Bootloaders

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Revision as of 22:42, 31 January 2020 by Leo (talk | contribs) (Installing)
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By default Alpine uses Syslinux as bootloader. This page shows the basic steps you need to perform, if you for any reason want to switch bootloaders or apply some manual configuration.


Installing Syslinux

If you want to switch from another bootloader back to Syslinux, or if you for some reason want to install Syslinux manually, the following steps are required.

Install the syslinux package:

apk add syslinux

If you're using GPT partitions, install the GPT MBR onto the drive you want to install the bootloader on (in this case /dev/sda):

dd bs=440 count=1 conv=notrunc if=/usr/share/syslinux/gptmbr.bin of=/dev/sda

Or if you're using DOS partitions, install the DOS MBR instead:

dd bs=440 count=1 conv=notrunc if=/usr/share/syslinux/mbr.bin of=/dev/sda


Next install the required Syslinux binaries. Despite being called extlinux, Syslinux supports booting from FAT12/16/32, NTFS, ext2/3/4, Btrfs, XFS, and UFS/FFS filesystems.

extlinux --install /boot

The configuration file is located in /boot/extlinux.conf. Alpine ships with a script called update-extlinux which automatically (re)generates this file, for example on updates to Syslinux. The settings for this script can be found in /etc/update-extlinux.conf, including the option to disable automatic overwriting of /boot/extlinux.conf. You can also place additional menu entries in the /etc/update-extlinux.d/ directory, e.g. for dual booting.


EFI

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Todo: Work in progress. This should at least get you started.


Assuming /mnt is a FAT32 partition of type EF00 and /boot belongs to the rootfs created after running setup-disk:

mkdir -p /mnt/EFI/syslinux
cp /usr/share/syslinux/efi64/* /mnt/EFI/syslinux/
cp /boot/extlinux.conf /mnt/EFI/syslinux/syslinux.cfg
cp /boot/vmlinuz* /mnt/
cp /boot/initramfs* /mnt/

You may need to modify /mnt/EFI/syslinux/syslinux.cfg to change the paths to absolute paths (just add a / in front of the vmlinuz/initramfs entries), or copy the files to /mnt/EFI/syslinux instead (XXX: untested).

GRUB

To install GRUB in BIOS mode, (optionally) remove the Syslinux package and install the required GRUB packages:

apk del syslinux
apk add grub grub-bios

For EFI, install Grub's EFI package instead. Note that /boot has to be an EFI compatible filesystem like FAT32.

apk add grub-efi

Next install the MBR and GRUB binaries to disk for BIOS mode:

grub-install /dev/vda

For EFI mode:

grub-install --target=x86_64-efi --efi-directory=/boot

GRUB ships with an automatic config generator, including some automatic detection of other operating systems installed on the device:

grub-mkconfig -o /boot/grub/grub.cfg

This script can be configured via the /etc/default/grub file. See [1] for a list of available options.

systemd-boot

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Todo: Work in progress. This is very short and doesn't cover a lot of the options.


Systemd-boot is the simple EFI bootloader part of the systemd project. It is also available in the Alpine Linux testing repository as a standalone component.

Installing

To install the systemd-boot, enable the testing repository, and install the systemd-boot package. Then make sure the boot and EFI partitions are mounted as read-write and install the bootloader with bootctl.

# apk add systemd-boot
# bootctl install

The bootctl binary also has support for checking if the bootloader is installed.

# bootctl is-installed
yes

Configuring

Example configuration files for alpine are available on /usr/share/systemd/bootctl as loader.conf and alpine.conf.

The bootloader (not the boot entries) can be configured via the loader.conf file, an example is available in /usr/share/systemd/bootctl/loader.conf.

# cp /usr/share/systemd/bootctl/loader.conf /boot/loader
# vi /boot/loader/loader.conf

systemd-boot makes use of configuration files in /boot/loader/entries to list entries for different OSes it can boot into. An example file for Alpine Linux is present on /usr/share/systemd/bootctl/alpine.conf.

# cp /usr/share/systemd/bootctl/alpine.conf /boot/loader/entries
# vi /boot/loader/entries/alpine.conf

The example file has a skeleton structure that requires minimal modifications to make them work. You need to modify the example file to fit your oeprating system, among them:

  • Replace root=UUID=XXXX with the UUID of the root partition.
  • Replace rootfstype with the filesystem used for the root filesystem.
  • Add boot options required/recommended for booting your operating system (E.g: cryptdm=, cryptroot=, modules=, etc).
  • (If you don't use the default linux-lts kernel) Replace vmlinuz-lts and initramfs-lts with the ones that are used.
  • (If you use an Intel CPU and need Intel microcode) add initrd /intel-ucode.img before the initrd call for the initramfs

All the options available are documented in the systemd boot loader specification under Technical Details.

Updating

When the systemd-boot package is updated then the bootloader installed needs to be updated as well:

# bootctl update

Removing

If for any reason you wish to not use systemd-boot anymore then the bootctl binary also provides a command for easily removing the files that were installed with the install command:

# bootctl remove
# apk del systemd-boot

External Links