Kernel parameters
There are three ways to pass options to the kernel and thus control its behaviour:
- When building the kernel. See Kernel Compilation for details.
- When starting the kernel (usually, when invoked from a boot loader).
- At runtime (through the files in
/procand/sys). See sysctl for details.
This page now explains in more detail the second method and shows a list of most used kernel parameters in Arch Linux.
Contents
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.
The following examples add the quiet and splash parameters to Syslinux, systemd-boot, GRUB, GRUB Legacy, LILO, and rEFInd.
Syslinux
- Press
Tabwhen 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
Enterto boot with these parameters.
- To make the change persistent after reboot, edit
/boot/syslinux/syslinux.cfgand add them to theAPPENDline:
-
APPEND root=/dev/sda3 quiet splash
For more information on configuring Syslinux, see the Syslinux article.
systemd-boot
- Press
ewhen the menu appears and add the parameters to the end of the string:
-
initrd=\initramfs-linux.img root=/dev/sda2 quiet splash
- Press
Enterto boot with these parameters.
- To make the change persistent after reboot, edit
/boot/loader/entries/arch.conf(assuming you set up your EFI System Partition) and add them to theoptionsline:
-
options root=/dev/sda2 quiet splash
For more information on configuring systemd-boot, see the systemd-boot article.
GRUB
- Press
ewhen the menu shows up and add them on thelinuxline:
-
linux /boot/vmlinuz-linux root=UUID=978e3e81-8048-4ae1-8a06-aa727458e8ff quiet splash
- Press
Ctrl+xto boot with these parameters.
- To make the change persistent after reboot, while you could manually edit
/boot/grub/grub.cfgwith the exact line from above, the best practice is to:
- Edit
/etc/default/gruband append your kernel options to theGRUB_CMDLINE_LINUX_DEFAULTline:
-
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
-
- And then automatically re-generate the
grub.cfgfile with:
-
# grub-mkconfig -o /boot/grub/grub.cfg
-
For more information on configuring GRUB, see the GRUB article.
GRUB Legacy
- Press
ewhen the menu shows up and add them on thekernelline:
-
kernel /boot/vmlinuz-linux root=/dev/sda3 quiet splash
- Press
bto boot with these parameters.
- To make the change persistent after reboot, edit
/boot/grub/menu.lstand add them to thekernelline, 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.
rEFInd
- To make the change persistent after reboot, edit
/boot/refind_linux.confand append them to all/required lines, for example
-
"Boot using default options" "root=PARTUUID=978e3e81-8048-4ae1-8a06-aa727458e8ff rw quiet splash"
- If you have disabled auto-detection of OSes in rEFInd and are defining OS stanzas instead in
esp/refind/refind.confto load your OSes, you can edit it like:
-
menuentry "Arch Linux" { ... options "root=PARTUUID=978e3e81-8048-4ae1-8a06-aa727458e8ff rw quiet splash" ... }
For more information on configuring kernel parameters in rEFInd, see Configuring the rEFInd Bootmanager
EFISTUB
See EFISTUB#Using UEFI directly.
Hijacking cmdline
Even without access to your bootloader it is possible to change your kernel parameters to enable debugging (if you have root access). This can be accomplished by overwriting /proc/cmdline which stores the kernel parameters. However /proc/cmdline is not writable even as root, so this hack is accomplished by using a bind mount to mask the path.
First create a file containing the desired kernel parameters
/root/cmdline
root=/dev/disk/by-label/ROOT ro console=tty1 logo.nologo debug
Then use a bind mount to overwrite the parameters
# mount -n --bind -o ro /root/cmdline /proc/cmdline
The -n option skips adding the mount to /etc/mtab, so it will work even if root is mounted read-only. You can cat /proc/cmdline to confirm that your change was successful.
Parameter list
Parameters always come in parameter or parameter=value. All of these parameters are case-sensitive.
| parameter | Description |
|---|---|
| root= | Root filesystem. |
| rootflags= | Root filesystem mount options. |
| ro | Mount root device read-only on boot (default1). |
| rw | Mount root device read-write on boot. |
| 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= | Boot to a specified target. |
| nomodeset | Disable Kernel mode setting. |
| zswap.enabled | Enable Zswap. |
| video=<videosetting> | Override framebuffer video defaults. |
1 mkinitcpio uses ro as default value when neither rw or ro is set by the boot loader. Boot loaders may set the value to use, for example GRUB uses rw by default (see FS#36275 as a reference).
For a complete list of all options, please see the kernel documentation.