systemd/man/sd-login.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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  Copyright 2010 Lennart Poettering

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<refentry id="sd-login" conditional='HAVE_PAM'
  xmlns:xi="http://www.w3.org/2001/XInclude">

  <refentryinfo>
    <title>sd-login</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</refentrytitle>
    <manvolnum>3</manvolnum>
  </refmeta>

  <refnamediv>
    <refname>sd-login</refname>
    <refpurpose>APIs for
    tracking logins</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;systemd/sd-login.h&gt;</funcsynopsisinfo>
    </funcsynopsis>

    <cmdsynopsis>
      <command>pkg-config --cflags --libs libsystemd</command>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Description</title>

    <para><filename>sd-login.h</filename> provides APIs to introspect
    and monitor seat, login session and user status information on the
    local system. </para>

    <para>See <ulink
    url="https://www.freedesktop.org/wiki/Software/systemd/multiseat">Multi-Seat
    on Linux</ulink> for an introduction into multi-seat support on
    Linux, the background for this set of APIs.</para>

    <para>Note that these APIs only allow purely passive access and
    monitoring of seats, sessions and users. To actively make changes
    to the seat configuration, terminate login sessions, or switch
    session on a seat you need to utilize the D-Bus API of
    systemd-logind, instead.</para>

    <para>These functions synchronously access data in
    <filename>/proc</filename>, <filename>/sys/fs/cgroup</filename>
    and <filename>/run</filename>. All of these are virtual file
    systems, hence the runtime cost of the accesses is relatively
    cheap.</para>

    <para>It is possible (and often a very good choice) to mix calls
    to the synchronous interface of <filename>sd-login.h</filename>
    with the asynchronous D-Bus interface of systemd-logind. However,
    if this is done you need to think a bit about possible races since
    the stream of events from D-Bus and from
    <filename>sd-login.h</filename> interfaces such as the login
    monitor are asynchronous and not ordered against each
    other.</para>

    <para>If the functions return string arrays, these are generally
    <constant>NULL</constant> terminated and need to be freed by the
    caller with the libc
    <citerefentry project='man-pages'><refentrytitle>free</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    call after use, including the strings referenced therein.
    Similarly, individual strings returned need to be freed, as
    well.</para>

    <para>As a special exception, instead of an empty string array
    <constant>NULL</constant> may be returned, which should be treated
    equivalent to an empty string array.</para>

    <para>See
    <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
    <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>
    for more information about the functions
    implemented.</para>
  </refsect1>

  <xi:include href="libsystemd-pkgconfig.xml" />

  <refsect1>
    <title>See Also</title>
    <para>
      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_pid_get_session</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_uid_get_state</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_session_is_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_seat_get_active</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_get_seats</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd_login_monitor_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
      <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
    </para>
  </refsect1>

</refentry>