bootloader_config.md

Bootloader configuration

Once the initramfs image has been created, the system must be configured to use it. Depending on the booloader, this can be done in different ways.

efibootmgr configuration

If the kernel is built with the CONFIG_EFI_STUB option, the path of the initramfs can be passed to it with the initrd= command line option.

This can be set with:

efibootmgr -c -d /dev/sda -L "Gentoo UGRD" -l 'vmlinuz-gentoo.efi' -u 'initrd=ugrd.cpio'

This example assumes that the ESP is the first partition on /dev/sda, the kernel is named vmlinuz-gentoo.efi under the root of the ESP, and ugrd.cpio is also on the ESP root.

On some systems, the EFI may remove entries that don't follow a particular format.

Embedding the initramfs image into the kernel

The initramfs image can be embedded into the kernel image itself. This can be done by setting the CONFIG_INITRAMFS_SOURCE option in the kernel configuration.

The build_dircan be embedded into the Linux kernel with:

CONFIG_INITRAMFS_SOURCE="/tmp/initramfs"

A CPIO file can be embedded into the Linux kernel with:

CONFIG_INITRAMFS_SOURCE="/usr/src/initramfs/ugrd.cpio"

The CPIO must be decompressed before being embedded.

Making the kernel automatically search for the initamfs image

To make the kernel try to load a specific initrd file at boot, without embedding it:

CONFIG_CMDLINE_BOOL=y
CONFIG_CMDLINE="initrd=ugrd.cpio"

This will use ugrd.cpio under the ESP.