#!/bin/bash
# Generate a very minimal filesystem based on busybox-static,
# and load it into the local docker under the name "docker-ut".

missing_pkg() {
    echo "Sorry, I could not locate $1"
    echo "Try 'apt-get install ${2:-$1}'?"
    exit 1
}

BUSYBOX=$(which busybox)
[ "$BUSYBOX" ] || missing_pkg busybox busybox-static
SOCAT=$(which socat)
[ "$SOCAT" ] || missing_pkg socat

shopt -s extglob
set -ex
ROOTFS=`mktemp -d /tmp/rootfs-busybox.XXXXXXXXXX`
trap "rm -rf $ROOTFS" INT QUIT TERM
cd $ROOTFS

mkdir bin etc dev dev/pts lib proc sys tmp
touch etc/resolv.conf
cp /etc/nsswitch.conf etc/nsswitch.conf
echo root:x:0:0:root:/:/bin/sh > etc/passwd
echo root:x:0: > etc/group
ln -s lib lib64
ln -s bin sbin
cp $BUSYBOX $SOCAT bin
for X in $(busybox --list)
do
    ln -s busybox bin/$X
done
rm bin/init
ln bin/busybox bin/init
cp -P /lib/x86_64-linux-gnu/lib{pthread*,c*(-*),dl*(-*),nsl*(-*),nss_*,util*(-*),wrap,z}.so* lib
cp /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 lib
cp -P /usr/lib/x86_64-linux-gnu/lib{crypto,ssl}.so* lib
for X in console null ptmx random stdin stdout stderr tty urandom zero
do
    cp -a /dev/$X dev
done

tar -cf- . | docker import - docker-ut
docker run -i -u root docker-ut /bin/echo Success.
rm -rf $ROOTFS