systemd/man/sd_login_monitor_new.xml

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<refentry id="sd_login_monitor_new">

        <refentryinfo>
                <title>sd_login_monitor_new</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_monitor_new</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_login_monitor_new</refname>
                <refname>sd_login_monitor_unref</refname>
                <refname>sd_login_monitor_flush</refname>
                <refname>sd_login_monitor_get_fd</refname>
                <refname>sd_login_monitor</refname>
                <refpurpose>Monitor login sessions, seats and users</refpurpose>
        </refnamediv>

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

                        <funcprototype>
                                <funcdef>int <function>sd_login_monitor_new</function></funcdef>
                                <paramdef>const char* <parameter>category</parameter></paramdef>
                                <paramdef>sd_login_monitor** <parameter>ret</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>sd_login_monitor* <function>sd_login_monitor_unref</function></funcdef>
                                <paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_login_monitor_flush</function></funcdef>
                                <paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
                                <paramdef>sd_login_monitor* <parameter>m</parameter></paramdef>
                        </funcprototype>

                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_login_monitor_new()</function> may
                be used to monitor login session, users and seats. Via
                a monitor object a file descriptor can be integrated
                into an application defined event loop which is woken
                up each time a user logs in, logs out or a seat is
                added or removed, or a session, user, or seat changes
                state otherwise. The first parameter takes a string
                which can be either <literal>seat</literal> (to get
                only notifications about seats being added, removed or
                changed), <literal>session</literal> (to get only
                notifications about sessions being created or removed
                or changed) or <literal>uid</literal> (to get only
                notifications when a user changes state in respect to
                logins). If notifications shall be generated in all
                these conditions, NULL may be passed. Note that in
                future additional categories may be defined. The
                second parameter returns a monitor object and needs to
                be freed with the
                <function>sd_login_monitor_unref()</function> call
                after use.</para>

                <para><function>sd_login_monitor_unref()</function>
                may be used to destroy a monitor object. Note that
                this will invalidate any file descriptor returned by
                <function>sd_login_monitor_get_fd()</function>.</para>

                <para><function>sd_login_monitor_flush()</function>
                may be used to reset the wakeup state of the monitor
                object. Whenever an event causes the monitor to wake
                up the event loop via the file descriptor this
                function needs to be called to reset the wake-up
                state. If this call is not invoked the file descriptor
                will immediately wake up the event loop again.</para>

                <para><function>sd_login_monitor_get_fd()</function>
                may be used to retrieve the file descriptor of the
                monitor object that may be integrated in an
                application defined event loop, based around
                <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                or a similar interface. The application should include
                the returned file descriptor as wake up source for
                POLLIN events. Whenever a wake-up is triggered the
                file descriptor needs to be reset via
                <function>sd_login_monitor_flush()</function>. An
                application needs to reread the login state with a
                function like
                <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                or similar to determine what changed.</para>
        </refsect1>

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

                <para>On success
                <function>sd_login_monitor_new()</function> and
                <function>sd_login_monitor_flush()</function> return 0
                or a positive integer. On success
                <function>sd_login_monitor_get_fd()</function> returns
                a Unix file descriptor. On failure, these calls return
                a negative errno-style error code.</para>

                <para><function>sd_login_monitor_unref()</function>
                always returns NULL.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The <function>sd_login_monitor_new()</function>,
                <function>sd_login_monitor_unref()</function>, <function>sd_login_monitor_flush()</function> and
                <function>sd_login_monitor_get_fd()</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>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>