man/sd_watchdog_enabled.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7 -->
   8
   9 <refentry id="sd_watchdog_enabled"
  10   xmlns:xi="http://www.w3.org/2001/XInclude">
  11
  12   <refentryinfo>
  13     <title>sd_watchdog_enabled</title>
  14     <productname>elogind</productname>
  15
  16     <authorgroup>
  17       <author>
  18         <contrib>Developer</contrib>
  19         <firstname>Lennart</firstname>
  20         <surname>Poettering</surname>
  21         <email>lennart@poettering.net</email>
  22       </author>
  23     </authorgroup>
  24   </refentryinfo>
  25
  26   <refmeta>
  27     <refentrytitle>sd_watchdog_enabled</refentrytitle>
  28     <manvolnum>3</manvolnum>
  29   </refmeta>
  30
  31   <refnamediv>
  32     <refname>sd_watchdog_enabled</refname>
  33     <refpurpose>Check whether the service manager expects watchdog keep-alive notifications from a service</refpurpose>
  34   </refnamediv>
  35
  36   <refsynopsisdiv>
  37     <funcsynopsis>
  38       <funcsynopsisinfo>#include &lt;elogind/sd-daemon.h&gt;</funcsynopsisinfo>
  39
  40       <funcprototype>
  41         <funcdef>int <function>sd_watchdog_enabled</function></funcdef>
  42         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  43         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  44       </funcprototype>
  45     </funcsynopsis>
  46   </refsynopsisdiv>
  47
  48   <refsect1>
  49     <title>Description</title>
  50     <para><function>sd_watchdog_enabled()</function> may be called by
  51     a service to detect whether the service manager expects regular
  52     keep-alive watchdog notification events from it, and the timeout
  53     after which the manager will act on the service if it did not get
  54     such a notification.</para>
  55
  56     <para>If the <varname>$WATCHDOG_USEC</varname> environment
  57     variable is set, and the <varname>$WATCHDOG_PID</varname> variable
  58     is unset or set to the PID of the current process, the service
  59     manager expects notifications from this process. The manager will
  60     usually terminate a service when it does not get a notification
  61     message within the specified time after startup and after each
  62     previous message. It is recommended that a daemon sends a
  63     keep-alive notification message to the service manager every half
  64     of the time returned here. Notification messages may be sent with
  65     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  66     with a message string of <literal>WATCHDOG=1</literal>.</para>
  67
  68     <para>If the <parameter>unset_environment</parameter> parameter is
  69     non-zero, <function>sd_watchdog_enabled()</function> will unset
  70     the <varname>$WATCHDOG_USEC</varname> and
  71     <varname>$WATCHDOG_PID</varname> environment variables before
  72     returning (regardless of whether the function call itself
  73     succeeded or not). Those variables are no longer inherited by
  74     child processes. Further calls to
  75     <function>sd_watchdog_enabled()</function> will also return with
  76     zero.</para>
  77
  78     <para>If the <parameter>usec</parameter> parameter is non-NULL,
  79     <function>sd_watchdog_enabled()</function> will write the timeout
  80     in µs for the watchdog logic to it.</para>
  81
  82     <para>To enable service supervision with the watchdog logic, use
  83     <varname>WatchdogSec=</varname> in service files. See
  84     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  85     for details.</para>
  86
  87     <para>Use
  88     <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  89     to enable automatic watchdog support in
  90     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>-based event loops.</para>
  91   </refsect1>
  92
  93   <refsect1>
  94     <title>Return Value</title>
  95
  96     <para>On failure, this call returns a negative errno-style error
  97     code. If the service manager expects watchdog keep-alive
  98     notification messages to be sent, &gt; 0 is returned, otherwise 0
  99     is returned. Only if the return value is &gt; 0, the
 100     <parameter>usec</parameter> parameter is valid after the
 101     call.</para>
 102   </refsect1>
 103
 104   <refsect1>
 105     <title>Notes</title>
 106
 107     <xi:include href="libelogind-pkgconfig.xml" xpointer="pkgconfig-text"/>
 108
 109     <para>Internally, this function parses the
 110     <varname>$WATCHDOG_PID</varname> and
 111     <varname>$WATCHDOG_USEC</varname> environment variable. The call
 112     will ignore these variables if <varname>$WATCHDOG_PID</varname>
 113     does not contain the PID of the current process, under the
 114     assumption that in that case, the variables were set for a
 115     different process further up the process tree.</para>
 116   </refsect1>
 117
 118   <refsect1>
 119     <title>Environment</title>
 120
 121     <variablelist class='environment-variables'>
 122       <varlistentry>
 123         <term><varname>$WATCHDOG_PID</varname></term>
 124
 125         <listitem><para>Set by the system manager for supervised
 126         process for which watchdog support is enabled, and contains
 127         the PID of that process. See above for
 128         details.</para></listitem>
 129       </varlistentry>
 130
 131       <varlistentry>
 132         <term><varname>$WATCHDOG_USEC</varname></term>
 133
 134         <listitem><para>Set by the system manager for supervised
 135         process for which watchdog support is enabled, and contains
 136         the watchdog timeout in µs. See above for
 137         details.</para></listitem>
 138       </varlistentry>
 139     </variablelist>
 140   </refsect1>
 141
 142   <refsect1>
 143     <title>See Also</title>
 144     <para>
 145       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 146       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 147       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 148       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 149       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 150       <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 151     </para>
 152   </refsect1>
 153
 154 </refentry>