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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>