The install script didn't correctly setup which drive to mount as root (
/). Maybe something is very broken with your installation maybe it is this one thing. If it's just this, then you can try to fix it manually...
Most partitions are configured inside
/etc/fstab but the root partition's information is copied elsewhere. That's because
/etc/fstab is stored on root and so this file can't be read until root's been mounted.
Most Linux distributions let you change the root partition during boot by setting the
ROOT=... kernel parameter:
Boot your broken system to the point it drops into the emergency shell.
Inside the emergency shell, use the commands
blkid to list partitions. Work out which one is your root partition. If you followed the installation guide this should be
Reboot and when you get to the grub menu, move up / down to "Black Archlinux" and press e. This will let you edit the boot entry.
Carefully look through to find the line starting
linux. It's usually a very long line an may have been wrapped (continued to the next line). Check this line to see if there is already an option starting
root=. If there is then edit it to the partition you found in step 1. If not then add the option.
Boot your system by pressing ctrlx.
Fixing your system once it's booted
/etc/fstab to correct the entry for
/ if it's wrong. Even if you didn't use the "UUID" in the steps above, this time you should do so. You can again use blkid and lsblk to find the partition.
Make sure your grub boot entries are up to date by running:
Make sure your initramfs is up to date by running:
sudo update-initramfs -uk all
Hopefully this should leave you with a fully bootable system.