mkchroot

#!/bin/bash

# Creates a chroot environment for the binaries
# passed on the command line, including the NSS
# subsystem, the RTLD and any dynamic libraries
# required by the binaries.  Optionally, copies
# the given configuration files.

# Tested on Ubuntu 12.04 x86-64. Patches welcome.

#  - vjt  Thu Aug 30 16:24:02 CEST 2012

set -e

while true; do
  case $1 in
    -u) USER=$2;
      shift 2 ;;
    -c) CONFS="$CONFS $2"
      shift 2 ;;
    -h) help
      exit -1 ;;
    *) break ;;
  esac
done

help() {
  echo "Usage: $0 -u user [-c conf [-c conf] [...]] binary binary ..."
}

BINARIES=$*
ARCH=$(dpkg-architecture -qDEB_HOST_MULTIARCH)

echo "Creating directory tree..."
mkdir -p bin etc lib tmp
ln -sf lib lib64

echo "Copying NSS subsystem..."
ln -f /lib/$ARCH/libnss_{dns,compat,files}* lib/
ln -f /etc/{{host,nsswitch}.conf,hosts} etc/

# Handle symlinked resolv.conf
if [ -L /etc/resolv.conf ]; then
  link=`readlink /etc/resolv.conf`
  echo $link | grep -q ^/ && resolv=$link ||\
    resolv=`dirname /etc/resolv.conf`/$link
  cp $resolv etc/
else
  ln -f /etc/resolv.conf etc/
fi

echo "Copying the RTLD..."
ld=/lib64/ld-linux-*.so.2
ln -f `readlink $ld` lib/`basename $ld`

echo "Creating passwd/group files..."
grep -E "root|$USER" /etc/passwd > etc/passwd
grep -E "root|`id -g $USER`" /etc/group > etc/group

if [ -n "$CONFS" ]; then
  echo "Copying $CONFS"
  cp $CONFS etc/
fi

for binary in $BINARIES; do
  if [ ! -x $binary ]; then
    echo "Non-executable binary $binary - skipping"
    continue
  fi

  echo "Copying $binary and its libraries..."

  ln -f $binary bin/
  ldd $binary | awk '{print $3}' | grep ^/ | \
    while read lib; do
      ln -f $lib lib/
      ln -f `dirname $lib`/`readlink $lib` lib/
    done

done

bindfs() {
  src=$1
  dst=$2

  echo "Bind-mounting $src into $dst"
  mkdir -p $dst
  if ! grep -q $dst /etc/fstab; then
    cat >>/etc/fstab <<EOF

# Added by mkchroot on `date`
$src $dst none bind
EOF
  fi
  grep -q $dst /proc/mounts || mount $dst
}

root=`realpath .`
bindfs /run $root/var/run
bindfs /usr/share/zoneinfo $root/usr/share/zoneinfo
ln -f /etc/localtime etc/

echo "Done!"