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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
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.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<refentry id="sd-login" conditional='HAVE_PAM'
xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd-login</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>sd-login</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd-login</refname>
<refpurpose>APIs for
tracking logins</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo>
</funcsynopsis>
<cmdsynopsis>
<command>pkg-config --cflags --libs libsystemd</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>sd-login.h</filename> provides APIs to introspect
and monitor seat, login session and user status information on the
local system. </para>
<para>See <ulink
url="http://www.freedesktop.org/wiki/Software/systemd/multiseat">Multi-Seat
on Linux</ulink> for an introduction into multi-seat support on
Linux, the background for this set of APIs.</para>
<para>Note that these APIs only allow purely passive access and
monitoring of seats, sessions and users. To actively make changes
to the seat configuration, terminate login sessions, or switch
session on a seat you need to utilize the D-Bus API of
systemd-logind, instead.</para>
<para>These functions synchronously access data in
<filename>/proc</filename>, <filename>/sys/fs/cgroup</filename>
and <filename>/run</filename>. All of these are virtual file
systems, hence the runtime cost of the accesses is relatively
cheap.</para>
<para>It is possible (and often a very good choice) to mix calls
to the synchronous interface of <filename>sd-login.h</filename>
with the asynchronous D-Bus interface of systemd-logind. However,
if this is done you need to think a bit about possible races since
the stream of events from D-Bus and from
<filename>sd-login.h</filename> interfaces such as the login
monitor are asynchronous and not ordered against each
other.</para>
<para>If the functions return string arrays, these are generally
<constant>NULL</constant> terminated and need to be freed by the
caller with the libc
<citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
call after use, including the strings referenced therein.
Similarly, individual strings returned need to be freed, as
well.</para>
<para>As a special exception, instead of an empty string array
<constant>NULL</constant> may be returned, which should be treated
equivalent to an empty string array.</para>
<para>See
<citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
for more information about the functions
implemented.</para>
</refsect1>
<xi:include href="libsystemd-pkgconfig.xml" />
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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