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<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
This file is part of systemd.
Copyright 2010 Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
-->
<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 <systemd/sd-login.h></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, &t);
if (t == (uint64_t) -1)
msec = -1;
else {
struct timespec ts;
uint64_t n;
clock_getttime(CLOCK_MONOTONIC, &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>libelogind</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>
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