parameters may be changed at runtime by the command
"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
-The text in square brackets at the beginning of the description states the
-restrictions on the kernel for the said kernel parameter to be valid. The
-restrictions referred to are that the relevant option is valid if:
+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.
ALSA ALSA sound support is enabled.
APM Advanced Power Management support is enabled.
AX25 Appropriate AX.25 support is enabled.
CD Appropriate CD support is enabled.
- DEVFS devfs support is enabled.
DRM Direct Rendering Management support is enabled.
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
EFI EFI Partitioning (GPT) is enabled
ISAPNP ISA PnP code is enabled.
ISDN Appropriate ISDN support is enabled.
JOY Appropriate joystick support is enabled.
+ LIBATA Libata driver is enabled
LP Printer support is enabled.
LOOP Loopback device support is enabled.
M68k M68k architecture is enabled.
MTD MTD support is enabled.
NET Appropriate network support is enabled.
NUMA NUMA support is enabled.
+ GENERIC_TIME The generic timeofday code is enabled.
NFS Appropriate NFS support is enabled.
OSS OSS sound support is enabled.
+ PV_OPS A paravirtualized kernel
PARIDE The ParIDE subsystem is enabled.
PARISC The PA-RISC architecture is enabled.
PCI PCI bus support is enabled.
Documentation/scsi/.
SELINUX SELinux 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 is enabled.
Do not modify the syntax of boot loader parameters without extreme
need or coordination with <Documentation/i386/boot.txt>.
+There are also arch-specific kernel-parameters not documented here.
+See for example <Documentation/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.
+
+
53c7xx= [HW,SCSI] Amiga SCSI controllers
See header of drivers/scsi/53c7xx.c.
See also Documentation/scsi/ncr53c7xx.txt.
- acpi= [HW,ACPI] Advanced Configuration and Power Interface
+ acpi= [HW,ACPI,X86-64,i386]
+ Advanced Configuration and Power Interface
Format: { force | off | ht | strict | noirq }
force -- enable ACPI if default was off
off -- disable ACPI if default was on
See also Documentation/pm.txt, pci=noacpi
+ acpi_apic_instance= [ACPI, IOAPIC]
+ Format: <int>
+ 2: use 2nd APIC table, if available
+ 1,0: use 1st APIC table
+ default: 0
+
acpi_sleep= [HW,ACPI] Sleep options
Format: { s3_bios, s3_mode }
See Documentation/power/video.txt
acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
Format: <irq>,<irq>...
+ 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] empty param disables _OSI
acpi_serialize [HW,ACPI] force serialization of AML methods
acpi_skip_timer_override [HW,ACPI]
Recognize and ignore IRQ0/pin2 Interrupt Override.
For broken nForce2 BIOS resulting in XT-PIC timer.
+ 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_dbg_layer= [HW,ACPI]
+ acpi.debug_layer= [HW,ACPI]
Format: <int>
Each bit of the <int> indicates an ACPI debug layer,
1: enable, 0: disable. It is useful for boot time
debugging. After system has booted up, it can be set
- via /proc/acpi/debug_layer.
-
- acpi_dbg_level= [HW,ACPI]
+ via /sys/module/acpi/parameters/debug_layer.
+ CONFIG_ACPI_DEBUG must be enabled for this to produce any output.
+ Available bits (add the numbers together) to enable debug output
+ for specific parts of the ACPI subsystem:
+ 0x01 utilities 0x02 hardware 0x04 events 0x08 tables
+ 0x10 namespace 0x20 parser 0x40 dispatcher
+ 0x80 executer 0x100 resources 0x200 acpica debugger
+ 0x400 os services 0x800 acpica disassembler.
+ The number can be in decimal or prefixed with 0x in hex.
+ Warning: Many of these options can produce a lot of
+ output and make your system unusable. Be very careful.
+
+ acpi.debug_level= [HW,ACPI]
Format: <int>
Each bit of the <int> indicates an ACPI debug level,
1: enable, 0: disable. It is useful for boot time
debugging. After system has booted up, it can be set
- via /proc/acpi/debug_level.
+ via /sys/module/acpi/parameters/debug_level.
+ CONFIG_ACPI_DEBUG must be enabled for this to produce any output.
+ Available bits (add the numbers together) to enable different
+ debug output levels of the ACPI subsystem:
+ 0x01 error 0x02 warn 0x04 init 0x08 debug object
+ 0x10 info 0x20 init names 0x40 parse 0x80 load
+ 0x100 dispatch 0x200 execute 0x400 names 0x800 operation region
+ 0x1000 bfield 0x2000 tables 0x4000 values 0x8000 objects
+ 0x10000 resources 0x20000 user requests 0x40000 package.
+ The number can be in decimal or prefixed with 0x in hex.
+ Warning: Many of these options can produce a lot of
+ output and make your system unusable. Be very careful.
+
acpi_fake_ecdt [HW,ACPI] Workaround failure due to BIOS lacking ECDT
override platform specific driver.
See also Documentation/acpi-hotkey.txt.
+ acpi_pm_good [IA-32,X86-64]
+ Override the pmtimer bug detection: force the kernel
+ to assume that this machine's pmtimer latches its value
+ and always returns good values.
+
enable_timer_pin_1 [i386,x86-64]
Enable PIN 1 of APIC timer
Can be useful to work around chipset bugs
autotest [IA64]
- awe= [HW,OSS] AWE32/SB32/AWE64 wave table synth
- Format: <io>,<memsize>,<isapnp>
-
aztcd= [HW,CD] Aztech CD268 CDROM driver
Format: <io>,0x79 (?)
Value can be changed at runtime via
/selinux/checkreqprot.
- clock= [BUGS=IA-32,HW] gettimeofday timesource override.
- Forces specified timesource (if avaliable) to be used
- when calculating gettimeofday(). If specicified
- timesource is not avalible, it defaults to PIT.
+ clock= [BUGS=IA-32, HW] gettimeofday clocksource override.
+ [Deprecated]
+ Forces specified clocksource (if available) to be used
+ when calculating gettimeofday(). If specified
+ clocksource is not available, it defaults to PIT.
Format: { pit | tsc | cyclone | pmtmr }
+ code_bytes [IA32] How many bytes of object code to print in an
+ oops report.
+ Range: 0 - 8192
+ Default: 64
+
disable_8254_timer
enable_8254_timer
[IA32/X86_64] Disable/Enable interrupt 0 timer routing
debug [KNL] Enable kernel debugging (events log level).
+ debug_locks_verbose=
+ [KNL] verbose self-tests
+ Format=<0|1>
+ Print debugging info while doing the locking API
+ self-tests.
+ We default to 0 (no extra messages), setting it to
+ 1 will print _a lot_ more information - normally
+ only useful to kernel developers.
+
decnet= [HW,NET]
Format: <area>[,<node>]
See also Documentation/networking/decnet.txt.
- devfs= [DEVFS]
- See Documentation/filesystems/devfs/boot-options.
-
dhash_entries= [KNL]
Set number of hash buckets for dentry cache.
dtc3181e= [HW,SCSI]
- earlyprintk= [IA-32,X86-64]
+ earlyprintk= [IA-32,X86-64,SH]
earlyprintk=vga
earlyprintk=serial[,ttySn[,baudrate]]
Default value is 0.
Value can be changed at runtime via /selinux/enforce.
- es1370= [HW,OSS]
- Format: <lineout>[,<micbias>]
- See also header of sound/oss/es1370.c.
-
es1371= [HW,OSS]
Format: <spdif>,[<nomix>,[<amplifier>]]
See also header of sound/oss/es1371.c.
eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
Format: <io>[,<irq>]
+ failslab=
+ fail_page_alloc=
+ fail_make_request=[KNL]
+ General fault injection mechanism.
+ Format: <interval>,<probability>,<space>,<times>
+ See also /Documentation/fault-injection/.
+
fd_mcs= [HW,SCSI]
See header of drivers/scsi/fd_mcs.c.
floppy= [HW]
See Documentation/floppy.txt.
- ftape= [HW] Floppy Tape subsystem debugging options.
- See Documentation/ftape.txt.
-
gamecon.map[2|3]=
[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
support via parallel port (up to 5 devices per port)
gscd= [HW,CD]
Format: <io>
- gt96100eth= [NET] MIPS GT96100 Advanced Communication Controller
-
- gus= [HW,OSS]
- Format: <io>,<irq>,<dma>,<dma16>
-
gvp11= [HW,SCSI]
hashdist= [KNL,NUMA] Large hashes allocated during boot
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.
hugepages= [HW,IA-32,IA-64] Maximal number of HugeTLB pages.
- noirqbalance [IA-32,SMP,KNL] Disable kernel irq balancing
-
i8042.direct [HW] Put keyboard port into non-translated mode
- i8042.dumbkbd [HW] Pretend that controlled can only read data from
- keyboard and can not control its state
+ 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
idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed
See Documentation/ide.txt.
- idle= [HW]
- Format: idle=poll or idle=halt
+ idle= [X86]
+ Format: idle=poll or idle=mwait
+ Poll forces a polling idle loop that can slightly improves the performance
+ of waking up a idle CPU, but will use a lot of power and make the system
+ run hot. Not recommended.
+ idle=mwait. On systems which support MONITOR/MWAIT but the kernel chose
+ to not use it because it doesn't save as much power as a normal idle
+ loop use the MONITOR/MWAIT idle loop anyways. Performance should be the same
+ as idle=poll.
+
+ ignore_loglevel [KNL]
+ Ignore loglevel setting - this will print /all/
+ kernel messages to the console. Useful for debugging.
ihash_entries= [KNL]
Set number of hash buckets for inode cache.
ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
See header of drivers/scsi/ips.c.
+ 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>....
+
irqfixup [HW]
When an interrupt is not handled search all handlers
for it. Intended to get systems with badly broken
Format: <RDP>,<reset>,<pci_scan>,<verbosity>
isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
- Format: <cpu number>,...,<cpu number>
+ Format:
+ <cpu number>,...,<cpu number>
+ or
+ <cpu number>-<cpu number> (must be a positive range in ascending order)
+ or a mixture
+ <cpu number>,...,<cpu number>-<cpu number>
This option can be used to specify one or more CPUs
to isolate from the general SMP balancing and scheduling
algorithms. The only way to move a process onto or off
lapic [IA-32,APIC] Enable the local APIC even if BIOS
disabled it.
+ lapic_timer_c2_ok [IA-32,x86-64,APIC] trust the local apic timer in
+ C2 power state.
+
lasi= [HW,SCSI] PARISC LASI driver for the 53c700 chip
Format: addr:<io>,irq:<irq>
(machvec) in a generic kernel.
Example: machvec=hpzx1_swiotlb
- mad16= [HW,OSS] Format:
- <io>,<irq>,<dma>,<dma16>,<mpu_io>,<mpu_irq>,<joystick>
-
- maui= [HW,OSS]
- Format: <io>,<irq>
-
max_loop= [LOOP] Maximum number of loopback devices that can
be mounted
Format: <1-256>
maxcpus= [SMP] Maximum number of processors that an SMP kernel
- should make use of
+ should make use of.
+ Using "nosmp" or "maxcpus=0" will disable SMP
+ entirely (the MPS table probe still happens, though).
+ A command-line option of "maxcpus=<NUM>", where <NUM>
+ is an integer greater than 0, limits the maximum number
+ of CPUs activated in SMP mode to <NUM>.
+ Using "maxcpus=1" on an SMP kernel is the trivial
+ case of an SMP kernel with only one CPU.
max_addr=[KMG] [KNL,BOOT,ia64] All physical memory greater than or
equal to this physical address is ignored.
emulation library even if a 387 maths coprocessor
is present.
+ noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
+ when set.
+ Format: <int>
+
+ noaliencache [MM, NUMA] Disables the allcoation of alien caches in
+ the slab allocator. Saves per-node memory, but will
+ impact performance on real NUMA hardware.
+
noalign [KNL,ARM]
noapic [SMP,APIC] Tells the kernel to not make use of any
nocache [ARM]
+ nodelayacct [KNL] Disable per-task delay accounting
+
nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
noexec [IA-64]
in certain environments such as networked servers or
real-time systems.
+ nohz= [KNL] Boottime enable/disable dynamic ticks
+ Valid arguments: on, off
+ Default: on
+
+ noirqbalance [IA-32,SMP,KNL] Disable kernel irq balancing
+
noirqdebug [IA-32] Disables the code which attempts to detect and
disable unhandled interrupt sources.
+ no_timer_check [IA-32,X86_64,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
nolapic [IA-32,APIC] Do not enable or use the local APIC.
+ nolapic_timer [IA-32,APIC] Do not use the local APIC timer.
+
noltlbs [PPC] Do not use large page/tlb entries for kernel
lowmem mapping on PPC40x.
nomce [IA-32] Machine Check Exception
+ noreplace-paravirt [IA-32,PV_OPS] Don't patch paravirt_ops
+
+ noreplace-smp [IA-32,SMP] Don't replace SMP instructions
+ with UP alternatives
+
noresidual [PPC] Don't use residual data on PReP machines.
noresume [SWSUSP] Disables resume and restores original swap
opl3= [HW,OSS]
Format: <io>
- opl3sa= [HW,OSS]
- Format: <io>,<irq>,<dma>,<dma2>,<mpu_io>,<mpu_irq>
-
opl3sa2= [HW,OSS] Format:
<io>,<irq>,<dma>,<dma2>,<mss_io>,<mpu_io>,<ymode>,<loopback>[,<isapnp>,<multiple]
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.
+ 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.
pcmv= [HW,PCMCIA] BadgePAD 4
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)
processor.max_cstate= [HW,ACPI]
Limit processor to maximum C-state
pt. [PARIDE]
See Documentation/paride.txt.
- quiet= [KNL] Disable log messages
+ quiet [KNL] Disable most log messages
r128= [HW,DRM]
rcu.qlowmark= [KNL,BOOT] Set threshold of queued
RCU callbacks below which batch limiting is re-enabled.
- rcu.rsinterval= [KNL,BOOT,SMP] Set the number of additional
- RCU callbacks to queued before forcing reschedule
- on all cpus.
-
rdinit= [KNL]
Format: <full_path>
Run specified binary instead of /init from the ramdisk,
reboot= [BUGS=IA-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
Format: <reboot_mode>[,<reboot_mode2>[,...]]
- See arch/*/kernel/reboot.c.
+ See arch/*/kernel/reboot.c or arch/*/kernel/process.c
reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
+ reservetop= [IA-32]
+ Format: nn[KMG]
+ Reserves a hole at the top of the kernel virtual
+ address space.
+
+ reset_devices [KNL] Force drivers to reset the underlying device
+ during initialization.
+
resume= [SWSUSP]
Specify the partition device for software suspend
+ 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
+
+ retain_initrd [RAM] Keep initrd memory after extraction
+
rhash_entries= [KNL,NET]
Set number of hash buckets for route cache
scsi_logging= [SCSI]
+ scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are
+ discovered. async scans them in kernel threads,
+ allowing boot to proceed. none ignores them, expecting
+ user space to do the scan.
+
selinux [SELINUX] Disable or enable SELinux at boot time.
Format: { "0" | "1" }
See security/selinux/Kconfig help text.
If enabled at boot time, /selinux/disable can be used
later to disable prior to initial policy load.
+ selinux_compat_net =
+ [SELINUX] Set initial selinux_compat_net flag value.
+ Format: { "0" | "1" }
+ 0 -- use new secmark-based packet controls
+ 1 -- use legacy packet controls
+ Default value is 0 (preferred).
+ Value can be changed at runtime via
+ /selinux/compat_net.
+
serialnumber [BUGS=IA-32]
sg_def_reserved_size= [SCSI]
- sgalaxy= [HW,OSS]
- Format: <io>,<irq>,<dma>,<dma2>,<sgbase>
-
shapers= [NET]
Maximal number of shapers.
smart2= [HW]
Format: <io1>[,<io2>[,...,<io8>]]
+ smp-alt-once [IA-32,SMP] On a hotplug CPU system, only
+ attempt to substitute SMP alternatives once at boot.
+
snd-ad1816a= [HW,ALSA]
snd-ad1848= [HW,ALSA]
snd-ymfpci= [HW,ALSA]
- sonicvibes= [HW,OSS]
- Format: <reverb>
-
sonycd535= [HW,CD]
Format: <io>[,<irq>]
stifb= [HW]
Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
+ sunrpc.pool_mode=
+ [NFS]
+ Control how the NFS server code allocates CPUs to
+ service thread pools. Depending on how many NICs
+ you have and where their interrupts are bound, this
+ option will affect which CPUs will do NFS serving.
+ Note: this parameter cannot be changed while the
+ NFS server is running.
+
+ auto the server chooses an appropriate mode
+ automatically using heuristics
+ global a single global pool contains all CPUs
+ percpu one pool for each CPU
+ pernode one pool for each NUMA node (equivalent
+ to global on non-NUMA machines)
+
swiotlb= [IA-64] Number of I/O TLB slabs
switches= [HW,M68k]
sym53c416= [HW,SCSI]
See header of drivers/scsi/sym53c416.c.
+ sysrq_always_enabled
+ [KNL]
+ Ignore sysrq setting - this boot parameter will
+ neutralize any effect of /proc/sys/kernel/sysrq.
+ Useful for debugging.
+
t128= [HW,SCSI]
See header of drivers/scsi/t128.c.
time Show timing data prefixed to each printk message line
+ clocksource= [GENERIC_TIME] Override the default clocksource
+ Override the default clocksource and use the clocksource
+ with the name specified.
+
tipar.timeout= [HW,PPT]
Set communications timeout in tenths of a second
(default 15).
uart6850= [HW,OSS]
Format: <io>,<irq>
+ uhci-hcd.ignore_oc=
+ [USB] Ignore overcurrent events (default N).
+ Some badly-designed motherboards generate lots of
+ bogus events, for ports that aren't wired to
+ anything. Set this parameter to avoid log spamming.
+ Note that genuine overcurrent events won't be
+ reported either.
+
+ usbcore.autosuspend=
+ [USB] The autosuspend time delay (in seconds) used
+ for newly-detected USB devices (default 2). This
+ is the time required before an idle device will be
+ autosuspended. Devices for which the delay is set
+ to a negative value won't be autosuspended at all.
+
usbhid.mousepoll=
[USBHID] The interval which mice are to be polled at.
+ vdso= [IA-32,SH]
+ vdso=2: enable compat VDSO (default with COMPAT_VDSO)
+ vdso=1: enable VDSO (default)
+ vdso=0: disable VDSO mapping
+
video= [FB] Frame buffer configuration
See Documentation/fb/modedb.txt.
decrease the size and leave more room for directly
mapped kernel RAM.
- vmhalt= [KNL,S390]
+ 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]
+ vmpoff= [KNL,S390] Perform z/VM CP command after power off.
+ Format: <command>
waveartist= [HW,OSS]
Format: <io>,<irq>,<dma>,<dma2>
norandmaps Don't use address space randomization
Equivalent to echo 0 > /proc/sys/kernel/randomize_va_space
+ unwind_debug=N N > 0 will enable dwarf2 unwinder debugging
+ This is useful to get more information why
+ you got a "dwarf2 unwinder stuck"
______________________________________________________________________