How to repair a broken boot parition in Arch Linux

I recently broke the Arch Linux installation of my laptop by running a system update on low battery. A recipe for disaster, I know. The laptop ran out of battery while updating the kernel, so I got propped with this threatening message from the bootloader after trying to boot it up again:

1error: file '/boot/vmlinuz-linux' not found.
2
3Entering rescue mode...
4
5grub rescue>

This happens because the system crashed while updating the kernel, causing the vmlinuz image in the boot partition to be missing or corrupted. Here are the steps I followed to repair the boot sequence using my Arch recovery USB. I will probably need them in the future. These steps have also been useful when repairing a /boot partition that has run out of space.

Recovery Cheat Sheet

Step 1: Wifi Connection

This will be needed for pacman to locate the mirrors and correctly update the system. I recommend using iwd.

Launch the control utility:

1iwctl

Then, inside the utility, check device name:

1[iwd]# device list

Then, start scanning on your station. I will use wlan0 as an example station name:

1[iwd]# station wlan0 scan

And list the networks found:

1[iwd]# station wlan0 get-networks

Finally connect to your network:

1[iwd]# station wlan0 connect <your_network>

You should now be able to ping a website:

1ping www.google.com

Step 2: Chroot into your Filesystem

Start by discovering the name of your partition. We will use /dev/nvme0n1p2 as an example:

1lsblk
2
3NAME             MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
4nvme0n1          259:0    0 476.9G  0 disk 
5├─nvme0n1p1      259:1    0   512M  0 part /boot
6└─nvme0n1p2      259:2    0 476.4G  0 part /

We then need to mount both the filesystem and the /boot partition:

1mount /dev/nvme0n1p2 /mnt
2mount /dev/nvme0n1p1 /mnt/boot

We can then chroot into the environment:

1arch-chroot /mnt

Step 3: Repair the installation

We start by removing the pacman lock left by the unfinished update:

1rm /var/lib/pacman/db.lck

Then we can run the update again to ensure all packages are consistent:

1pacman -Syu

We can then reinstall the kernel:

1sudo pacman -S linux

Finally, just to be safe, we can rebuild initramfs, which will repair the boot environment:

1mkinitcpio -P

Optional: Refresh the bootloader config

This step is needed when repairing fully the boot partition due to a broken bootloader. We start by ensuring that the grub package is installed:

1pacman -S grub

Then we can reinstall grub and regenerate the configuration:

1grub-install --target=x86_64-efi --efi-directory=/boot --bootloader-id=GRUB
2grub-mkconfig -o /boot/grub/grub.cfg

Final Step: Exit and reboot

1exit 
2umount /mnt
3reboot

After rebooting, grub should start normally.