Fixing a broken system

If you performed a partial upgrade, and the system is broken enough that you are unable to run pacman, boot using a monthly Arch ISO from a USB flash drive, an optical disc or a network with PXE. (Don't follow any of the rest of the installation guide.)

Mount your root filesystem:

[ISO] # mount /dev/rootFilesystemDevice /mnt

Mount any other partitions that you created separately, adding the prefix /mnt to all of them, i.e.:

[ISO] # mount /dev/bootDevice /mnt/boot

Try using your system's pacman:

[ISO] # arch-chroot /mnt
[chroot] # pacman -Syu

If that fails, exit the chroot, and try:

[ISO] # pacman -Syu --sysroot /mnt

If that fails, try:

[ISO] # pacman -Syu --root /mnt --cachedir /mnt/var/cache/pacman/pkg