Recoving Arch Linux Failed System Upgrade

Once in a while, it's nice to do a complete system upgrade in Arch Linux. All the packages will be updated to the latest bleeding edge release.

However, if for some reason the package upgrade failed, perhaps due to power outage or something unexpected. In my case, I left my system upgrading over night, and unfortunately, in the morning the screen is all black and nothing works. I tried rebooting, but even GRUB didn't show up!

Upgrading arch system

# Beware this might take a long time to run. Could be a few hours. sudo pacman -Syu

Fixing Corrupted Upgrade

1. Boot to Ubuntu live CD
2. Figure out partition where your Arch is installed
sudo fdisk -l
3. Mount the partition
sudo mount /dev/sdaX /mnt
4. Mount devices
mount -t proc /proc mnt/proc
mount --rbind /sys mnt/sys
mount --rbind /dev mnt/dev
5. Chroot to Arch, this basically is to get into Arch system using the current Ubuntu's kernel
sudo chroot /mnt
6. Now that you're inside of your Arch, you can do whatever needed to fix your installation. Below are some stuffs that might be needed
# Finish unfinished Arch upgrade.
# To see if you need this, check /var/log/pacman.log. There you'll see what happened on your last upgrade. (i.e. upgrade got interrupted in the middle) sudo pacman -Syu

# Re-create RAM disk, this creates device initialization configuration that kernel uses to boot
# For more info: https://wiki.archlinux.org/index.php/mkinitcpio
sudo mkinitcpio -p linux

# Fix GRUB installation. In my case, GRUB didn't show up on boot, so perhaps it was corrupted or something
sudo grub-mkconfig > /boot/grub.cfg # Unlike in normal environment, /boot here is mounted as RW, so write here will persist
# P.S: If you dual boot Arch with other distro, mount the other distro before running grub-mkconfig. If you do so
# GRUB will automatically detect it and create appropriate entry in bootloader

7. Reboot your system! :)
Hopefully this is helpful. Much thanks to Mort Yao's article: https://www.soimort.org/notes/170407/