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Sometimes after an update, my Arch linux install will no longer boot properly. This is usually because mkinitcpio failed or the GRUB config needed to be regenerated. This can be fixed by mounting the install with a archlinux-chroot however because I use btrfs with subvolumes, the process is a little different. This post mostly serves as a guide in order to help me out in the future and anyone else who has the same problem.

Note: This guide is written with the assumption that you have basic knowledge of the Linux command line and directory structure.

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Mounting steps

Firstly flash an Arch ISO to a USB stick and boot into it from your BIOS. Personally I like to just keep one around just incase this happens.

Once you have booted into the ISO, use lsblk to list the volumes and partitions available to your system. Find the partition that your system is installed on. It should look something like /dev/sda1 or /dev/nvme0n1p1.

Then you have to mount the drives. If you have subvolumes then this is slightly different. If you don't then you can get away with doing this normally. The subvolume mount steps are below:

mount -o subvol=@ /dev/yourPartition /mnt/
mount -o subvol=@log /dev/yourPartition /mnt/var/log
mount -o subvol=@home /dev/yourPartition /mnt/home
mount -o subvol=@pkg /dev/yourPartition /mnt/var/cache/pacman/pkg

If the boot volume is on a separate partition then you have to mount that as well:

mount /dev/yourBootPartition /mnt/boot

You can ignore the "snapshots" volume.

Then you can chroot into the images and perform the subsequent steps to repair your system.

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Repair steps

If you know what you have to do to repair your system, you can skip this part.

Firstly chroot into the system in order to repair it:

arch-chroot /mnt

Then run the commands to repair the system. These may be different for you, however for me it consists of rerunning mkinitcpio and grub-mkconfig in order.

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

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Conclusion

Hopefully this helps you fix your system.

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