systemd/man/sd_login_monitor_new.xml

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

        <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_get_events</refname>
                <refname>sd_login_monitor_get_timeout</refname>
                <refname>sd_login_monitor</refname>
                <refpurpose>Monitor login sessions, seats, users and virtual machines/containers</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>

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

                        <funcprototype>
                                <funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
                                <paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
                                <paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
                        </funcprototype>

                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_login_monitor_new()</function> may
                be used to monitor login sessions, users, seats, and
                virtual machines/containers. 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, seat or virtual machine/container
                changes state otherwise. The first parameter takes a
                string which can be <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), <literal>uid</literal> (to get only
                notifications when a user changes state in respect to
                logins) or <literal>machine</literal> (to get only
                notifications when a virtual machine or container is
                started or stopped). If notifications shall be
                generated in all these conditions, <constant>NULL</constant> may be
                passed. Note that in the 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 the
                events mask returned by
                <function>sd_login_monitor_get_events()</function>. It
                should pass a timeout value as returned by
                <function>sd_login_monitor_get_timeout()</function>. 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>

                <para><function>sd_login_monitor_get_events()</function>
                will return the <function>poll()</function> mask to
                wait for. This function will return a combination of
                <constant>POLLIN</constant>, <constant>POLLOUT</constant>
                and similar to fill into the
                <literal>.events</literal> field of <varname>struct
                pollfd</varname>.</para>

                <para><function>sd_login_monitor_get_timeout()</function>
                will return a timeout value for usage in
                <function>poll()</function>. This returns a value in
                microseconds since the epoch of <constant>CLOCK_MONOTONIC</constant>
                for timing out <function>poll()</function> in
                <varname>timeout_usec</varname>. See
                <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                for details about
                <constant>CLOCK_MONOTONIC</constant>. If there is no
                timeout to wait for this will fill in
                <constant>(uint64_t) -1</constant> instead. Note that
                <function>poll()</function> takes a relative timeout
                in milliseconds rather than an absolute timeout in
                microseconds. To convert the absolute 'us' timeout into
                relative 'ms', use code like the following:</para>

                <programlisting>uint64_t t;
int msec;
sd_login_monitor_get_timeout(m, &amp;t);
if (t == (uint64_t) -1)
        msec = -1;
else {
        struct timespec ts;
        uint64_t n;
        clock_getttime(CLOCK_MONOTONIC, &amp;ts);
        n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
        msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
}</programlisting>

                <para>The code above does not do any error checking
                for brevity's sake. The calculated <varname>msec</varname>
                integer can be passed directly as
                <function>poll()</function>'s timeout
                parameter.</para>
        </refsect1>

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

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

                <para><function>sd_login_monitor_unref()</function>
                always returns <constant>NULL</constant>.</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>,
                <function>sd_login_monitor_get_fd()</function>,
                <function>sd_login_monitor_get_events()</function> and
                <function>sd_login_monitor_get_timeout()</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_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>