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Kernel Parameters
The following is a consolidated list of the kernel parameters as
implemented by the __setup(), core_param() and module_param() macros
and sorted into English Dictionary order (defined as ignoring all
punctuation and sorting digits before letters in a case insensitive
manner), and with descriptions where known.
The kernel parses parameters from the kernel command line up to "--";
if it doesn't recognize a parameter and it doesn't contain a '.', the
parameter gets passed to init: parameters with '=' go into init's
environment, others are passed as command line arguments to init.
Everything after "--" is passed as an argument to init.
Module parameters can be specified in two ways: via the kernel command
line with a module name prefix, or via modprobe, e.g.:
(kernel command line) usbcore.blinkenlights=1
(modprobe command line) modprobe usbcore blinkenlights=1
Parameters for modules which are built into the kernel need to be
specified on the kernel command line. modprobe looks through the
kernel command line (/proc/cmdline) and collects module parameters
when it loads a module, so the kernel command line can be used for
loadable modules too.
Hyphens (dashes) and underscores are equivalent in parameter names, so
log_buf_len=1M print-fatal-signals=1
can also be entered as
log-buf-len=1M print_fatal_signals=1
Double-quotes can be used to protect spaces in values, e.g.:
param="spaces in here"
This document may not be entirely up to date and comprehensive. The command
"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
module. Loadable modules, after being loaded into the running kernel, also
reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
parameters may be changed at runtime by the command
"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
The parameters listed below are only valid if certain kernel build options were
enabled and if respective hardware is present. The text in square brackets at
the beginning of each description states the restrictions within which a
parameter is applicable:
ACPI ACPI support is enabled.
AGP AGP (Accelerated Graphics Port) is enabled.
ALSA ALSA sound support is enabled.
APIC APIC support is enabled.
APM Advanced Power Management support is enabled.
ARM ARM architecture is enabled.
AVR32 AVR32 architecture is enabled.
AX25 Appropriate AX.25 support is enabled.
BLACKFIN Blackfin architecture is enabled.
CLK Common clock infrastructure is enabled.
CMA Contiguous Memory Area support is enabled.
DRM Direct Rendering Management support is enabled.
DYNAMIC_DEBUG Build in debug messages and enable them at runtime
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
EIDE EIDE/ATAPI support is enabled.
EVM Extended Verification Module
FB The frame buffer device is enabled.
FTRACE Function tracing enabled.
GCOV GCOV profiling is enabled.
HW Appropriate hardware is enabled.
IA-64 IA-64 architecture is enabled.
IMA Integrity measurement architecture is enabled.
IOSCHED More than one I/O scheduler is enabled.
IP_PNP IP DHCP, BOOTP, or RARP is enabled.
IPV6 IPv6 support is enabled.
ISAPNP ISA PnP code is enabled.
ISDN Appropriate ISDN support is enabled.
JOY Appropriate joystick support is enabled.
KGDB Kernel debugger support is enabled.
KVM Kernel Virtual Machine support is enabled.
LIBATA Libata driver is enabled
LP Printer support is enabled.
LOOP Loopback device support is enabled.
M68k M68k architecture is enabled.
These options have more detailed description inside of
MDA MDA console support is enabled.
MIPS MIPS architecture is enabled.
MOUSE Appropriate mouse support is enabled.
MSI Message Signaled Interrupts (PCI).
MTD MTD (Memory Technology Device) support is enabled.
NET Appropriate network support is enabled.
NUMA NUMA support is enabled.
NFS Appropriate NFS support is enabled.
OSS OSS sound support is enabled.
PV_OPS A paravirtualized kernel is enabled.
PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
PARISC The PA-RISC architecture is enabled.
PCI PCI bus support is enabled.
PCIE PCI Express support is enabled.
PCMCIA The PCMCIA subsystem is enabled.
PNP Plug & Play support is enabled.
PPC PowerPC architecture is enabled.
PPT Parallel port support is enabled.
PS2 Appropriate PS/2 support is enabled.
RAM RAM disk support is enabled.
S390 S390 architecture is enabled.
SCSI Appropriate SCSI support is enabled.
A lot of drivers have their options described inside
the Documentation/scsi/ sub-directory.
SECURITY Different security models are enabled.
SELINUX SELinux support is enabled.
APPARMOR AppArmor support is enabled.
SERIAL Serial support is enabled.
SH SuperH architecture is enabled.
SMP The kernel is an SMP kernel.
SPARC Sparc architecture is enabled.
SWSUSP Software suspend (hibernation) is enabled.
SUSPEND System suspend states are enabled.
TPM TPM drivers are enabled.
TS Appropriate touchscreen support is enabled.
UMS USB Mass Storage support is enabled.
USB USB support is enabled.
USBHID USB Human Interface Device support is enabled.
V4L Video For Linux support is enabled.
VMMIO Driver for memory mapped virtio devices is enabled.
VGA The VGA console has been enabled.
VT Virtual terminal support is enabled.
WDT Watchdog support is enabled.
XT IBM PC/XT MFM hard disk support is enabled.
X86-32 X86-32, aka i386 architecture is enabled.
X86-64 X86-64 architecture is enabled.
More X86-64 boot options can be found in
Documentation/x86/x86_64/boot-options.txt .
X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
XEN Xen support is enabled
In addition, the following text indicates that the option:
BUGS= Relates to possible processor bugs on the said processor.
KNL Is a kernel start-up parameter.
BOOT Is a boot loader parameter.
Parameters denoted with BOOT are actually interpreted by the boot
loader, and have no meaning to the kernel directly.
Do not modify the syntax of boot loader parameters without extreme
need or coordination with <Documentation/x86/boot.txt>.
There are also arch-specific kernel-parameters not documented here.
See for example <Documentation/x86/x86_64/boot-options.txt>.
Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
a trailing = on the name of any parameter states that that parameter will
be entered as an environment variable, whereas its absence indicates that
it will appear as a kernel argument readable via /proc/cmdline by programs
running once the system is up.
The number of kernel parameters is not limited, but the length of the
complete command line (parameters including spaces etc.) is limited to
a fixed number of characters. This limit depends on the architecture
and is between 256 and 4096 characters. It is defined in the file
./include/asm/setup.h as COMMAND_LINE_SIZE.
Finally, the [KMG] suffix is commonly described after a number of kernel
parameter values. These 'K', 'M', and 'G' letters represent the _binary_
multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
bytes respectively. Such letter suffixes can also be entirely omitted.
acpi= [HW,ACPI,X86]
Advanced Configuration and Power Interface
Format: { force | off | strict | noirq | rsdt }
force -- enable ACPI if default was off
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
See also Documentation/power/runtime_pm.txt, pci=noacpi
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_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]
If set to vendor, prefer vendor specific driver
(e.g. thinkpad_acpi, sony_acpi, etc.) instead
of the ACPI video.ko driver.
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.,
Bits in debug_level correspond to a level in
ACPI_DEBUG_PRINT statements, e.g.,
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:
Enable PCI/PCI interrupt routing info messages:
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_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_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_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
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.
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_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
Format: To spoof as Windows 98: ="Microsoft Windows"
acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
acpi_osi="string1" # add string1
acpi_osi="!string2" # remove string2
acpi_osi=!* # remove all strings
acpi_osi=! # disable all built-in OS vendor
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.
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
1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
'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.
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"'
'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 }
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).
acpi_use_timer_override [HW,ACPI]
Use timer override. For some broken Nvidia NF5 boards
that require a timer override, but don't have HPET
acpi_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_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
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)
See Documentation/sound/alsa/alsa-parameters.txt
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. [HW,JOY] Amiga joystick support
Map of devices attached to JOY0DAT and JOY1DAT
Format: <a>,<b>
See also Documentation/input/joystick.txt [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,X86-32] Advanced Programmable Interrupt Controller
Change the output verbosity whilst booting
Format: { quiet (default) | verbose | debug }
Change the amount of debugging information output
when initialising the APIC and IO-APIC components.
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
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" } (0 = disabled, 1 = enabled)
0 - kernel audit is disabled and can not be enabled
until the next reboot
unset - kernel audit is initialized but disabled and
will be fully enabled by the userspace auditd.
1 - kernel audit is initialized and partially enabled,
storing at most audit_backlog_limit messages in
RAM until it is fully enabled by the userspace
Default: unset
audit_backlog_limit= [KNL] Set the audit queue size limit.
Format: <int> (must be >=0)
Default: 64
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.
bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) Most important insmod options are available as
kernel args too.
bttv.pll= See Documentation/video4linux/bttv/Insmod-options
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.
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
{Currently only "memory" controller deal with this and
cut the overhead, others just disable the usage. So
only cgroup_disable=memory is actually worthy}
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
cio_ignore= [S390]
See Documentation/s390/CommonIO for details.
Keep all clocks 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.
For more information, see Documentation/clk.txt.
clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
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,
[AVR32] avr32
[X86-32] pit,hpet,tsc;
scx200_hrt on Geode; cyclone on IBM x440
[PARISC] cr16
[S390] tod
[SH] SuperH
[SPARC64] tick
[X86-64] hpet,tsc
clearcpuid=BITNUM [X86]
Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeature.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.
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. For more information, see
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.
code_bytes [X86] How many bytes of object code to print
in an oops report.
Range: 0 - 8192
Default: 64
com20020= [HW,NET] ARCnet - COM20020 chipset
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
console= [KNL] Output console device and options.
tty<n> Use the virtual console device <n>.
Use the specified serial port. The options are of
the form "bbbbpnf", where "bbbb" is the baud rate,
"p" is parity ("n", "o", or "e"), "n" is number of
bits, and "f" is flow control ("r" for RTS or
omit it). Default is "9600n8".
See Documentation/serial-console.txt for more
information. See
Documentation/networking/netconsole.txt for an
Start an early, polled-mode console on the 8250/16550
UART at the specified I/O port or MMIO address,
switching to the matching ttyS device later. The
options are the same as for ttyS, above.
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
For now, only VisioBraille is supported.
consoleblank= [KNL] The console blank (screen saver) timeout in
seconds. Defaults to 10*60 = 10mins. A value of 0
disables the blank timer.
[KNL] Change the default value for
See also Documentation/filesystems/proc.txt. [CPU_IDLE]
disable the cpuidle sub-system
cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
[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.
[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.
[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
It will be ignored if crashkernel=X is specified.
[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. Kernel would
try to allocate 72M below 4G automatically.
This one let user to specify own low range under 4G
for second kernel instead.
0: to disable low allocation.
It will be ignored when crashkernel=X,high is not used
or memory reserved is below 4G.
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.[2|3]= [HW,JOY] Multisystem joystick support via parallel port
(one device per port)
Format: <port#>,<type>
See also Documentation/input/joystick-parport.txt
ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
time. See Documentation/dynamic-debug-howto.txt for
details. Deprecated, see dyndbg.
debug [KNL] Enable kernel debugging (events log level).
[KNL] verbose self-tests
Print debugging info while doing the locking API
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
[KNL] Disable object debugging
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.
debugpat [X86] Enable PAT debugging
decnet.addr= [HW,NET]
Format: <area>[,<node>]
See also Documentation/networking/decnet.txt.
[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.
dhash_entries= [KNL]
Set number of hash buckets for dentry cache.
disable= [IPV6]
See Documentation/networking/ipv6.txt.
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.
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.
dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
this option disables the debugging code at boot.
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.
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.
Broken monitors, graphic adapters and KVMs may
send no or incorrect EDID data sets. This parameter
allows to specify an EDID data set in the
/lib/firmware directory that is used instead.
Generic built-in EDID data sets are used, if one of
edid/1024x768.bin, edid/1280x1024.bin,
edid/1680x1050.bin, or edid/1920x1080.bin is given
and no file with the same name exists. Details and
instructions how to build your own EDID data are
available in Documentation/EDID/HOWTO.txt. An EDID
data set will only be used for a particular connector,
if its name and a colon are prepended to the EDID
dscc4.setup= [NET]
dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
Enable debug messages at boot time. See
Documentation/dynamic-debug-howto.txt for details.
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.
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).
The options are the same as for ttyS, above.
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.
smh Use ARM semihosting calls for early console.
earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
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:
You can find the port for a given device in
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.
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
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" }
old_map [X86-64]: switch to the old ioremap-based EFI
runtime services mapping. 32-bit still uses this one by
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.
eisa_irq_edge= [PARISC,HW]
See header of drivers/parisc/eisa.c.
elanfreq= [X86-32]
See comment before function elanfreq_setup() in
elevator= [IOSCHED]
Format: {"cfq" | "deadline" | "noop"}
See Documentation/block/cfq-iosched.txt and
Documentation/block/deadline-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)
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.
General fault injection mechanism.
Format: <interval>,<probability>,<space>,<times>
See also Documentation/fault-injection/.
floppy= [HW]
See Documentation/blockdev/floppy.txt.
[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] will set and start the specified tracer
as early as possible in order to facilitate early
boot debugging.
[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
[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] 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] 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.[2|3]=
[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
support via parallel port (up to 5 devices per port)
Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
See also Documentation/input/joystick-parport.txt
gamma= [HW,DRM]
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.
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 [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
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.
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)
Note that 1GB pages can only be allocated at boot time
using hugepages= and not freed afterwards.
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.
hwthread_map= [METAG] Comma-separated list of Linux cpu id to
hardware thread id mappings.
Format: <cpu>:<hwthread>
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.
i8042.debug [HW] Toggle i8042 debug mode [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
i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
i8042.notimeout [HW] Ignore timeout condition signalled by controller
i8042.reset [HW] Reset the controller during init and cleanup
i8042.unlock [HW] Unlock (ignore) the keylock
i810= [HW,DRM]
i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
indicates that the driver is running on unsupported
i8k.force [HW] Activate i8k driver even if SMM BIOS signature
does not match list of supported models.
[HW] Report power status in /proc/i8k
(disabled by default)
i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
capability is set.
[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-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
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
ihash_entries= [KNL]
Set number of hash buckets for inode cache.
ima_appraise= [IMA] appraise integrity measurements
Format: { "off" | "enforce" | "fix" }
default: "enforce"
ima_appraise_tcb [IMA]
The builtin appraise policy appraises all files
owned by uid=0.
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_tcb [IMA]
Load a policy which meets the needs of the Trusted
Computing Base. This means IMA will measure all
programs exec'd, files mmap'd for exec, and all files
opened for read by uid=0.
ima_template= [IMA]
Select one of defined IMA measurements template formats.
Formats: { "ima" | "ima-ng" }
Default: "ima-ng"
init= [KNL]
Format: <full_path>
Run specified binary instead of /sbin/init as init
initcall_debug [KNL] Trace initcalls as they are executed. Useful
for working out where the kernel is dying during
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
inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
Format: <irq>
int_pln_enable [x86] Enable power limit notification interrupt
Format: { "0" | "1" }
0 -- basic integrity auditing messages. (Default)
1 -- additional integrity auditing messages.
intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
Enable intel iommu driver.
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
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.
intel_idle.max_cstate= [KNL,HW,ACPI,X86]
0 disables intel_idle and fall back on acpi_idle.
1 to 6 specify maximum depth of C-state.
intel_pstate= [X86]
Do not enable intel_pstate as the default
scaling driver for the supported processors
intremap= [X86-64, Intel-IOMMU]
on enable Interrupt Remapping (default)
off disable Interrupt Remapping
nosid disable Source ID checking
BIOS x2APIC opt-out request will be ignored
iomem= Disable strict checking of access to MMIO memory
strict regions from userspace.
iommu= [x86]
pt [x86, IA-64]
io7= [HW] IO7 for Marvel based alpha systems
See comment before marvel_specify_io7 in
io_delay= [X86] I/O delay method
Standard port 0x80 based delay
Alternate port 0xed based delay (needed on some systems)
Simple two microseconds delay
No delay
ip= [IP_PNP]
See Documentation/filesystems/nfs/nfsroot.txt.
ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
See comment before ip2_setup() in
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] Isolate CPUs from the general scheduler.
<cpu number>,...,<cpu number>
<cpu number>-<cpu number>
(must be a positive range in ascending order)
or a mixture
<cpu number>,...,<cpu number>-<cpu number>
This option can be used to specify one or more CPUs
to isolate from the general SMP balancing and scheduling
algorithms. 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".
This option is the preferred way to isolate CPUs. The
alternative -- manually setting the CPU mask of all
tasks in the system -- can cause problems and
suboptimal load balancer performance.
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_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:
js= [HW,JOY] Analog joystick
See Documentation/input/joystick.txt.
kaslr/nokaslr [X86]
Enable/disable kernel and module base offset ASLR
(Address Space Layout Randomization) if built into
the kernel. When CONFIG_HIBERNATION is selected,
kASLR is disabled by default. When kASLR is enabled,
hibernation will be disabled.
keepinitrd [HW,ARM]
kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] 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. The
remaining memory in each node is used for Movable
pages. In the event, a node is too small to have both
kernelcore and Movable pages, kernelcore pages will
take priority and other nodes will have a larger number
of Movable pages. The Movable zone is used for the
allocation of pages that may be reclaimed or moved
by the page migration subsystem. This means that
HugeTLB pages may not be allocated from this zone.
Note that allocations like PTEs-from-HighMem still
use the HighMem zone if it exists, and the Normal
zone if it does not.
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
kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
Valid arguments: 0, 1, 2
kmemcheck=0 (disabled)
kmemcheck=1 (enabled)
kmemcheck=2 (one-shot mode)
Default: 2 (one-shot mode)
kstack=N [X86] Print N words from the kernel stack
in oops dumps.
kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
Default is 0 (don't ignore, but inject #GP)
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-intel.ept= [KVM,Intel] Disable extended page tables
(virtualized MMU) support on capable Intel chips.
Default is 1 (enabled)
[KVM,Intel] Enable emulation of invalid guest states
Default is 0 (disabled)
[KVM,Intel] Disable FlexPriority feature (TPR shadow).
Default is 1 (enabled)
[KVM,Intel] Enable VMX nesting (nVMX).
Default is 0 (disabled)
[KVM,Intel] Disable unrestricted guest feature
(virtualized real and unpaged mode) on capable
Intel chips. Default is 1 (enabled)
kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
feature (tagged TLBs) on capable Intel chips.
Default is 1 (enabled)
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
* [no]ncq: Turn on or off NCQ.
* 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>
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. The default
size is set in the kernel config file.
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
ltpc= [NET]
Format: <io>,<irq>,<dma>
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
should make use of. maxcpus=n : n >= 0 limits the
kernel to using 'n' processors. n=0 is a special case,
it is equivalent to "nosmp", which also disables
the IO APIC.
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/md.txt.
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
[KNL,SH] Allow user to override the default size for
per-device physically contiguous DMA buffers.
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.
[KNL] Force usage of a specific region of memory.
Region of memory to be used is from ss to ss+nn.
[KNL,ACPI] Mark specific memory as ACPI data.
Region of memory to be marked is from ss to ss+nn.
[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
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] 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.
meye.*= [HW] Set MotionEye Camera parameters
See Documentation/video4linux/meye.txt.
mfgpt_irq= [IA-32] Specify the IRQ to use for the
Multi-Function General Purpose Timers on AMD Geode
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]
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
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
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.
[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.
[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=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
is similar to kernelcore except it specifies the
amount of memory used for migratable allocations.
If both kernelcore and movablecore is specified,
then kernelcore will be at *least* the specified
value but may be more. If movablecore on its own
is specified, the administrator must be careful
that the amount of memory usable for all allocations
is not too small.
movable_node [KNL,X86] Boot-time switch to enable the effects
of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
MTD_Partition= [MTD]
Format: <name>,<region-number>,<size>,<offset>
MTD_Region= [MTD] Format:
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
[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.
[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] set the TCP port on which the NFSv4 callback
channel should listen.
[NFS] sets the pathname to the program which is used
to update the NFS client cache entries.
[NFS] sets the timeout after which an attempt to
update a cache entry is deemed to have failed.
[NFS] set the maximum lifetime for idmapper cache
[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.
[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.
[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'.
[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
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.
[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.
[NFS] [OBJLAYOUT] sets the pathname to the program which
is used to automatically discover and login into new
osd-targets. Please see:
Documentation/filesystems/pnfs.txt for more explanations
nmi_debug= [KNL,AVR32,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
0 - turn nmi_watchdog off
When panic is specified, panic when an NMI watchdog
timeout occurs (or 'nopanic' to override the opposite
This is useful when you use a panic=... timeout and
need the box quickly up again.
[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.
[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]
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
nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
nodsp [SH] Disable hardware DSP at boot time.
noefi [X86] 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 [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.
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.
eagerfpu= [X86]
on enable eager fpu restore
off disable eager fpu restore
auto selects the default scheme, which automatically
enables eagerfpu restore for xsaveopt.
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]
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.
The CPUs in this range must also be included in the
rcu_nocbs= set.
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
[Deprecated - use intremap=off]
nointroute [IA-64]
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-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
steal time is computed, but won't influence scheduler
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.
nomca [IA-64] Disable machine check abort handling
nomce [X86-32] 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
nomodule Disable module load
nopat [X86] Disable PAT (page attribute table extension of
pagetables) support.
norandmaps Don't use address space randomization. Equivalent to
echo 0 > /proc/sys/kernel/randomize_va_space
noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
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
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.
notsc [BUGS=X86-32] Disable Time Stamp Counter
nousb [USB] Disable the USB subsystem
nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
nowb [ARM]
nox2apic [X86-64,APIC] Do not enable x2APIC mode.
cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
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.
nptcg= [IA-64] Override max number of concurrent global TLB
purges which is reported from either PAL_VM_SUMMARY or
nr_cpus= [SMP] Maximum number of processors that an SMP kernel
could support. nr_cpus=n : n >= 1 limits the kernel to
supporting 'n' processors. Later in runtime you can not
use hotplug cpu feature to put more cpu back to online.
just like you compile the kernel NR_CPUS=n
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.
one of ['zone', '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
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:
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)
[s390] Force legacy basic mode sampling
(report cpu_type "timer")
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.
See Documentation/sound/oss/oss-parameters.txt
panic= [KNL] Kernel behaviour on panic: delay <timeout>
timeout > 0: seconds before rebooting
timeout = 0: wait forever
timeout < 0: reboot immediately
Format: <timeout>
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]
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:
earlydump [X86] 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
Mechanism 1.
conf2 [X86] Force use of PCI Configuration
Mechanism 2.
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
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
rom [X86] Assign address space to expansion ROMs.
Use with caution as certain devices share
address decoders between ROMs and other
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
firmware [ARM] Do not re-enumerate the bus but instead
just use the configuration from the
bootloader. This is currently used on
IXP2000 systems where the bus has to be
configured a certain way for adjunct CPUs.
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.
[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
Specifies alignment and device to reassign
aligned memory resources.
If <order of align> is not specified,
PAGE_SIZE is used as alignment.
PCI-PCI bridge can be specified, if resource
windows need to be expanded.
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.
realloc= Enable/disable reallocating PCI bridge resources
if allocations done by BIOS are too small to
accommodate resources required by all child
off: Turn realloc off
on: Turn realloc on
realloc same as realloc=on
noari do not use PCIe ARI.
pcie_scan_all Scan all possible PCIe devices. Otherwise we
only look for one device below a PCIe downstream
pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
off Disable ASPM.
force Enable ASPM even on devices that claim not to support it.
WARNING: Forcing ASPM on may cause system lockups.
pcie_hp= [PCIE] PCI Express Hotplug driver options:
nomsi Do not use MSI for PCI Express Native Hotplug (this
makes all PCIe ports use INTx for hotplug services).
pcie_ports= [PCIE] PCIe ports handling:
auto Ask the BIOS whether or not to use native PCIe services
associated with PCIe ports (PME, hot-plug, AER). Use
them only if that is allowed by the BIOS.
native Use native PCIe services associated with PCIe ports
compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
ports driver.
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
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/parport.txt.
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 }
[ISAPNP] Exclude IRQs for the autoconfiguration
[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).
[ISAPNP] Exclude memory regions for the
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>....
[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.
Trigger kmsg_dump for cases other than kernel oops or
Format: <bool> (1/Y/y=enable, 0/N/n=disable)
default: disabled
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: [schedule,]<number>
Param: "schedule" - profile schedule points.
Param: <number> - step/bucket size as a power of 2 for
statistical time based profiling.
Param: "sleep" - profile D-state sleeping (millisecs).
Param: "kvm" - profile VM exits.
prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
before loading.
See Documentation/blockdev/ramdisk.txt.
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).
[HW,MOUSE] Set desired mouse resolution, in dpi.
[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.
[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/md.txt.
ramdisk_blocksize= [RAM]
See Documentation/blockdev/ramdisk.txt.
ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
See Documentation/blockdev/ramdisk.txt.
rcu_nocbs= [KNL]
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 "b" for RCU-bh, "p"
for RCU-preempt, and "s" for RCU-sched, and "N"
is the CPU number. This reduces OS jitter on the
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.rcu_fanout_leaf= [KNL]
Increase the number of CPUs assigned to each
leaf rcu_node structure. Useful for very large
rcutree.jiffies_till_sched_qs= [KNL]
Set required age in jiffies for a
given grace period before RCU starts
soliciting quiescent-state help from
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.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.
rcutorture.fqs_duration= [KNL]
Set duration of force_quiescent_state bursts.
rcutorture.fqs_holdoff= [KNL]
Set holdoff time within force_quiescent_state bursts.
rcutorture.fqs_stutter= [KNL]
Set wait time between force_quiescent_state bursts.
rcutorture.gp_exp= [KNL]
Use expedited update-side primitives.
rcutorture.gp_normal= [KNL]
Use normal (non-expedited) update-side primitives.
If both gp_exp and gp_normal are set, do both.
If neither gp_exp nor gp_normal are set, still
do both.
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.
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 (s) between CPU-hotplug operations, or
zero to disable CPU-hotplug testing.
rcutorture.rcutorture_runnable= [BOOT]
Start rcutorture running at boot time.
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.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_expedited= [KNL]
Use expedited grace-period primitives, for
example, synchronize_rcu_expedited() instead
of synchronize_rcu(). This reduces latency,
but can increase CPU utilization, degrade
real-time latency, and degrade energy efficiency.
rcupdate.rcu_cpu_stall_suppress= [KNL]
Suppress RCU CPU stall warning messages.
rcupdate.rcu_cpu_stall_timeout= [KNL]
Set timeout for RCU CPU stall warning messages.
rdinit= [KNL]
Format: <full_path>
Run specified binary instead of /init from the ramdisk,
used for early userspace startup. See initrd.
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]] \
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.
[KNL, SMP] Set scheduler's default relax_domain_level.
See Documentation/cgroups/cpusets.txt.
[SUSPEND] Use sleep state labeling where the deepest
state available other than hibernation is always "mem".
Format: { "0" | "1" }
0 -- Traditional sleep state labels.
1 -- Relative sleep state labels.
reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
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
{/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.
retain_initrd [RAM] Keep initrd memory after extraction
rhash_entries= [KNL,NET]
Set number of hash buckets for route cache
ro [KNL] Mount root device read-only on boot
root= [KNL] Root filesystem
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).
[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
sa1100ir [NET]
See drivers/net/irda/sa1100_ir.c.
sbni= [NET] Granch SBNI12 leased line adapter
sched_debug [KNL] Enables verbose scheduler debug messages.
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 security module to enable at boot.
If this boot parameter is not specified, only the first
security module asking for security registration will be
loaded. An invalid security module name will be treated
as if no module has been chosen.
selinux= [SELINUX] Disable or enable SELinux at boot time.
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.
show_msr= [x86] show boot-time MSR settings
Format: { <integer> }
Show boot-time (BIOS-initialized) MSR settings.
The parameter means the number of CPUs to show,
for example 1 means boot CPU only.
simeth= [IA-64]
slram= [HW,MTD]
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
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
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.txt.
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.txt.
slub_nomerge [MM, SLUB]
Disable merging of slabs with similar size. May be
necessary if there is some reason to distinguish
allocs to different slabs. Debug options disable
merging on their own.
For more information see Documentation/vm/slub.txt.
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
[KNL] Should the soft-lockup detector generate panics.
Format: <integer>
[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
spia_io_base= [HW,MTD]
stacktrace [FTRACE]
Enabled the stack tracer on boot up.
[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 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.
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)
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.
[KNL] Enable accounting of swap in memory resource
controller if no parameter or 1 is given or disable
it if 0 is given (See Documentation/cgroups/memory.txt)
swiotlb= [ARM,IA-64,PPC,MIPS,X86]
Format: { <int> | force }
<int> -- Number of I/O TLB slabs
force -- force using of bounce buffers even if they
wouldn't be automatically used by the kernel
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.
Ignore sysrq setting - this boot parameter will
neutralize any effect of /proc/sys/kernel/sysrq.
Useful for debugging.
tdfx= [HW,DRM]
test_suspend= [SUSPEND]
Specify "mem" (for Suspend-to-RAM) or "standby" (for
standby suspend) as the system sleep state to briefly
enter during system startup. 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. [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
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.
tp720= [HW,PS2]
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.
[FTRACE] will set tracing buffer size.
[FTRACE] Set and start specified trace events in order
to facilitate early boot debugging.
See also Documentation/trace/events.txt
[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
For example, to enable stacktrace option (to dump the
stack trace of each event), add to the command line:
See also Documentation/trace/ftrace.txt "trace options"
[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
Format: [always|madvise|never]
Can be used to control the default behavior of the system
with respect to transparent hugepages.
See Documentation/vm/transhuge.txt for more details.
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.[2|3]= [HW,JOY]
TurboGraFX parallel port interface
See also Documentation/input/joystick-parport.txt
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
[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.
[X86] Cause panic on unknown NMI.
[USB] Default USB device authorization:
(default -1 = authorized except for wireless USB,
0 = not authorized, 1 = authorized)
[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.
[USB] Set to log all usbfs traffic (default 0 = off).
[USB] Set to cycle leds on hubs (default 0 = off).
[USB] Start with the old device initialization
scheme (default 0 = off).
[USB] Memory limit (in MB) for buffers allocated by
usbfs (default = 16, 0 = max = 2047).
[USB] Try the other device initialization scheme
if the first one fails (default 1 = enabled).
[USB] Specifies timeout for the initial 64-byte
USB_REQ_GET_DESCRIPTOR request in milliseconds
(default 5000 = 5.0 seconds).
[USBHID] The interval which mice are to be polled at.
[UMS] The delay in seconds before a new device is
scanned for Logical Units (default 5).
[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);
h = CAPACITY_HEURISTICS (decrease the
reported device capacity by one
sector if the number is odd);
i = IGNORE_DEVICE (don't bind to this
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);
w = NO_WP_DETECT (don't test whether the
medium is write-protected).
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
[X86] Flags controlling user PTE allocations.
nohigh = do not allocate PTE pages in
HIGHMEM regardless of setting
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
[VMMIO] Memory mapped virtio (platform) device.
<size> := size (can use standard suffixes
like K, M and G)
<baseaddr> := physical base address
<irq> := interrupt number (as passed to
<id> := (optional) platform device id
Can be used multiple times for multiple devices.
vga= [BOOT,X86-32] Select a particular video mode
See Documentation/x86/boot.txt and
Use vga=ask for menu.
This is actually a boot loader parameter; the value is
passed to the kernel using a special protocol.
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.
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.
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.
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.
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/.
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
The default value of this parameter is determined by
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_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
xirc2ps_cs= [NET,PCMCIA]
Add more DRM drivers.