## arg 1:  the new package version
## arg 2:  the old package version
post_upgrade () {
  # Upgrading from pre-1.4.0: output message about new systemd service.
  if [ $(vercmp "$2" 1.4.0-1) -lt 0 ]; then
    echo "From 1.4.0-1 this package provides a systemd service file at"
    echo "  /usr/lib/systemd/system/jupyterhub.service"
    echo "If you have a custom service in /etc/systemd/system or a"
    echo "similar location, it will continue to be used instead of the"
    echo "service from this package."
  fi

  # Warn about database schema changes.
  if [ $(vercmp "$2" 3.0.0-1) -lt 0 ]; then
    echo "Version 3.0.0 includes a database schema change. You will"
    echo "need to upgrade your database before you can run it."
    echo "See the JupyterHub documentation for details."
  fi
}