Cannot start archlinux after update: Cannot find uuid

I just forgot mount boot (thank you, jasonwryan).

The solution to this problem, in my case was:

1. Use a livecd to mount all partitions and use chroot.

2. Update:

   pacman -Syu

3. Regenerate initramfs using:

   mkinitcpio -p linux

4. If you use grub:

   grub-mkconfig -o /mnt/boot/grub/grub.cfg

5. Restart.