OpenWRT chroot helper script

chroot.sh

#!/bin/bash

# script to mount and chroot into a rootfs directory
# designed for openwrt systems, but should work for anything with minimal modifications
# unless you specify a different chroot dir,
# place script on the same level as the rootfs directory, should look something like so:

# /mnt/
# |- chroot.sh
# |- rootfs/
#    |- bin/
#    |- etc/
#      [...]

# usage is same as regular chroot command - no args implies 'chroot ./rootfs/ /bin/bash'

DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"

if [ $# -ge 1 ]
  then
    ROOTFS="$1"
  else
    ROOTFS="${DIR}/rootfs"
fi

if [ $# -lt 2 ]
  then
    ARGS="/bin/bash"
  else
    ARGS="${@:2}"
fi

{
  { mount | grep -e "on ${DIR} .*noexec"; } && mount ${DIR} -o exec,remount
  { mount | grep "on ${ROOTFS}/proc";     } || mount -t proc proc ${ROOTFS}/proc/
  { mount | grep "on ${ROOTFS}/sys";      } || mount -t sysfs sys ${ROOTFS}/sys/
  { mount | grep "on ${ROOTFS}/tmp";      } || mount -o bind /tmp ${ROOTFS}/tmp/ 
  { mount | grep "on ${ROOTFS}/dev";      } || mount -o bind /dev ${ROOTFS}/dev/  
  { mount | grep "on ${ROOTFS}/dev/pts";  } || mount -t devpts /dev/pts ${ROOTFS}/dev/pts/  
  cp /etc/resolv.conf ${ROOTFS}/etc/resolv.conf
} >/dev/null 2>&1

chroot ${ROOTFS} ${ARGS}