man/sd_watchdog_enabled.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="sd_watchdog_enabled"
   7   xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>sd_watchdog_enabled</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>sd_watchdog_enabled</refentrytitle>
  16     <manvolnum>3</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>sd_watchdog_enabled</refname>
  21     <refpurpose>Check whether the service manager expects watchdog keep-alive notifications from a service</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <funcsynopsis>
  26       <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  27
  28       <funcprototype>
  29         <funcdef>int <function>sd_watchdog_enabled</function></funcdef>
  30         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  31         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  32       </funcprototype>
  33     </funcsynopsis>
  34   </refsynopsisdiv>
  35
  36   <refsect1>
  37     <title>Description</title>
  38     <para><function>sd_watchdog_enabled()</function> may be called by
  39     a service to detect whether the service manager expects regular
  40     keep-alive watchdog notification events from it, and the timeout
  41     after which the manager will act on the service if it did not get
  42     such a notification.</para>
  43
  44     <para>If the <varname>$WATCHDOG_USEC</varname> environment
  45     variable is set, and the <varname>$WATCHDOG_PID</varname> variable
  46     is unset or set to the PID of the current process, the service
  47     manager expects notifications from this process. The manager will
  48     usually terminate a service when it does not get a notification
  49     message within the specified time after startup and after each
  50     previous message. It is recommended that a daemon sends a
  51     keep-alive notification message to the service manager every half
  52     of the time returned here. Notification messages may be sent with
  53     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  54     with a message string of <literal>WATCHDOG=1</literal>.</para>
  55
  56     <para>If the <parameter>unset_environment</parameter> parameter is
  57     non-zero, <function>sd_watchdog_enabled()</function> will unset
  58     the <varname>$WATCHDOG_USEC</varname> and
  59     <varname>$WATCHDOG_PID</varname> environment variables before
  60     returning (regardless of whether the function call itself
  61     succeeded or not). Those variables are no longer inherited by
  62     child processes. Further calls to
  63     <function>sd_watchdog_enabled()</function> will also return with
  64     zero.</para>
  65
  66     <para>If the <parameter>usec</parameter> parameter is non-<constant>NULL</constant>,
  67     <function>sd_watchdog_enabled()</function> will write the timeout
  68     in μs for the watchdog logic to it.</para>
  69
  70     <para>To enable service supervision with the watchdog logic, use
  71     <varname>WatchdogSec=</varname> in service files. See
  72     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  73     for details.</para>
  74
  75     <para>Use
  76     <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  77     to enable automatic watchdog support in
  78     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>-based event loops.</para>
  79   </refsect1>
  80
  81   <refsect1>
  82     <title>Return Value</title>
  83
  84     <para>On failure, this call returns a negative errno-style error
  85     code. If the service manager expects watchdog keep-alive
  86     notification messages to be sent, &gt; 0 is returned, otherwise 0
  87     is returned. Only if the return value is &gt; 0, the
  88     <parameter>usec</parameter> parameter is valid after the
  89     call.</para>
  90   </refsect1>
  91
  92   <refsect1>
  93     <title>Notes</title>
  94
  95     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
  96     <xi:include href="threads-aware.xml" xpointer="getenv"/>
  97
  98     <para>Internally, this function parses the
  99     <varname>$WATCHDOG_PID</varname> and
 100     <varname>$WATCHDOG_USEC</varname> environment variable. The call
 101     will ignore these variables if <varname>$WATCHDOG_PID</varname>
 102     does not contain the PID of the current process, under the
 103     assumption that in that case, the variables were set for a
 104     different process further up the process tree.</para>
 105   </refsect1>
 106
 107   <refsect1>
 108     <title>Environment</title>
 109
 110     <variablelist class='environment-variables'>
 111       <varlistentry>
 112         <term><varname>$WATCHDOG_PID</varname></term>
 113
 114         <listitem><para>Set by the system manager for supervised
 115         process for which watchdog support is enabled, and contains
 116         the PID of that process. See above for
 117         details.</para>
 118
 119         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 120       </varlistentry>
 121
 122       <varlistentry>
 123         <term><varname>$WATCHDOG_USEC</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 watchdog timeout in μs. See above for
 128         details.</para>
 129
 130         <xi:include href="version-info.xml" xpointer="v209"/></listitem>
 131       </varlistentry>
 132     </variablelist>
 133   </refsect1>
 134
 135   <refsect1>
 136     <title>History</title>
 137     <para><function>sd_watchdog_enabled()</function> was added in version 209.</para>
 138   </refsect1>
 139
 140   <refsect1>
 141     <title>See Also</title>
 142     <para>
 143       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 144       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 145       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 146       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 147       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 148       <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 149     </para>
 150   </refsect1>
 151
 152 </refentry>