Difference between revisions of "Kernel parameters"

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[[Category:Kernel]]
 
[[Category:Kernel]]
[[en:Kernel parameters]]
 
 
[[es:Kernel parameters]]
 
[[es:Kernel parameters]]
 
[[ja:Kernel parameters]]
 
[[ja:Kernel parameters]]
 
[[zh-CN:Kernel parameters]]
 
[[zh-CN:Kernel parameters]]
 
 
There are three ways to pass options to the kernel and thus control its behaviour:
 
There are three ways to pass options to the kernel and thus control its behaviour:
  
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* Press {{Keypress|Tab}} when the menu shows up and add them at the end of the string:
 
* Press {{Keypress|Tab}} when the menu shows up and add them at the end of the string:
  
: {{bc|1=> .linux ../vmlinuz-linux root=/dev/sda3 ro initrd=../initramfs-linux.img ''quiet splash''}}
+
: {{bc|1=linux /boot/vmlinuz-linux root=/dev/sda3 initrd=/boot/initramfs-linux.img ''quiet splash''}}
  
 
: Press {{Keypress|Enter}} to boot with these parameters.
 
: Press {{Keypress|Enter}} to boot with these parameters.
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* To make the change persistent after reboot, edit {{ic|/boot/syslinux/syslinux.cfg}} and add them to the {{ic|APPEND}} line:
 
* To make the change persistent after reboot, edit {{ic|/boot/syslinux/syslinux.cfg}} and add them to the {{ic|APPEND}} line:
  
: {{bc|1=APPEND root=/dev/sda3 ro ''quiet splash''}}
+
: {{bc|1=APPEND root=/dev/sda3 ''quiet splash''}}
  
 
For more information on configuring Syslinux, see the [[Syslinux]] article.
 
For more information on configuring Syslinux, see the [[Syslinux]] article.
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* Press {{Keypress|e}} when the menu shows up and add them on the {{ic|linux}} line:
 
* Press {{Keypress|e}} when the menu shows up and add them on the {{ic|linux}} line:
  
: {{bc|1=linux   /boot/vmlinuz-linux root=UUID=978e3e81-8048-4ae1-8a06-aa727458e8ff ro  ''quiet splash''}}
+
: {{bc|1=linux /boot/vmlinuz-linux root=UUID=978e3e81-8048-4ae1-8a06-aa727458e8ff ''quiet splash''}}
  
 
: Press {{Keypress|b}} to boot with these parameters.
 
: Press {{Keypress|b}} to boot with these parameters.
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* Press {{Keypress|e}} when the menu shows up and add them on the {{ic|kernel}} line:
 
* Press {{Keypress|e}} when the menu shows up and add them on the {{ic|kernel}} line:
  
: {{bc|1=kernel /boot/vmlinuz-linux root=/dev/sda3 ro ''quiet splash''}}
+
: {{bc|1=kernel /boot/vmlinuz-linux root=/dev/sda3 ''quiet splash''}}
  
 
: Press {{Keypress|b}} to boot with these parameters.
 
: Press {{Keypress|b}} to boot with these parameters.
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For more information on configuring LILO, see the [[LILO]] article.
 
For more information on configuring LILO, see the [[LILO]] article.
  
== Parameters list ==
+
== Parameter list ==
  
{{Expansion|The list needs more parameters.}}
+
Parameters always come in {{ic|parameter}} or {{ic|1=parameter=value}}. All of these parameters are case-sensitive.
  
 
{{Note|Not all of the listed options are always available. Most are associated with subsystems and work only if the kernel is configured with those subsystems built in. They also depend on the presence of the hardware they are associated with.}}
 
{{Note|Not all of the listed options are always available. Most are associated with subsystems and work only if the kernel is configured with those subsystems built in. They also depend on the presence of the hardware they are associated with.}}
  
 
{| border="1"
 
{| border="1"
![[SysVinit]]!![[systemd]]!!Description
+
!parameter!!Description
 
|-
 
|-
| {{ic|3}} || {{ic|1=systemd.unit=multi-user}} || Boot to a specified runlevel (3, in this case). Works with 1-6.
+
|{{ic|1=root=}}|| Root filesystem.
 
|-
 
|-
| {{ic|1}}  || {{ic|1=systemd.unit=rescue}} || Boot to Single-user mode (root).
+
|{{ic|1=ro}}|| Mount root device read-only on boot.
 
|-
 
|-
| {{ic|nomodeset}} || {{ic|nomodeset}} || Disable [[Kernel Mode Setting]].
+
|{{ic|1=rw}}|| Mount root device read-write on boot (default).
 
|-
 
|-
| {{ic|1=loglevel=3}} || {{ic|1=loglevel=3}} || Removes "misaligned reg" and "unknown connector type" messages during boot with the [[Nouveau]] driver. See [https://bbs.archlinux.org/viewtopic.php?id=137509 this] topic.
+
|{{ic|1=initrd=}}|| Specify the location of the initial ramdisk.
 
|-
 
|-
| -- || {{ic|1=init=/usr/lib/systemd/systemd}} || Boot using [[Systemd#Installation|systemd]] instead of SysVinit.
+
|{{ic|1=init=}}|| Run specified binary instead of {{ic|/sbin/init}} (symlinked to [[systemd]] in Arch) as init process.
 +
|-
 +
|{{ic|1=init=/bin/sh}}|| Boot to shell.
 +
|-
 +
|{{ic|1=systemd.unit=}}||
 +
|-
 +
|{{ic|1=systemd.unit=multi-user}}|| Boot to a specified runlevel.
 +
|-
 +
|{{ic|1=systemd.unit=rescue}}|| Boot to single-user mode (root).
 +
|-
 +
|{{ic|nomodeset}}|| Disable [[Kernel Mode Setting]].
 
|-
 
|-
| {{ic|1=init=/bin/sh rw}}  || {{ic|1=init=/bin/sh rw}} || Boot to Shell.
 
 
 
|}
 
|}
  
All of these parameters are case-sensitive.
+
For a complete list of all options, please see the [https://www.kernel.org/doc/Documentation/kernel-parameters.txt kernel documentation].
 
+
For a complete list of all known options, please see the [https://www.kernel.org/doc/Documentation/kernel-parameters.txt kernel documentation].
+
  
== See Also ==
+
== See also ==
  
 
* [[sysctl]]
 
* [[sysctl]]
 +
* [[Power saving#Kernel parameters]]
 
* [http://files.kroah.com/lkn/lkn_pdf/ch09.pdf List of kernel parameters with further explanation and grouped by similar options]
 
* [http://files.kroah.com/lkn/lkn_pdf/ch09.pdf List of kernel parameters with further explanation and grouped by similar options]

Revision as of 20:03, 7 August 2013

There are three ways to pass options to the kernel and thus control its behaviour:

  1. When building the kernel.
  2. When starting the kernel (usually, when invoked from a boot loader).
  3. At runtime (through the files in /proc and /sys).

This page now explains in more detail the second method and shows a list of most used kernel parameters in Arch Linux.

Configuration

Kernel parameters can be set either temporarily by editing the boot menu when it shows up, or by modifying the boot loader's configuration file.

Here we are adding the parameters quiet and splash to Syslinux, GRUB, GRUB Legacy and LILO.

Syslinux

  • Press Template:Keypress when the menu shows up and add them at the end of the string:
linux /boot/vmlinuz-linux root=/dev/sda3 initrd=/boot/initramfs-linux.img quiet splash
Press Template:Keypress to boot with these parameters.
  • To make the change persistent after reboot, edit /boot/syslinux/syslinux.cfg and add them to the APPEND line:
APPEND root=/dev/sda3 quiet splash

For more information on configuring Syslinux, see the Syslinux article.

GRUB

linux /boot/vmlinuz-linux root=UUID=978e3e81-8048-4ae1-8a06-aa727458e8ff quiet splash
Press Template:Keypress to boot with these parameters.
  • To make the change persistent after reboot, while you could manually edit /boot/grub/grub.cfg with the exact line from above, for beginners it's recommended to:
Edit /etc/default/grub and append your kernel options to the GRUB_CMDLINE_LINUX_DEFAULT line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
And then automatically re-generate the grub.cfg file with:
# grub-mkconfig -o /boot/grub/grub.cfg

For more information on configuring GRUB, see the GRUB article.

GRUB Legacy

kernel /boot/vmlinuz-linux root=/dev/sda3 quiet splash
Press Template:Keypress to boot with these parameters.
  • To make the change persistent after reboot, edit /boot/grub/menu.lst and add them to the kernel line, exactly like above.

For more information on configuring GRUB Legacy, see the GRUB Legacy article.

LILO

  • Add them to /etc/lilo.conf:
image=/boot/vmlinuz-linux
        ...
        quiet splash

For more information on configuring LILO, see the LILO article.

Parameter list

Parameters always come in parameter or parameter=value. All of these parameters are case-sensitive.

Note: Not all of the listed options are always available. Most are associated with subsystems and work only if the kernel is configured with those subsystems built in. They also depend on the presence of the hardware they are associated with.
parameter Description
root= Root filesystem.
ro Mount root device read-only on boot.
rw Mount root device read-write on boot (default).
initrd= Specify the location of the initial ramdisk.
init= Run specified binary instead of /sbin/init (symlinked to systemd in Arch) as init process.
init=/bin/sh Boot to shell.
systemd.unit=
systemd.unit=multi-user Boot to a specified runlevel.
systemd.unit=rescue Boot to single-user mode (root).
nomodeset Disable Kernel Mode Setting.

For a complete list of all options, please see the kernel documentation.

See also