Creating a debian package that can run with System V, Upstart, or Systemd

We now have a gaggle of ways daemons can be run on linux, and ubuntu in particular. I want my .deb to be installable on a wide range of ubuntu and debian systems, some of them quite old, so here's my solution.

The general idea is to provide files for all three systems, and pick the right one to use at post-install time as described here, but with the added complication that we need systemd as well (for Ubuntu after 15.10, which uses systemd by default).

My postinstall file looks like this:

case "$1" in
  configure)
    ${DAEMON} ${DAEMON_ARGS} "--install"

    if [ -x /sbin/initctl ] && /sbin/initctl version | /bin/grep -q upstart; then
      # Early versions of upstart didn't support restarting a service that
      # wasn't already running:
      # https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/430883
      /usr/sbin/service myservice stop 2>/dev/null || true
      /usr/sbin/service myservice start 2>/dev/null
    elif [ -x /bin/systemctl ]; then
      # Systemd
      /bin/systemctl enable myservice
      /bin/systemctl restart myservice
    elif [ -x "/etc/init.d/myservice" ]; then
      update-rc.d myservice defaults >/dev/null
      invoke-rc.d myservice start || exit $?
    fi

  ;;

  abort-upgrade|abort-remove|abort-deconfigure)
  ;;

  *)
    echo "postinst called with unknown argument \`$1'" >&2
    exit 1
  ;;
esac

If you're using debhelper you need to make sure you're using at least version 9.20130504, when systemd support was added. Then, just like you do for Upstart and System V you need to put your systemd unit file in:

debian/mypackage.service

and it will be copied into

lib/systemd/system/package.service

in the package build directory as described here.