#!/bin/sh
#
# mount device
#

DEVPATH="$(rootdev -s | awk '{ print substr($0, 0, length-1) }')7"

mkdir -p /tmp/a
umount /tmp/a >/dev/null 2>&1

mount "${DEVPATH}"     /tmp/a
mount -o bind /proc    /tmp/a/proc
mount -o bind /dev     /tmp/a/dev
mount -o bind /dev/pts /tmp/a/dev/pts
mount -o bind /sys     /tmp/a/sys
mount -o bind /run     /tmp/a/run

## then
chroot --groups=0 /tmp/a /bin/bash