#!/bin/sh
#
# chroot_wrapper.sh - simplistic wrapper to make chroot more practical
#
# Copyright (C) 2016  Antonio Ospite <ao2@ao2.it>
#
# This program is free software. It comes without any warranty, to
# the extent permitted by applicable law. You can redistribute it
# and/or modify it under the terms of the Do What The Fuck You Want
# To Public License, Version 2, as published by Sam Hocevar. See
# http://sam.zoy.org/wtfpl/COPYING for more details.

set -e

[ "x$1" = "x" ] && { echo "usage: $(basename $0) <NEWROOT> [<COMMAND>]" 1>&2; exit 1; }

NEWROOT="$1"
shift

COMMAND="$@"
[ "x$COMMAND" = "x" ] && COMMAND="/bin/bash"

[ "$(id -u)" = "0" ] || { echo "Run this script as root." 1>&2; exit 1; }

_mount_prereq() {
  mount --bind /dev ${NEWROOT}/dev
  mount --bind /dev/pts ${NEWROOT}/dev/pts
  mount --bind /proc ${NEWROOT}/proc
  mount --bind /sys ${NEWROOT}/sys
  mount --bind /run ${NEWROOT}/run
  mount --bind /tmp ${NEWROOT}/tmp
}

_umount_prereq()
{
  umount ${NEWROOT}/tmp || :
  umount ${NEWROOT}/run || :
  umount ${NEWROOT}/sys || :
  umount ${NEWROOT}/proc || :
  umount ${NEWROOT}/dev/pts || :
  umount ${NEWROOT}/dev || :
}

_mount_prereq
trap '_umount_prereq' 0
trap "exit 2" 1 2 3 15

# Unshare the UTS namespace.
# This ensures that the hostname change affects only the chrooted process.
# WIthout "unshare --uts" the host system hostname would be changed too.
# An alternative way would have been to use a tool like chname:
# http://blog.marineau.org/post/46688543379/giving-chroot-its-own-hostname-chname
unshare --uts chroot ${NEWROOT} /bin/bash -c "hostname -F /etc/hostname && exec ${COMMAND}"