10-21-2021, 12:47 AM
What do you mean by junk files and what kind of failure do you mean? I don't think pacman writes any temporary files that keep lingering on the system somewhere. It does however cache downloaded packages (in /var/chache/pacman/pkg/), but for a reason. Check out the Arch wiki for more details and instructions on how to clean the cache. After a failed update, just try updating again. It might be another problem if the update was interrupted by external causes like power loss.