bash-3.2# cat /lib/systemd/system/user\@.service
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

[Unit]
Description=User Manager for %I
After=systemd-user-sessions.service

[Service]
User=%I
PAMName=systemd-user
Type=notify
Environment=SHELL=%s
ExecStart=/lib/systemd/systemd --user --unit=default.target
Environment=DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/%I/dbus/user_bus_socket
Slice=user-%i.slice