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<refentry id="sd_seat_get_active" conditional='HAVE_PAM'>

  <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>
    <refname>sd_seat_can_tty</refname>
    <refname>sd_seat_can_graphical</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 int *<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>

      <funcprototype>
        <funcdef>int <function>sd_seat_can_tty</function></funcdef>
        <paramdef>const char *<parameter>seat</parameter></paramdef>
      </funcprototype>

      <funcprototype>
        <funcdef>int <function>sd_seat_can_graphical</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 passed <constant>NULL</constant>,
    in case only one of the parameters shall be queried. The returned
    string needs to be freed with the libc
    <citerefentry project='man-pages'><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 (<constant>NULL</constant> 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. This
    value is the same the return value, if the latter is nonnegative.
    The two arrays and the last parameter may be passed as
    <constant>NULL</constant> 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 project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use. Note that instead of an empty array
    <constant>NULL</constant> 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 (with only one
    being active at a time).</para>

    <para><function>sd_seat_can_tty()</function> may be used to
    determine whether a specific seat provides TTY functionality, i.e.
    is useful as a text console.</para>

    <para><function>sd_seat_can_graphical()</function> may be used to
    determine whether a specific seat provides graphics functionality,
    i.e. is useful as a graphics display.</para>

    <para>If the <varname>seat</varname> parameter of any of these
    functions is passed as <constant>NULL</constant>, 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>
    returns 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>,
    <function>sd_seat_can_tty</function> and
    <function>sd_seat_can_graphical</function> return a positive
    integer, if it fails 0. On failure, these calls return a negative
    errno-style error code.</para>
  </refsect1>

  <refsect1>
    <title>Errors</title>

    <para>Returned errors may indicate the following problems:</para>

    <variablelist>

      <varlistentry>
        <term><constant>-ENODATA</constant></term>

        <listitem><para>The given field is not specified for the described
        seat.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ENXIO</constant></term>

        <listitem><para>The specified seat is unknown.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-EINVAL</constant></term>

        <listitem><para>An input parameter was invalid (out of range,
        or NULL, where that is not accepted).</para></listitem>
      </varlistentry>

      <varlistentry>
        <term><constant>-ENOMEM</constant></term>

        <listitem><para>Memory allocation failed.</para></listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Notes</title>

    <para>The <function>sd_seat_get_active()</function>,
    <function>sd_seat_get_sessions()</function>,
    <function>sd_seat_can_multi_session()</function>,
    <function>sd_seat_can_tty()</function> and
    <function>sd_seat_can_graphical()</function> interfaces are
    available as a shared library, which can be compiled and linked to
    with the
    <constant>libsystemd</constant> <citerefentry project='die-net'><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>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_session_get_seat</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>
