init.sh

#!/bin/bash

echo $0 $@ $(pwd)
cd "$(dirname "$0")"

mkdir -p rootfs upper squash

./busybox tar xzf utils.tar.gz
./busybox sh -c "utils/squashfuse ./root.sqsh ./squash"
./busybox sh -c "utils/unionfs -o cow upper=RW:squash=RO rootfs"
./busybox sh -c "mkdir ./app ./rootfs/app"

./busybox sh -c "utils/bwrap \
  --bind ./rootfs / \
  --dev-bind /dev /dev \
  --proc /proc \
  --tmpfs /tmp \
  --ro-bind /sys /sys \
  --dir /var/tmp \
  --ro-bind ./app /app \
  --bind /home/$USER/ /home/user/ \
  --ro-bind /sys/block /sys/block \
  --ro-bind /sys/bus /sys/bus \
  --ro-bind /sys/class /sys/class \
  --ro-bind /sys/dev /sys/dev \
  --ro-bind /sys/devices /sys/devices \
  --ro-bind /etc/resolv.conf /etc/resolv.conf \
  --unshare-net \
  --unshare-ipc \
  --unshare-pid \
  --unshare-uts \
  --unshare-cgroup \
  --unshare-all \
  --hostname virt \
  --setenv HOME /home/user \
  --setenv USER user \
  --setenv PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/app \
  --dir /run/user/$(id -u) \
  /bin/bash"

./busybox sh -c "umount ./rootfs"
./busybox sh -c "umount ./squash"

makebin.sh

#!/bin/bash

if [ $# -lt 2 ]; then
    echo "Usage: $0 <init> <files...>"
    exit 1
fi

out=$(mktemp)
init="$1"
shift
files=("$@")

cat > ${out} <<EOF
#!/bin/bash

PAYLOAD_LINE=__PAYLOAD_LINE__

TEMP_DIR=\$(mktemp -d)

cleanup() {
    rm -rf "\$TEMP_DIR"
}
trap cleanup EXIT

tail -n +\$PAYLOAD_LINE "\$0" | tar x -C "\$TEMP_DIR"

chmod +x "\$TEMP_DIR/${init}"

cd \$TEMP_DIR

EXTRACTED="\$TEMP_DIR" "\$TEMP_DIR/${init}" "\$@"

exit 0

EOF

echo "## DATA ##" >> ${out}

tar cvf - "$init" "${files[@]}" >> ${out}

payload_line=$(grep -n '^## DATA ##' -oa ${out} | cut -d: -f1)
payload_line=$((payload_line + 1))

sed -i "s/PAYLOAD_LINE=__PAYLOAD_LINE__/PAYLOAD_LINE=${payload_line}/" ${out}

cat ${out};
rm ${out}