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b1de39dec8
Logically, this is better, because we're describing a subset of possible return values. Visually this also looks quite good because groff renders refsect2 much less prominently. Also rewrap things, add <constant> in various places, fix some typos.
248 lines
10 KiB
XML
248 lines
10 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1+ -->
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<refentry id="sd_login_monitor_new" conditional='HAVE_PAM'
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_login_monitor_new</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_login_monitor_new</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_login_monitor_new</refname>
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<refname>sd_login_monitor_unref</refname>
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<refname>sd_login_monitor_unrefp</refname>
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<refname>sd_login_monitor_flush</refname>
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<refname>sd_login_monitor_get_fd</refname>
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<refname>sd_login_monitor_get_events</refname>
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<refname>sd_login_monitor_get_timeout</refname>
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<refname>sd_login_monitor</refname>
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<refpurpose>Monitor login sessions, seats, users and virtual machines/containers</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-login.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_new</function></funcdef>
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<paramdef>const char *<parameter>category</parameter></paramdef>
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<paramdef>sd_login_monitor **<parameter>ret</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>sd_login_monitor *<function>sd_login_monitor_unref</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_login_monitor_unrefp</function></funcdef>
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<paramdef>sd_login_monitor **<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_flush</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_get_fd</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_get_events</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_login_monitor_get_timeout</function></funcdef>
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<paramdef>sd_login_monitor *<parameter>m</parameter></paramdef>
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<paramdef>uint64_t *<parameter>timeout_usec</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_login_monitor_new()</function> may be used to
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monitor login sessions, users, seats, and virtual
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machines/containers. Via a monitor object a file descriptor can be
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integrated into an application defined event loop which is woken
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up each time a user logs in, logs out or a seat is added or
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removed, or a session, user, seat or virtual machine/container
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changes state otherwise. The first parameter takes a string which
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can be <literal>seat</literal> (to get only notifications about
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seats being added, removed or changed), <literal>session</literal>
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(to get only notifications about sessions being created or removed
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or changed), <literal>uid</literal> (to get only notifications
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when a user changes state in respect to logins) or
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<literal>machine</literal> (to get only notifications when a
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virtual machine or container is started or stopped). If
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notifications shall be generated in all these conditions,
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<constant>NULL</constant> may be passed. Note that in the future
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additional categories may be defined. The second parameter returns
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a monitor object and needs to be freed with the
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<function>sd_login_monitor_unref()</function> call after
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use.</para>
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<para><function>sd_login_monitor_unref()</function> may be used to
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destroy a monitor object. Note that this will invalidate any file
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descriptor returned by
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<function>sd_login_monitor_get_fd()</function>.</para>
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<para><function>sd_login_monitor_unrefp()</function> is similar to
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<function>sd_login_monitor_unref()</function> but takes a pointer
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to a pointer to an <type>sd_login_monitor</type> object. This call
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is useful in conjunction with GCC's and LLVM's <ulink
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url="https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html">Clean-up
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Variable Attribute</ulink>. Note that this function is defined as
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inline function. Use a declaration like the following, in order to
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allocate a login monitor object that is freed automatically as the
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code block is left:</para>
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<programlisting>{
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__attribute__((cleanup(sd_login_monitor_unrefp)) sd_login_monitor *m = NULL;
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int r;
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…
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r = sd_login_monitor_default(&m);
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if (r < 0)
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fprintf(stderr, "Failed to allocate login monitor object: %s\n", strerror(-r));
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…
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}</programlisting>
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<para><function>sd_login_monitor_flush()</function> may be used to
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reset the wakeup state of the monitor object. Whenever an event
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causes the monitor to wake up the event loop via the file
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descriptor this function needs to be called to reset the wake-up
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state. If this call is not invoked, the file descriptor will
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immediately wake up the event loop again.</para>
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<para><function>sd_login_monitor_unref()</function> and
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<function>sd_login_monitor_unrefp()</function> execute no
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operation if the passed in monitor object is
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<constant>NULL</constant>.</para>
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<para><function>sd_login_monitor_get_fd()</function> may be used
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to retrieve the file descriptor of the monitor object that may be
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integrated in an application defined event loop, based around
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<citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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or a similar interface. The application should include the
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returned file descriptor as wake-up source for the events mask
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returned by <function>sd_login_monitor_get_events()</function>. It
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should pass a timeout value as returned by
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<function>sd_login_monitor_get_timeout()</function>. Whenever a
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wake-up is triggered the file descriptor needs to be reset via
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<function>sd_login_monitor_flush()</function>. An application
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needs to reread the login state with a function like
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<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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or similar to determine what changed.</para>
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<para><function>sd_login_monitor_get_events()</function> will
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return the <function>poll()</function> mask to wait for. This
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function will return a combination of <constant>POLLIN</constant>,
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<constant>POLLOUT</constant> and similar to fill into the
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<literal>.events</literal> field of <varname>struct
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pollfd</varname>.</para>
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<para><function>sd_login_monitor_get_timeout()</function> will
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return a timeout value for usage in <function>poll()</function>.
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This returns a value in microseconds since the epoch of
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<constant>CLOCK_MONOTONIC</constant> for timing out
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<function>poll()</function> in <varname>timeout_usec</varname>.
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See
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<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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for details about <constant>CLOCK_MONOTONIC</constant>. If there
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is no timeout to wait for this will fill in <constant>(uint64_t)
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-1</constant> instead. Note that <function>poll()</function> takes
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a relative timeout in milliseconds rather than an absolute timeout
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in microseconds. To convert the absolute 'µs' timeout into
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relative 'ms', use code like the following:</para>
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<programlisting>uint64_t t;
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int msec;
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sd_login_monitor_get_timeout(m, &t);
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if (t == (uint64_t) -1)
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msec = -1;
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else {
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struct timespec ts;
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uint64_t n;
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clock_gettime(CLOCK_MONOTONIC, &ts);
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n = (uint64_t) ts.tv_sec * 1000000 + ts.tv_nsec / 1000;
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msec = t > n ? (int) ((t - n + 999) / 1000) : 0;
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}</programlisting>
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<para>The code above does not do any error checking for brevity's
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sake. The calculated <varname>msec</varname> integer can be passed
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directly as <function>poll()</function>'s timeout
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parameter.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On success,
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<function>sd_login_monitor_new()</function>,
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<function>sd_login_monitor_flush()</function> and
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<function>sd_login_monitor_get_timeout()</function>
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return 0 or a positive integer. On success,
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<function>sd_login_monitor_get_fd()</function> returns
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a Unix file descriptor. On success,
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<function>sd_login_monitor_get_events()</function>
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returns a combination of <constant>POLLIN</constant>,
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<constant>POLLOUT</constant> and suchlike. On failure,
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these calls return a negative errno-style error
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code.</para>
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<para><function>sd_login_monitor_unref()</function>
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always returns <constant>NULL</constant>.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<varlistentry>
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<term><constant>-EINVAL</constant></term>
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<listitem><para>An input parameter was invalid (out of range, or <constant>NULL</constant>, where
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that is not accepted). The specified category to watch is not known.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><constant>-ENOMEM</constant></term>
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<listitem><para>Memory allocation failed.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect2>
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</refsect1>
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<xi:include href="libsystemd-pkgconfig.xml" />
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-login</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>poll</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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