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 explains in more detail the second method and shows a list of the most used kernel parameters in Arch Linux.
Not all parameters 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.
Parameters either have the format parameter or parameter=value.
Contents
Configuration
- You can check the parameters your system was booted up with by running
cat /proc/cmdlineand see if it includes your changes. - The Arch Linux installation medium uses Syslinux for BIOS systems, and systemd-boot for UEFI systems.
Kernel parameters can be set either temporarily by editing the boot entry in the boot loader's boot selection menu, 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.
- If you have not set a value for menu timeout, you will need to hold
Spacewhile booting for the systemd-boot menu to appear. - If you cannot edit the parameters from the boot menu, you may need to edit
/boot/loader/loader.confand addeditor 1to enable editing.
- 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, you could manually edit
/boot/grub/grub.cfgwith the exact line from above, but 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
- Press
+,F2, orInserton the desired menu entry and press it again on the submenu entry. Add kernel parameters at the end of the string:
root=PARTUUID=978e3e81-8048-4ae1-8a06-aa727458e8ff rw initrd=\boot\initramfs-linux.img quiet splash
- Press
Enterto boot with these parameters.
- 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/EFI/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 rEFInd, see the rEFInd article.
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
This list is not comprehensive. For a complete list of all options, please see the kernel documentation.
| parameter | Description |
|---|---|
| root= | Root filesystem. See init/do_mounts.c for supported device name formats. |
| 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 as init process. The systemd-sysvcompat package symlinks /sbin/init to /usr/lib/systemd/systemd to use systemd.
|
| init=/bin/sh | Boot to shell. |
| systemd.unit= | Boot to a specified target. |
| resume= | Specify a swap device to use when waking from hibernation. |
| nomodeset | Disable Kernel mode setting. |
| zswap.enabled | Enable Zswap. |
| panic= | Time before automatic reboot on kernel panic. |
| debug | Enable kernel debugging (events log level). |
| mem= | Force usage of a specific amount of memory to be used. |
| maxcpus= | Maximum number of processors that an SMP kernel will bring up during bootup. |
| selinux= | Disable or enable SELinux at boot time. |
| netdev= | Network devices parameters. |
| video= | 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).