Efibootmgr

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efibootmgr is a tool for managing UEFI boot entries.

It is not a bootloader. It is a tool that interacts with the EFI firmware of the system, which itself is acting as a bootloader. Using efibootmgr boot entries can be created, reshuffled and removed.

Installation

Kernel

CONFIG_EFI_VARS support needs to be enabled:

KERNEL Enable EFI variable support

Firmware Drivers  --->
   EFI (Extensible Firmware Interface) Support  --->
       <*> EFI Variable Support via sysfs

Emerge

The sys-boot/efibootmgr package does not have any USE flags. All that is needed is to install it:

root #emerge --ask sys-boot/efibootmgr

Configuration

EFI vars

In order to successfully use efibootmgr the EFI variables filesystem must be accessible. This requires that the system has been booted in EFI mode (and not through the firmware's MBR mode) as otherwise the EFI variables themselves cannot be accessed. If the system is in MBR mode, reboot and do what is necessary in order to tell the system firmware to boot in EFI mode. Usually this involved either changing an option in the firmware's settings or selecting an EFI boot entry in the system's boot menu.

When the system is in EFI mode, run the following command to check for the existence of efivarfs:

root #mount | grep efivars

efivarfs on /sys/firmware/efi/efivars type efivarfs (ro,relatime)

It is mounted ro through the sysfs init script), so it needs to be remounted rw manually using the following command:

root #mount -o remount,rw -t efivarfs efivarfs /sys/firmware/efi/efivars

Preconditions

If an EFI System Partition (ESP) does not exist, one needs to be created, see EFI System Partition

Usage

Listing boot entries

To list the current boot entries by using the --verbose (-v) option:

root #efibootmgr -v

BootCurrent: 0002
Timeout: 3 seconds
BootOrder: 0003,0003,0002,0000,0004
Boot0000* CD/DVD Drive  BIOS(3,0,00)
Boot0001* Hard Drive    BIOS(2,0,00)
Boot0002* Gentoo        HD(1,800,61800,6d98f360-cb3e-4727-8fed-5ce0c040365d)File(\EFI\boot\bootx64.efi)
Boot0003* Hard Drive    BIOS(2,0,00)P0: ST1500DM003-9YN16G

Creating a boot entry

To create an EFI boot entry, a couple of arguments are passed to efibootmgr:

--create (-c) to create a new entry;
--part (-p) followed by the partition number on which the EFI System Partition is hosted;
--disk (-d) followed by the disk on which the EFI System Partition is hosted;
--label (-L) followed by the label to use as the boot entry;
--loader (-l) followed by the path of the EFI image to boot

Important
The path of the EFI image to boot must use \ (backslash) instead of / (forward slash) as path separator.

For instance:

root #efibootmgr -c -d /dev/sda -p 2 -L "Gentoo" -l "\efi\boot\bootx64.efi"

Optionally, additional kernels can be installed and made known to the UEFI firmware. This is especially useful when wanting to test more kernels or to dual-boot with another operating system. These will be shown in the boot selection prompt, normally after a keyboard hotkey is pressed at the right time during system initialization. The latest added entry always gets highest boot priority, so it will be default. If the hotkey combination is unknown, search for official documentation from the computer manufacturer. This information is usually not difficult to find.

Deleting a boot entry

Before deleting an entry, first figure out what ID the entry has.

To delete the Gentoo entry as shown above (which has Boot0002 as the identifier), ask efibootmgr to delete the entry with id 2, passing the arguments --bootnum (-b) with the identifier, and --delete-bootnum (-B) to delete the entry:

root #efibootmgr -b 2 -B

Removal

Unmerge

root #emerge --ask --depclean sys-boot/efibootmgr