Guides for setting kernel parameters

Overview#

These vary with architecture and specific device

Linux kernel guide to its parameters#

https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html

A suggested tweak#

Adding consoleblank=300 can be a nice addition to the kernel commandline. It blanks a text console if left idle for over 300 seconds (5 minutes). In same cases that will allow a monitor to do some power saving (although it is not display ‘sleep’ mode).

Modifying files on the boot partition#

If your boot partition is mounted on /media/mmcblk0p1, you need to make /media/mmcblk0p1 read-write before you can make changes. To do so execute:

mount -o remount,rw /media/mmcblk0p1

change what you need, then return to read-only status

mount -o remount,ro /media/mmcblk0p1

Hint: Typical x86-64 systems will likely use /media/sda1 rather than /media/mmcblk0. You will need to verify the name of the storage device and adjust these instructions accordingly.

NOTE: It is recommended that you do not make this partition read-write under normal conditions. This avoids accidental writes which could render your system unbootable.

Systems using Syslinux for bootloader#

WARNING: Changing the kernel commandline or boot configuration can render your system unbootable, depending on the parameters you change.

Edit syslinux.cfg in the boot partition. For example, /media/sda1/boot/syslinux/syslinux.cfg.

The default x86-64 commandline in syslinux.cfg:

APPEND modules=loop,squashfs,sd-mod,usb-storage quiet

Systems using GRUB for bootloader#

WARNING: Changing the kernel commandline or boot configuration can render your system unbootable, depending on the parameters you change.

Edit grub.cfg in the boot partition. For example, /media/sda1/boot/grub/grub.cfg

The default x86-64 commandline in grub.cfg:

linux    /boot/vmlinuz-lts modules=loop,squashfs,sd-mod,usb-storage quiet

Systems using U-boot#

TODO: Booting using u-boot from https://denx.com

Raspberry Pi#

Kernel parameter setting (boot time)#

WARNING: Changing the kernel commandline can render your system unbootable, depending on the parameters you change.

/media/mmcblk0p1/commandline.txt is passed verbatim to the kernel at the end of the kernel commandline. Edit to suit your needs.

Device-tree (config.txt/usercfg.txt)#

See GrayJack’s very complete and documented config.txt file for raspberry pi on GitHub (Gist) for information.

/media/mmcblk0p1/usercfg.txt: The preferred location for setting certain hardware configuration options.

/media/mmcblk0p1/config.txt : Is replaced on kernel updates so it is recommended that you do not use this location for your settings. Instead use usercfg.txt. Unfortunately, some parameters like gpu_mem=32 will not be honoured in usercfg.txt and therefore you must edit config.txt and remember to update on kernel update. (see Raspberry Pi firmware GitHub issue #1332)