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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><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>