Change Root
From ArchWiki
"[Changing Root] on Unix operating systems is an operation that changes the apparent disk root directory for the current running process and its children. A program that is re-rooted to another directory cannot access or name files outside that directory, and the directory is called a "chroot jail"..." [Wikipedia].
Changing root is at times necessary to perform various system operations. Examples would be to reinstall GRUB or to reset a forgotten password. Changing root is often done from from a LiveCD or LiveUSB to enter the installation root partition.
Mounting the device
First, the device or partition with the Linux system on it will need to be mounted. To discover the kernel name of the storage device name, type:
fdisk -l
Create a directory where you would like to mount the partition, then mount the device or partition:
mkdir /mnt/arch mount /dev/<device-or-partition-name> /mnt/arch
Changing Root
Before you can chroot be sure that the Linux environment architectures of both the current environment and the environment you wish to enter match (e.g. 32bit LiveCD and 32bit system install). You can find the architecture of your current environment by:
uname -m
If they do, then you will need to mount the temporary filesystems:
mount -t proc none /mnt/arch/proc mount -t sysfs none /mnt/arch/sys mount -o bind /dev /mnt/arch/dev
Now chroot to your installed device or partition and define your shell:
chroot /mnt/arch /bin/bash
If this is a new install and you have yet to enter it, you will need to create an mtab file:
grep -v rootfs /proc/mounts > /etc/mtab
Exiting chroot
First the chroot shell must be exited:
exit
Then unmount the temporary filesystems and mounted devices then reboot:
umount /mnt/arch/{proc,sys,dev} umount /mnt/arch reboot