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Alpine boot menu

by Alejandro Liu

Updated: 2024-03-19

in 2023

tagged alpine, boot, configuration, device, drive, filesystem, linux, network, partition, speed

This article is an update to my Alpine Boot Switcher article.

Contents:

The weakness of that approach was that you needed to be on a running system to select the active kernel. So, if you switched to a broken kernel then you wouldn't be able to revert back without having to get the media device out and modifying the file system to switch to a different kernel.

The approach described here makes use of syslinux or grub menu system to allow you to select a new kernel. It requires modifying the init script in the initramfs image so that you can specifically select the right APK boot repository otherwise it will use the first one found in the boot file system.

This solution is suitable for physical and virtualized systems using BIOS and UEFI boot methods.

The high level approach is:

  • prepare a bootable USB or virtual disk image.
  • during system operation, use the inst_iso script to install a new Alpine release.
  • You can use the mkmenu script to select the new kernel or ...
  • Re-boot the system, syslinux (on BIOS systems) or grub (on UEFI) systems will show a menu to let you select the boot kernel or boot a default kernel after 10 seconds (unless configured for a different time-out).
  • If the boot was succesful, you can use mkmenu to make the current kernel the default kernel.
  • If the boot fails, then you can hard boot the system and use the boot menu to select a known working kernel.

Preparing boot device

Use the mkuub script to create a bootable USB drive or a bootable disk image.

The USB drive can be used on a physical system and supports UEFI and BIOS boot methods (BIOS boot is untested).

The bootable disk image is meant to be used on a virtualized environment. I have tested it on virsh on kvm and uses the BIOS boot method. It has UEFI boot support files but I have not tested this.

Usage:

    ./mkuusb.sh [options] isofile [usbdev]

Options:

  • --serial : Enable serial console
  • --ovl=ovlfile : overlay file to use
  • --boot-label=label : boot partition label
    Defaults to a random label unless ovl is specifed. In that case, it will take the label from the filesystem mounted as /media/boot from /etc/fstab.
  • --boot-size=size : boot partition size
    If not specified it will default to the entire drive or up to half the drive (if data partition is enabled) up to 8GB.
  • --data : create a data partition
  • --data-label=label : label for data partition_disc
    Defaults to a random label unless ovl is specifed then will take the label from the filesystem mounted as /media/data from /etc/fstab.
  • --data-size=size : data partition size
    size defaults to the remaining of the disk
  • isofile: ISO file to use as the base alpine install
  • usbhdd : /dev/path to the thumb drive that will be installed.
    It will try to use a suitable default by looking an unused drive from the currently connected drives on the system. Otherwise a target image file can be specified using:
    • img:path/to/image/file[,size]

if --serial was used, the boot menu will be configure to use the first serial port (Usually COM1) with a speed of 115200. So you can use a serial console or the normal display to select the desired kernel.

When configured using serial, kernel boot message would be displayed on the serial console.

Booting the system

After creating the boot device, you can connected to a physical server or in the case of a bootable image add it to a virtual machine configuration.

Booting the system will show a boot menu letting you select a kernel. If nothing is selected after the time-out period, a configured default will be used.

Adding a new kernel

During normal operation, you may want to upgrade to a new kernel. To do this you can use the script:

  • $bootmedia/scripts/inst_iso.sh file-or-url

You can pass a iso file name or the URL of an ISO over the network. If using an URL, the script will download the image first.

This will prepare the environment to include the new kernel and add a menu entry to boot the new kernel. The default kernel remains as the currently running kernel.

At this point, the system can be rebooted. You can then use the boot menu to select the latest kernel manually.

If the new kernel fails to boot succesfully, then you may need to hard boot the system.

Since the default kernel was not changed, it should boot to the last working kernel and proceed normally.

After a succesful reboot

If the new kernel was succesfully booted, you can use the command:

  • $bootmedia/mkmenu.sh

to make the currently running kernel the default.

Alternative workflow

Alternatively, after the new kernel is installed, you can use the command:

  • $bootmedia/mkmenu.sh --latest

to make the new kernel the default one. You can then re-boot the system and if everything goes fine, you are done.

If the system fails to boot then you probably will need to do a hard boot of the system and use the boot menu to select a working Alpine Linux kernel.

After a succesful boot, then you can use the command:

  • $bootmedia/mkmenu.sh

To make the current running kernel the default.

Removing installed kernels

Alpine Linux boot images are installed in their own folders. If you want to remove a kernel, just remove the folder that you want to un-install and run mkemnu.sh again to update the boot menu.

Downloads

The code can be found in my repository:

Alpine Linux boot images: