nixpkgs/nixos/doc/manual/administration/user-sessions.xml

<chapter xmlns="http://docbook.org/ns/docbook"
        xmlns:xlink="http://www.w3.org/1999/xlink"
        xmlns:xi="http://www.w3.org/2001/XInclude"
        version="5.0"
        xml:id="sec-user-sessions">

<title>User Sessions</title>

<para>Systemd keeps track of all users who are logged into the system
(e.g. on a virtual console or remotely via SSH).  The command
<command>loginctl</command> allows querying and manipulating user
sessions.  For instance, to list all user sessions:

<screen>
$ loginctl
   SESSION        UID USER             SEAT
        c1        500 eelco            seat0
        c3          0 root             seat0
        c4        500 alice
</screen>

This shows that two users are logged in locally, while another is
logged in remotely.  (“Seats” are essentially the combinations of
displays and input devices attached to the system; usually, there is
only one seat.)  To get information about a session:

<screen>
$ loginctl session-status c3
c3 - root (0)
           Since: Tue, 2013-01-08 01:17:56 CET; 4min 42s ago
          Leader: 2536 (login)
            Seat: seat0; vc3
             TTY: /dev/tty3
         Service: login; type tty; class user
           State: online
          CGroup: name=systemd:/user/root/c3
                  ├─ 2536 /nix/store/10mn4xip9n7y9bxqwnsx7xwx2v2g34xn-shadow-4.1.5.1/bin/login --
                  ├─10339 -bash
                  └─10355 w3m nixos.org
</screen>

This shows that the user is logged in on virtual console 3.  It also
lists the processes belonging to this session.  Since systemd keeps
track of this, you can terminate a session in a way that ensures that
all the session’s processes are gone:

<screen>
# loginctl terminate-session c3
</screen>

</para>

</chapter>