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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"

"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

<refentry id="sd-login" conditional='HAVE_PAM'>

<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 &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>

</funcsynopsis>

<cmdsynopsis>

<command>pkg-config --cflags --libs libsystemd-login</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><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>

call after use, including the strings referenced

therein. Similar, 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>

<refsect1>

<title>Notes</title>

<para>These APIs are implemented as shared library,

which can be compiled and linked to with the

<constant>libsystemd-login</constant>

<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

file.</para>

</refsect1>

<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><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry>,

<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>

</para>

</refsect1>

</refentry>