systemd/man/sd_seat_get_active.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_seat_get_active">

        <refentryinfo>
                <title>sd_seat_get_active</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_seat_get_active</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_seat_get_active</refname>
                <refname>sd_seat_get_sessions</refname>
                <refname>sd_seat_can_multi_session</refname>
                <refpurpose>Determine state of a specific seat</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>

                        <funcprototype>
                                <funcdef>int <function>sd_seat_get_active</function></funcdef>
                                <paramdef>const char* <parameter>seat</parameter></paramdef>
                                <paramdef>char** <parameter>session</parameter></paramdef>
                                <paramdef>uid_t* <parameter>uid</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_seat_get_sessions</function></funcdef>
                                <paramdef>const char* <parameter>seat</parameter></paramdef>
                                <paramdef>char*** <parameter>sessions</parameter></paramdef>
                                <paramdef>uid_t** <parameter>uid</parameter></paramdef>
                                <paramdef>unsigned* <parameter>n_uids</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_seat_can_multi_session</function></funcdef>
                                <paramdef>const char* <parameter>seat</parameter></paramdef>
                        </funcprototype>
                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_seat_get_active()</function> may be
                used to determine which session is currently active on
                a seat, if there is any. Returns the session
                identifier and the user identifier of the Unix user
                the session is belonging to. Either the session or the
                user identifier parameter can be be passed NULL, in
                case only one of the parameters shall be queried. The
                returned string needs to be freed with the libc
                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                call after use.</para>

                <para><function>sd_seat_get_sessions()</function> may
                be used to determine all sessions on the specified
                seat. Returns two arrays, one (NULL terminated) with
                the session identifiers of the sessions and one with
                the user identifiers of the Unix users the sessions
                belong to. An additional parameter may be used to
                return the number of entries in the latter array. The
                two arrays and the latter parameter may be passed as
                NULL in case these values need not to be
                determined. The arrays and the strings referenced by
                them need to be freed with the libc
                <citerefentry><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                call after use. Note that instead of an empty array
                NULL may be returned and should be considered
                equivalent to an empty array.</para>

                <para><function>sd_seat_can_multi_session()</function>
                may be used to determine whether a specific seat is
                capable of multi-session, i.e. allows multiple login
                sessions in parallel (whith only one being active at a
                time).</para>

                <para>If the <literal>seat</literal> parameter of any
                of these functions is passed as NULL the operation is
                executed for the seat of the session of the calling
                process, if there is any.</para>
        </refsect1>

        <refsect1>
                <title>Return Value</title>

                <para> On success
                <function>sd_seat_get_active()</function> return
                return 0 or a positive integer. On success
                <function>sd_seat_get_sessions()</function> returns
                the number of entries in the session identifier
                array. If the test succeeds
                <function>sd_seat_can_multi_session</function> returns
                a positive integer, if it fails 0. On failure, these
                calls return a negative errno-style error code.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_seat_get_active()</function>,
                <function>sd_seat_get_sessions()</function>, and
                <function>sd_seat_can_multi_session()</function> interfaces
                are available as shared library, which can be compiled
                and linked to with the
                <literal>libsystemd-login</literal>
                <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-login</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_session_get_seat</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>