.
vt.default_grn= [VT]
Format: <green0>,<green1>,<green2>,...,<green15>
Change the default green palette of the console.
This is a 16-member array composed of values
ranging from 0-255.
vt.default_red= [VT]
Format: <red0>,<red1>,<red2>,...,<red15>
Change the default red palette of the console.
This is a 16-member array composed of values
ranging from 0-255.
vt.default_utf8=
[VT]
Format=<0|1>
Set system-wide default UTF-8 mode for all tty's.
Default is 1, i.e. UTF-8 mode is enabled for all
newly opened terminals.
vt.global_cursor_default=
[VT]
Format=<-1|0|1>
Set system-wide default for whether a cursor
is shown on new VTs. Default is -1,
i.e. cursors will be created by default unless
overridden by individual drivers. 0 will hide
cursors, 1 will display them.
vt.italic= [VT] Default color for italic text; 0-15.
Default: 2 = green.
vt.underline= [VT] Default color for underlined text; 0-15.
Default: 3 = cyan.
watchdog timers [HW,WDT] For information on watchdog timers,
see Documentation/watchdog/watchdog-parameters.txt
or other driver-specific files in the
Documentation/watchdog/ directory.
watchdog_thresh=
[KNL]
Set the hard lockup detector stall duration
threshold in seconds. The soft lockup detector
threshold is set to twice the value. A value of 0
disables both lockup detectors. Default is 10
seconds.
workqueue.watchdog_thresh=
If CONFIG_WQ_WATCHDOG is configured, workqueue can
warn stall conditions and dump internal state to
help debugging. 0 disables workqueue stall
detection; otherwise, it's the stall threshold
duration in seconds. The default value is 30 and
it can be updated at runtime by writing to the
corresponding sysfs file.
workqueue.disable_numa
By default, all work items queued to unbound
workqueues are affine to the NUMA nodes they're
issued on, which results in better behavior in
general. If NUMA affinity needs to be disabled for
whatever reason, this option can be used. Note
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
workqueue.power_efficient
Per-cpu workqueues are generally preferred because
they show better performance thanks to cache
locality; unfortunately, per-cpu workqueues tend to
be more power hungry than unbound workqueues.
Enabling this makes the per-cpu workqueues which
were observed to contribute significantly to power
consumption unbound, leading to measurably lower
power usage at the cost of small performance
overhead.
The default value of this parameter is determined by
the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
workqueue.debug_force_rr_cpu
Workqueue used to implicitly guarantee that work
items queued without explicit CPU specified are put
on the local CPU. This guarantee is no longer true
and while local CPU is still preferred work items
may be put on foreign CPUs. This debug option
forces round-robin CPU selection to flush out
usages which depend on the now broken guarantee.
When enabled, memory and cache locality will be
impacted.
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
x86_intel_mid_timer= [X86-32,APBT]
Choose timer option for x86 Intel MID platform.
Two valid options are apbt timer only and lapic timer
plus one apbt timer for broadcast timer.
x86_intel_mid_timer=apbt_only | lapic_and_apbt
xen_512gb_limit [KNL,X86-64,XEN]
Restricts the kernel running paravirtualized under Xen
to use only up to 512 GB of RAM. The reason to do so is
crash analysis tools and Xen tools for doing domain
save/restore/migration must be enabled to handle larger
domains.
xen_emul_unplug= [HW,X86,XEN]
Unplug Xen emulated devices
Format: [unplug0,][unplug1]
ide-disks -- unplug primary master IDE devices
aux-ide-disks -- unplug non-primary-master IDE devices
nics -- unplug network devices
all -- unplug all emulated devices (NICs and IDE disks)
unnecessary -- unplugging emulated devices is
unnecessary even if the host did not respond to
the unplug protocol
never -- do not unplug even if version check succeeds
xen_nopvspin [X86,XEN]
Disables the ticketlock slowpath using Xen PV
optimizations.
xen_nopv [X86]
Disables the PV optimizations forcing the HVM guest to
run as generic HVM guest with no PV drivers.
xen_scrub_pages= [XEN]
Boolean option to control scrubbing pages before giving them back
to Xen, for use by other domains. Can be also changed at runtime
with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
xirc2ps_cs= [NET,PCMCIA]
Format:
<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
xhci-hcd.quirks [USB,KNL]
A hex value specifying bitmask with supplemental xhci
host controller quirks. Meaning of each bit can be
consulted in header drivers/usb/host/xhci.h.
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