10 boot time parameters you should know about the Linux kernel
The Linux kernel accepts boot time parameters as it starts to boot system. This is used to inform kernel about various hardware parameter. You need boot time parameters:
* Troubleshoot system
* Hardware parameters that the kernel would not able to determine on its own
* Force kernel to override the default hardware parameters in order to increase performance
* Password and other recovery operations
The kernel command line syntax
name=value1,value2,value3…
Where,
- name : Keyword name, for example, init, ro, boot etc
Ten common Boot time parameters
init
This sets the initial command to be executed by the kernel. Default is to use /sbin/init, which is the parent of all processes.
To boot system without password pass /bin/bash or /bin/sh as argument to initinit=/bin/bash
single
The most common argument that is passed to the init process is the word 'single' which instructs init to boot the computer in single user mode, and not launch all the usual daemons
root=/dev/device
This argument tells the kernel what device (hard disk, floppy disk) to be used as the root filesystem while booting. For example following boot parameter use /dev/sda1 as the root file system:root=/dev/sda1
If you copy entire partition from /dev/sda1 to /dev/sdb1 then useroot=/dev/sdb1
ro
This argument tells the kernel to mount root file system as read-only. This is done so that fsck program can check and repair a Linux file system. Please note that you should never ever run fsck on read/write file system.
rw
This argument tells the kernel to mount root file system as read and write mode.
panic=SECOND
Specify kernel behavior on panic. By default, the kernel will not reboot after a panic, but this option will cause a kernel reboot after N seconds. For example following boot parameter will force to reboot Linux after 10 secondspanic=10
maxcpus=NUMBER
Specify maximum number of processors that an SMP kernel should make use of. For example if you have four cpus and would like to use 2 CPU then pass 2 as a number to maxcpus (useful to test different software performances and configurations).maxcpus=2
debug
Enable kernel debugging. This option is useful for kernel hackers and developers who wish to troubleshoot problem
selinux [0|1]
Disable or enable SELinux at boot time.
- Value 0 : Disable selinux
- Value 1 : Enable selinux
raid=/dev/mdN
This argument tells kernel howto assembly of RAID arrays at boot time. Please note that When md is compiled into the kernel (not as module), partitions of type 0xfd are scanned and automatically assembled into RAID arrays. This autodetection may be suppressed with the kernel parameter "raid=noautodetect". As of kernel 2.6.9, only drives with a type 0 superblock can be autodetected and run at boot time.
mem=MEMEORY_SIZE
This is a classic parameter. Force usage of a specific amount of memory to be used when the kernel is not able to see the whole system memory or for test. For example:mem=1024M
The kernel command line is a null-terminated string currently up to 255 characters long, plus the final null. A string that is too long will be automatically truncated by the kernel, a boot loader may allow a longer command line to be passed to permit future kernels to extend this limit (H. Peter Anvin ).
Other parameters
initrd /boot/initrd.img
An initrd should be loaded. the boot process will load the kernel and an initial ramdisk; then the kernel converts initrd into a "normal" ramdisk, which is mounted read-write as root device; then /linuxrc is executed; afterwards the "real" root file system is mounted, and the initrd file system is moved over to /initrd; finally the usual boot sequence (e.g. invocation of /sbin/init) is performed. initrd is used to provide/load additional modules (device driver). For example, SCSI or RAID device driver loaded using initrd.
hdX =noprobe
Do not probe for hdX drive. For example, disable hdb hard disk:hdb=noprobe
If you disable hdb in BIOS, Linux will still detect it. This is the only way to disable hdb.
ether=irq,iobase,[ARG1,ARG2],name
Where,
- ether: ETHERNET DEVICES
For example, following boot argument force probing for a second Ethernet card (NIC), as the default is to only probe for one (irq=0,iobase=0 means automatically detect them).
ether=0,0,eth1
How to begin the enter parameters mode?
You need to enter all this parameter at Grub or Lilo boot prompt. For example if you are using Grub as a boot loader, at Grub prompt press 'e' to edit command before booting.
1) Select second line
2) Again, press 'e' to edit selected command
3) Type any of above parameters.
See an example of "", for more information. Another option is to type above parameters in grub.conf or lilo.conf file itself.
The following is a consolidated list of the kernel parameters as implemented (mostly) by the __setup() macro 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.
Module parameters for loadable modules are specified only as the parameter name with optional '=' and value as appropriate, such as:
modprobe usbcore blinkenlights=1
Module parameters for modules that are built into the kernel image are specified on the kernel command line with the module name plus '.' plus parameter name, with '=' and value if appropriate, such as:
usbcore.blinkenlights=1
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:
ACPI ACPI support is enabled.
ALSA ALSA sound support is enabled.
APIC APIC 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
EIDE EIDE/ATAPI support is enabled.
FB The frame buffer device is enabled.
HW Appropriate hardware is enabled.
IA-32 IA-32 aka i386 architecture is enabled.
IA-64 IA-64 architecture is enabled.
IOSCHED More than one I/O scheduler is enabled.
IP_PNP IP DHCP, BOOTP, or RARP is enabled.
ISAPNP ISA PnP code is enabled.
ISDN Appropriate ISDN support is enabled.
JOY Appropriate joystick support 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
Documentation/m68k/kernel-options.txt.
MCA MCA bus support is enabled.
MDA MDA console support is enabled.
MOUSE Appropriate mouse support is enabled.
MTD MTD 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.
PARIDE The ParIDE subsystem is enabled.
PARISC The PA-RISC architecture is enabled.
PCI PCI bus 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 has their options described inside of
Documentation/scsi/.
SELINUX SELinux support is enabled.
SERIAL Serial support is enabled.
SMP The kernel is an SMP kernel.
SPARC Sparc architecture is enabled.
SWSUSP Software suspend is enabled.
TS Appropriate touchscreen support is enabled.
USB USB support is enabled.
USBHID USB Human Interface Device support is enabled.
V4L Video For Linux support 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.
X86-64 X86-64 architecture is enabled.
More X86-64 boot options can be found in
Documentation/x86_64/boot-options.txt .
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
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.
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
Format: { force | off | ht | strict | noirq }
force -- enable ACPI if default was off
off -- disable ACPI if default was on
noirq -- do not use ACPI for IRQ routing
ht -- run only enough ACPI to enable Hyper Threading
strict -- Be less tolerant of platforms that are not
strictly ACPI specification compliant.
See also Documentation/pm.txt, pci=noacpi
acpi_sleep= [HW,ACPI] Sleep options
Format: { s3_bios, s3_mode }
See Documentation/power/video.txt
acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
Format: { level | edge | high | low }
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_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
use by PCI
Format: ,...
acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
Format: ,...
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_dbg_layer= [HW,ACPI]
Format:
Each bit of the 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]
Format:
Each bit of the 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.
acpi_fake_ecdt [HW,ACPI] Workaround failure due to BIOS lacking ECDT
acpi_generic_hotkey [HW,ACPI]
Allow consolidated generic hotkey driver to
override platform specific driver.
See also Documentation/acpi-hotkey.txt.
enable_timer_pin_1 [i386,x86-64]
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.
disable_timer_pin_1 [i386,x86-64]
Disable PIN 1 of APIC timer
Can be useful to work around chipset bugs.
ad1816= [HW,OSS]
Format: ,,,
See also Documentation/sound/oss/AD1816.
ad1848= [HW,OSS]
Format: ,,,,
adlib= [HW,OSS]
Format:
advansys= [HW,SCSI]
See header of drivers/scsi/advansys.c.
advwdt= [HW,WDT] Advantech WDT
Format: ,
aedsp16= [HW,OSS] Audio Excel DSP 16
Format: ,,,,,
See also header of sound/oss/aedsp16.c.
aha152x= [HW,SCSI]
See Documentation/scsi/aha152x.txt.
aha1542= [HW,SCSI]
Format: [,,[,]]
aic7xxx= [HW,SCSI]
See Documentation/scsi/aic7xxx.txt.
aic79xx= [HW,SCSI]
See Documentation/scsi/aic79xx.txt.
amijoy.map= [HW,JOY] Amiga joystick support
Map of devices attached to JOY0DAT and JOY1DAT
Format: ,
See also Documentation/kernel/input/joystick.txt
analog.map= [HW,JOY] Analog joystick and gamepad support
Specifies type or capabilities of an analog joystick
connected to one of 16 gameports
Format: ,,..
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,i386] 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.
apm= [APM] Advanced Power Management
See header of arch/i386/kernel/apm.c.
applicom= [HW]
Format: ,
arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
Format: ,,
ataflop= [HW,M68k]
atarimouse= [HW,MOUSE] Atari Mouse
atascsi= [HW,SCSI] Atari SCSI
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: (2 = AT (default), 3 = PS/2)
atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
keyboards
atkbd.softraw= [HW] Choose between synthetic and real raw mode
Format: (0 = real, 1 = synthetic (default))
atkbd.softrepeat= [HW]
Use software keyboard repeat
autotest [IA64]
awe= [HW,OSS] AWE32/SB32/AWE64 wave table synth
Format: ,,
aztcd= [HW,CD] Aztech CD268 CDROM driver
Format: ,0x79 (?)
baycom_epp= [HW,AX25]
Format: ,
baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
Format: ,
See header of drivers/net/hamradio/baycom_par.c.
baycom_ser_fdx= [HW,AX25]
BayCom Serial Port AX.25 Modem (Full Duplex Mode)
Format: ,,[,]
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: ,,
See header of drivers/net/hamradio/baycom_ser_hdx.c.
blkmtd_device= [HW,MTD]
blkmtd_erasesz=
blkmtd_ro=
blkmtd_bs=
blkmtd_count=
bttv.card= [HW,V4L] bttv (bt848 bt878 based grabber cards)
bttv.radio= Most important insmod options are available as
kernel args too.
bttv.pll= See Documentation/video4linux/bttv/Insmod-options
bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
BusLogic= [HW,SCSI]
See drivers/scsi/BusLogic.c, comment before function
BusLogic_ParseDriverOptions().
c101= [NET] Moxa C101 synchronous serial card
cachesize= [BUGS=IA-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.
cdu31a= [HW,CD]
Format: ,[,PAS]
See header of drivers/cdrom/cdu31a.c.
chandev= [HW,NET] Generic channel device initialisation
checkreqprot [SELINUX] Set initial checkreqprot flag value.
Format: { "0" | "1" }
See security/selinux/Kconfig help text.
0 -- check protection applied by kernel (includes
any implied execute protection).
1 -- check protection requested by application.
Default value is set via a kernel config option.
Value can be changed at runtime via
/selinux/checkreqprot.
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.
Format: { pit | tsc | cyclone | pmtmr }
hpet= [IA-32,HPET] option to disable HPET and use PIT.
Format: disable
cm206= [HW,CD]
Format: { auto | [,][] }
com20020= [HW,NET] ARCnet - COM20020 chipset
Format:
[,[,[,[,[,]]]]]
com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
Format: [,]
com90xx= [HW,NET]
ARCnet - COM90xx chipset (memory-mapped buffers)
Format: [,[,]]
condev= [HW,S390] console device
conmode=
console= [KNL] Output console device and options.
tty Use the virtual console device .
ttyS[,options]
Use the specified serial port. The options are of
the form "bbbbpn", where "bbbb" is the baud rate,
"p" is parity ("n", "o", or "e"), and "n" is bits.
Default is "9600n8".
See also Documentation/serial-console.txt.
uart,io,[,options]
uart,mmio,[,options]
Start an early, polled-mode console on the 8250/16550
UART at the specified I/O port or MMIO address,
switching to the matching ttyS device later. The
options are the same as for ttyS, above.
cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
Format:
,,,[,]
cpia_pp= [HW,PPT]
Format: { parport | auto | none }
crashkernel=nn[KMG]@ss[KMG]
[KNL] Reserve a chunk of physical memory to
hold a kernel to switch to with kexec on panic.
cs4232= [HW,OSS]
Format: ,,,,,
cs89x0_dma= [HW,NET]
Format:
cs89x0_media= [HW,NET]
Format: { rj45 | aui | bnc }
cyclades= [HW,SERIAL] Cyclades multi-serial port adapter.
dasd= [HW,NET]
See header of drivers/s390/block/dasd_devmap.c.
db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
(one device per port)
Format: ,
See also Documentation/input/joystick-parport.txt
debug [KNL] Enable kernel debugging (events log level).
decnet= [HW,NET]
Format: [,]
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.
digi= [HW,SERIAL]
IO parameters enable/disable command.
digiepca= [HW,SERIAL]
See drivers/char/README.epca and
Documentation/digiepca.txt.
dmascc= [HW,AX25,SERIAL] AX.25 Z80SCC driver with DMA
support available.
Format: [,[,..]]
dmasound= [HW,OSS] Sound subsystem buffers
dscc4.setup= [NET]
dtc3181e= [HW,SCSI]
earlyprintk= [IA-32,X86-64]
earlyprintk=vga
earlyprintk=serial[,ttySn[,baudrate]]
Append ",keep" to not disable it when the real console
takes over.
Only vga or serial at a time, not both.
Currently only ttyS0 and ttyS1 are supported.
Interaction with the standard serial driver is not
very good.
The VGA output is eventually overwritten by the real
console.
eata= [HW,SCSI]
eda= [HW,PS2]
edb= [HW,PS2]
edd= [EDD]
Format: {"of[f]" | "sk[ipmbr]"}
See comment in arch/i386/boot/edd.S
eicon= [HW,ISDN]
Format: ,,
eisa_irq_edge= [PARISC,HW]
See header of drivers/parisc/eisa.c.
elanfreq= [IA-32]
See comment before function elanfreq_setup() in
arch/i386/kernel/cpu/cpufreq/elanfreq.c.
elevator= [IOSCHED]
Format: {"as" | "cfq" | "deadline" | "noop"}
See Documentation/block/as-iosched.txt and
Documentation/block/deadline-iosched.txt for details.
elfcorehdr= [IA-32]
Specifies physical address of start of kernel core
image elf header.
See Documentation/kdump.txt for details.
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.
es1370= [HW,OSS]
Format: [,]
See also header of sound/oss/es1370.c.
es1371= [HW,OSS]
Format: ,[,[]]
See also header of sound/oss/es1371.c.
ether= [HW,NET] Ethernet cards parameters
This option is obsoleted by the "netdev=" option, which
has equivalent usage. See its documentation for details.
eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog.
Format: [,]
fd_mcs= [HW,SCSI]
See header of drivers/scsi/fd_mcs.c.
fdomain= [HW,SCSI]
See header of drivers/scsi/fdomain.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)
Format: ,,,,,
See also Documentation/input/joystick-parport.txt
gamma= [HW,DRM]
gdth= [HW,SCSI]
See header of drivers/scsi/gdth.c.
gpt [EFI] Forces disk with valid GPT signature but
invalid Protective MBR to be treated as GPT.
gscd= [HW,CD]
Format:
gt96100eth= [NET] MIPS GT96100 Advanced Communication Controller
gus= [HW,OSS]
Format: ,,,
gvp11= [HW,SCSI]
hashdist= [KNL,NUMA] Large hashes allocated during boot
are distributed across NUMA nodes. Defaults on
for IA-64, 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: ,,
hd?= [HW] (E)IDE subsystem
hd?lun= See Documentation/ide.txt.
highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
size of . This works even on boxes that have no
highmem otherwise. This also works to reduce highmem
size on bigger boxes.
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
(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.nomux [HW] Don't check presence of an active multiplexing
controller
i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
controllers
i8042.panicblink=
[HW] Frequency with which keyboard LEDs should blink
when kernel panics (default is 0.5 sec)
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
hardware.
i8k.force [HW] Activate i8k driver even if SMM BIOS signature
does not match list of supported models.
i8k.power_status
[HW] Report power status in /proc/i8k
(disabled by default)
i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
capability is set.
ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter
See Documentation/mca.txt.
icn= [HW,ISDN]
Format: [,[,[,]]]
ide= [HW] (E)IDE subsystem
Format: ide=nodma or ide=doubler or ide=reverse
See Documentation/ide.txt.
ide?= [HW] (E)IDE subsystem
Format: ide?=noprobe or chipset specific parameters.
See Documentation/ide.txt.
idebus= [HW] (E)IDE subsystem - VLB/PCI bus speed
See Documentation/ide.txt.
idle= [HW]
Format: idle=poll or idle=halt
ihash_entries= [KNL]
Set number of hash buckets for inode cache.
in2000= [HW,SCSI]
See header of drivers/scsi/in2000.c.
init= [KNL]
Format:
Run specified binary instead of /sbin/init as init
process.
initcall_debug [KNL] Trace initcalls as they are executed. Useful
for working out where the kernel is dying during
startup.
initrd= [BOOT] Specify the location of the initial ramdisk
inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
Format:
inttest= [IA64]
io7= [HW] IO7 for Marvel based alpha systems
See comment before marvel_specify_io7 in
arch/alpha/kernel/core_marvel.c.
ip= [IP_PNP]
See Documentation/nfsroot.txt.
ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
See comment before ip2_setup() in drivers/char/ip2.c.
ips= [HW,SCSI] Adaptec / IBM ServeRAID controller
See header of drivers/scsi/ips.c.
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: ,,,
isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
Format: ,...,
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
an "isolated" CPU is via the CPU affinity syscalls.
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.
isp16= [HW,CD]
Format: ,,,
iucv= [HW,NET]
js= [HW,JOY] Analog joystick
See Documentation/input/joystick.txt.
keepinitrd [HW,ARM]
kstack=N [IA-32,X86-64] Print N words from the kernel stack
in oops dumps.
l2cr= [PPC]
lapic [IA-32,APIC] Enable the local APIC even if BIOS
disabled it.
lasi= [HW,SCSI] PARISC LASI driver for the 53c700 chip
Format: addr:,irq:
llsc*= [IA64] See function print_params() in
arch/ia64/sn/kernel/llsc4.c.
load_ramdisk= [RAM] List of ramdisks to load from floppy
See Documentation/ramdisk.txt.
lockd.udpport= [NFS]
lockd.tcpport= [NFS]
logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
Format:
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 Sets the size of the printk ring buffer, in bytes.
Format: { n | nk | nM }
n must be a power of two. The default size
is set in the kernel config file.
lp=0 [LP] Specify parallel ports to use, e.g,
lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
lp=reset first parallel port). 'lp=0' disables the
lp=auto printer driver. 'lp=reset' (which can be
specified in addition to the ports) causes
attached printers to be reset. Using
lp=port1,port2,... specifies the parallel ports
to associate lp devices with, starting with
lp0. A port specification may be 'none' to skip
that lp device, or a parport name such as
'parport0'. Specifying 'lp=auto' instead of a
port specification list means that device IDs
from each port should be examined, to see if
an IEEE 1284-compliant printer is attached; if
so, the driver will manage that printer.
See also header of drivers/char/lp.c.
lpj=n [KNL]
Sets loops_per_jiffy to given constant, thus avoiding
time-consuming boot-time autodetection (up to 250 ms per
CPU). 0 enables autodetection (default). To determine
the correct value for your kernel, boot with normal
autodetection and see what value is printed. Note that
on SMP systems the preset will be applied to all CPUs,
which is likely to cause problems if your CPUs need
significantly divergent settings. An incorrect value
will cause delays in the kernel to be wrong, leading to
unpredictable I/O errors and other breakage. Although
unlikely, in the extreme case this might damage your
hardware.
ltpc= [NET]
Format: ,,
mac5380= [HW,SCSI] Format:
,,,,
mac53c9x= [HW,SCSI] Format:
,,,,,,,
machvec= [IA64] Force the use of a particular machine-vector
(machvec) in a generic kernel.
Example: machvec=hpzx1_swiotlb
mad16= [HW,OSS] Format:
,,,,,,
maui= [HW,OSS]
Format: ,
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
max_addr=[KMG] [KNL,BOOT,ia64] All physical memory greater than or
equal to this physical address is ignored.
max_luns= [SCSI] Maximum number of LUNs to probe.
Should be between 1 and 2^32-1.
max_report_luns=
[SCSI] Maximum number of LUNs received.
Should be between 1 and 16384.
mca-pentium [BUGS=IA-32]
mcatest= [IA-64]
mcd= [HW,CD]
Format: ,,
mcdx= [HW,CD]
mce [IA-32] Machine Check Exception
md= [HW] RAID subsystems devices and level
See Documentation/md.txt.
mdacon= [MDA]
Format: ,
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.
[IA-32] 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=IA-32] Disable usage of 4MB pages for kernel
memory.
memmap=exactmap [KNL,IA-32] Enable setting of an exact
E820 memory map, as specified by the user.
Such memmap=exactmap lines can be constructed based on
BIOS output or other requirements. See the memmap=nn@ss
option description.
memmap=nn[KMG]@ss[KMG]
[KNL] Force usage of a specific region of memory
Region of memory to be used, from ss to ss nn.
memmap=nn[KMG]#ss[KMG]
[KNL,ACPI] Mark specific memory as ACPI data.
Region of memory to be used, from ss to ss nn.
memmap=nn[KMG]$ss[KMG]
[KNL,ACPI] Mark specific memory as reserved.
Region of memory to be used, from ss to ss nn.
meye.*= [HW] Set MotionEye Camera parameters
See Documentation/video4linux/meye.txt.
mga= [HW,DRM]
mousedev.tap_time=
[MOUSE] Maximum time between finger touching and
leaving touchpad surface for touch to be considered
a tap and be reported as a left button click (for
touchpads working in absolute mode only).
Format:
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
mpu401= [HW,OSS]
Format: ,
MTD_Partition= [MTD]
Format: ,,,
MTD_Region= [MTD] Format:
,[,,,]
mtdparts= [MTD]
See drivers/mtd/cmdline.c.
mtouchusb.raw_coordinates=
[HW] Make the MicroTouch USB driver use raw coordinates
('y', default) or cooked coordinates ('n')
n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
NCR_D700= [HW,SCSI]
See header of drivers/scsi/NCR_D700.c.
ncr5380= [HW,SCSI]
ncr53c400= [HW,SCSI]
ncr53c400a= [HW,SCSI]
ncr53c406a= [HW,SCSI]
ncr53c8xx= [HW,SCSI]
netdev= [NET] Network devices parameters
Format: ,,,,
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.
nfsaddrs= [NFS]
See Documentation/nfsroot.txt.
nfsroot= [NFS] nfs root filesystem for disk-less boxes.
See Documentation/nfsroot.txt.
nmi_watchdog= [KNL,BUGS=IA-32] Debugging features for SMP kernels
no387 [BUGS=IA-32] Tells the kernel to use the 387 maths
emulation library even if a 387 maths coprocessor
is present.
noalign [KNL,ARM]
noapic [SMP,APIC] Tells the kernel to not make use of any
IOAPICs that may be present in the system.
noasync [HW,M68K] Disables async and sync negotiation for
all devices.
nobats [PPC] Do not use BATs for mapping kernel lowmem
on "Classic" PPC cores.
nocache [ARM]
nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
noexec [IA-64]
noexec [IA-32,X86-64]
noexec=on: enable non-executable mappings (default)
noexec=off: disable nn-executable mappings
nofxsr [BUGS=IA-32]
nohlt [BUGS=ARM]
no-hlt [BUGS=IA-32] Tells the kernel that the hlt
instruction doesn't work correctly and not to
use it.
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.
noirqdebug [IA-32] Disables the code which attempts to detect and
disable unhandled interrupt sources.
noisapnp [ISAPNP] Disables ISA PnP code.
noinitrd [RAM] Tells the kernel not to load any configured
initial RAM disk.
nointroute [IA-64]
nolapic [IA-32,APIC] Do not enable or use the local APIC.
noltlbs [PPC] Do not use large page/tlb entries for kernel
lowmem mapping on PPC40x.
nomce [IA-32] Machine Check Exception
noresidual [PPC] Don't use residual data on PReP machines.
noresume [SWSUSP] Disables resume and restores original swap
space.
no-scroll [VGA] Disables scrollback.
This is required for the Braillex ib80-piezo Braille
reader made by F.H. Papenmeier (Germany).
nosbagart [IA-64]
nosmp [SMP] Tells an SMP kernel to act as a UP kernel.
nosync [HW,M68K] Disables sync negotiation for all devices.
notsc [BUGS=IA-32] Disable Time Stamp Counter
nousb [USB] Disable the USB subsystem
nowb [ARM]
opl3= [HW,OSS]
Format:
opl3sa= [HW,OSS]
Format: ,,,,,
opl3sa2= [HW,OSS] Format:
,,,,,,,[,,
osst= [HW,SCSI] SCSI Tape Driver
Format: ,
See also Documentation/scsi/st.txt.
panic= [KNL] Kernel behaviour on panic
Format:
parkbd.port= [HW] Parallel port number the keyboard adapter is
connected to, default is 0.
Format:
parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
0 for XT, 1 for AT (default is AT).
Format:
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]
pas2= [HW,OSS] Format:
,,,,,,,
pas16= [HW,SCSI]
See header of drivers/scsi/pas16.c.
pcbit= [HW,ISDN]
pcd. [PARIDE]
See header of drivers/block/paride/pcd.c.
See also Documentation/paride.txt.
pci=option[,option...] [PCI] various PCI subsystem options:
off [IA-32] don't probe for the PCI bus
bios [IA-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 [IA-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 [IA-32] Force use of PCI Configuration
Mechanism 1.
conf2 [IA-32] Force use of PCI Configuration
Mechanism 2.
nosort [IA-32] Don't sort PCI devices according to
order given by the PCI BIOS. This sorting is
done to get a device order compatible with
older kernels.
biosirq [IA-32] Use PCI BIOS calls to get the interrupt
routing table. These calls are known to be buggy
on several machines and they hang the machine
when used, but on other computers it's the only
way to get the interrupt routing table. Try
this option if the kernel is unable to allocate
IRQs or discover secondary PCI buses on your
motherboard.
rom [IA-32] Assign address space to expansion ROMs.
Use with caution as certain devices share
address decoders between ROMs and other
resources.
irqmask=0xMMMM [IA-32] 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 [IA-32] Specify the physical address
of the PIRQ table (normally generated
by the BIOS) if it is outside the
F0000h-100000h range.
lastbus=N [IA-32] 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 [IA-32] Always assign all PCI bus
numbers ourselves, overriding
whatever the firmware may have done.
usepirqmask [IA-32] 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 [IA-32] Do not use ACPI for IRQ routing
or for PCI scanning.
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.
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.
pcmv= [HW,PCMCIA] BadgePAD 4
pd. [PARIDE]
See Documentation/paride.txt.
pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
boot time.
Format: { 0 | 1 }
See arch/parisc/kernel/pdc_chassis.c
pf. [PARIDE]
See Documentation/paride.txt.
pg. [PARIDE]
See Documentation/paride.txt.
pirq= [SMP,APIC] Manual mp-table setup
See Documentation/i386/IO-APIC.txt.
plip= [PPT,NET] Parallel port network link
Format: { parport | timid | 0 }
See also Documentation/parport.txt.
pnpacpi= [ACPI]
{ off }
pnpbios= [ISAPNP]
{ on | off | curr | res | no-curr | no-res }
pnp_reserve_irq=
[ISAPNP] Exclude IRQs for the autoconfiguration
pnp_reserve_dma=
[ISAPNP] Exclude DMAs for the autoconfiguration
pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
Ranges are in pairs (I/O port base and size).
pnp_reserve_mem=
[ISAPNP] Exclude memory regions for the
autoconfiguration.
Ranges are in pairs (memory base and size).
profile= [KNL] Enable kernel profiling via /proc/profile
Format: [schedule,]
Param: "schedule" - profile schedule points.
Param: - step/bucket size as a power of 2 for
statistical time based profiling.
processor.max_cstate= [HW,ACPI]
Limit processor to maximum C-state
max_cstate=9 overrides any DMI blacklist limit.
prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
before loading.
See Documentation/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).
psmouse.resolution=
[HW,MOUSE] Set desired mouse resolution, in dpi.
psmouse.smartscroll=
[HW,MOUSE] Controls Logitech smartscroll autorepeat.
0 = disabled, 1 = enabled (default).
pss= [HW,OSS] Personal Sound System (ECHO ESC614)
Format:
,,,,,
pt. [PARIDE]
See Documentation/paride.txt.
quiet= [KNL] Disable log messages
r128= [HW,DRM]
raid= [HW,RAID]
See Documentation/md.txt.
ramdisk= [RAM] Sizes of RAM disks in kilobytes [deprecated]
See Documentation/ramdisk.txt.
ramdisk_blocksize= [RAM]
See Documentation/ramdisk.txt.
ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
New name for the ramdisk parameter.
See Documentation/ramdisk.txt.
rdinit= [KNL]
Format:
Run specified binary instead of /init from the ramdisk,
used for early userspace startup. See initrd.
reboot= [BUGS=IA-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
Format: [,[,...]]
See arch/*/kernel/reboot.c.
reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
resume= [SWSUSP]
Specify the partition device for software suspend
rhash_entries= [KNL,NET]
Set number of hash buckets for route cache
riscom8= [HW,SERIAL]
Format: [,[,...]]
ro [KNL] Mount root device read-only on boot
root= [KNL] Root filesystem
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
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.
sb= [HW,OSS]
Format: ,,,
sbni= [NET] Granch SBNI12 leased line adapter
sbpcd= [HW,CD] Soundblaster CD adapter
Format: ,
See a comment before function sbpcd_setup() in
drivers/cdrom/sbpcd.c.
sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver
Format: