When things go wrong to the point where recovering from the operating system is not possible chroot may the only practical way to recover a broken system. Chroot or change root gives access to otherwise inaccessible system and allows execution of commands within the system. To chroot into the system you will first need to Boot Arch Linux from USB or CD.
Find the system partitions that you will need to mount.
Create a directory to mount the root partition.
Mount the root partition.
mount /dev/sda1 /mnt/arch
Mount any other system partitions.
mount /dev/sda2 /mnt/arch/boot mount /dev/sda3 /mnt/arch/home
You may just have one partition or several additional partitions like
Change current directory to the new system directory.
Mount the virtual file systems.
mount -t proc /proc proc/ mount --rbind /sys sys/ mount --rbind /dev dev/
-t proc option sets the type in this case it is
--rbind argument forces to mount recursively meaning all sub-directories will also be mounted. The
/dev arguments specifies the
device that is to be mounted.
dev/ sets the the directory where the device is to be mounted.
Enter chroot environment.
The first argument is the mounted root directory of the system.
At this point you should be able to run commands to diagnose or fix problems like “Unable to find root device” Error. If something didn’t quite work as expected you may need to refer to additional documentation such as change root Arch Linux wiki.