A Simple Script to Create systemd-nspawn Alpine Container

I needed a small container for experiments to run on my systemd-based machine. However, LXC and LXD were out of the question. Luckily, systemd has systemd-nspawn tool, which I used to build a container.

The size of the resulting rootfs is around 8.7 MB

Variables to tweak in the script:

• MIRROR: the mirror to download packages from. The full list is available here.
• VERSION: the version of Alpine to install. The full list is available here (as the list of directories)
• if you are neither on x86 nor x86_64, you may need to adjust this line: [ "$(uname -m)" = "x86_64" ] && guestarch="x86_64" || guestarch="x86"

#!/bin/sh -e

MIRROR="http://dl-cdn.alpinelinux.org/alpine"
VERSION="latest-stable"

[ "$(id -u)" -ne "0" ] && echo "You need to be root"   >&2 && exit 1
[ -z "$1" ]            && echo "Usage: $0 destination" >&2 && exit 0

dest="$1"
apkdir="$(mktemp -d)"
[ "$(uname -m)" = "x86_64" ] && guestarch="x86_64" || guestarch="x86"

APKTOOLS="$(wget -q -O - "$MIRROR/$VERSION/main/$guestarch/" | grep -Eo -m 1 '>apk-tools-static[^<]+' | sed 's/[<>]//g')"

wget -q -O - "$MIRROR/$VERSION/main/$guestarch/$APKTOOLS" | tar -xz -C $apkdir || { rm -rf "$apkdir"; exit 1; }
trap 'rm -rf "$apkdir"' EXIT

"$apkdir/sbin/apk.static" -X "$MIRROR/$VERSION/main" -U --arch "$guestarch" --allow-untrusted --root "$dest" --initdb add alpine-base

echo "$MIRROR/$VERSION/main" > "$dest/etc/apk/repositories"
echo "$MIRROR/$VERSION/community" >> "$dest/etc/apk/repositories"

for i in $(seq 0 10); do
    echo "pts/$i" >> "$dest/etc/securetty"
done

sed -i '/tty[0-9]:/ s/^/#/' "$dest/etc/inittab"
echo 'console::respawn:/sbin/getty 38400 console' >> "$dest/etc/inittab"

for svc in bootmisc hostname syslog; do
    ln -s "/etc/init.d/$svc" "$dest/etc/runlevels/boot/$svc"
done

for svc in killprocs savecache; do
    ln -s "/etc/init.d/$svc" "$dest/etc/runlevels/shutdown/$svc"
done

echo "Success"