systemd/man/sd-login.xml

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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">

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<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 &lt;systemd/sd-login.h&gt;</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><refentrytitle>sd-readahead</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>