Quick memo to myself: When you abort pacman for some reason while it updates the linux kernel it will not have built a new init ramdisk. The next time you reboot, your kernel will not find any hard disk to boot from!

And because you will mess this up again, here's how to fix it:

• boot into the Arch installer from your USB stick
• mount the disk

  mount /dev/sda3 /mnt

• chroot into it

  chroot /mnt /bin/bash

• mount the virtual file systems

  mount -t proc proc /proc
  mount -t sysfs sys /sys
  mount -t devtmpfs udev /dev

• create the ramdisk

  mkinitcpio -p linux

• reboot

You're welcome, future self.