man/sd_watchdog_enabled.xml

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   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   This file is part of systemd.
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  10   Copyright 2013 Lennart Poettering
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  12
  13 <refentry id="sd_watchdog_enabled"
  14   xmlns:xi="http://www.w3.org/2001/XInclude">
  15
  16   <refentryinfo>
  17     <title>sd_watchdog_enabled</title>
  18     <productname>systemd</productname>
  19
  20     <authorgroup>
  21       <author>
  22         <contrib>Developer</contrib>
  23         <firstname>Lennart</firstname>
  24         <surname>Poettering</surname>
  25         <email>lennart@poettering.net</email>
  26       </author>
  27     </authorgroup>
  28   </refentryinfo>
  29
  30   <refmeta>
  31     <refentrytitle>sd_watchdog_enabled</refentrytitle>
  32     <manvolnum>3</manvolnum>
  33   </refmeta>
  34
  35   <refnamediv>
  36     <refname>sd_watchdog_enabled</refname>
  37     <refpurpose>Check whether the service manager expects watchdog keep-alive notifications from a service</refpurpose>
  38   </refnamediv>
  39
  40   <refsynopsisdiv>
  41     <funcsynopsis>
  42       <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  43
  44       <funcprototype>
  45         <funcdef>int <function>sd_watchdog_enabled</function></funcdef>
  46         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  47         <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
  48       </funcprototype>
  49     </funcsynopsis>
  50   </refsynopsisdiv>
  51
  52   <refsect1>
  53     <title>Description</title>
  54     <para><function>sd_watchdog_enabled()</function> may be called by
  55     a service to detect whether the service manager expects regular
  56     keep-alive watchdog notification events from it, and the timeout
  57     after which the manager will act on the service if it did not get
  58     such a notification.</para>
  59
  60     <para>If the <varname>$WATCHDOG_USEC</varname> environment
  61     variable is set, and the <varname>$WATCHDOG_PID</varname> variable
  62     is unset or set to the PID of the current process, the service
  63     manager expects notifications from this process. The manager will
  64     usually terminate a service when it does not get a notification
  65     message within the specified time after startup and after each
  66     previous message. It is recommended that a daemon sends a
  67     keep-alive notification message to the service manager every half
  68     of the time returned here. Notification messages may be sent with
  69     <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  70     with a message string of <literal>WATCHDOG=1</literal>.</para>
  71
  72     <para>If the <parameter>unset_environment</parameter> parameter is
  73     non-zero, <function>sd_watchdog_enabled()</function> will unset
  74     the <varname>$WATCHDOG_USEC</varname> and
  75     <varname>$WATCHDOG_PID</varname> environment variables before
  76     returning (regardless of whether the function call itself
  77     succeeded or not). Those variables are no longer inherited by
  78     child processes. Further calls to
  79     <function>sd_watchdog_enabled()</function> will also return with
  80     zero.</para>
  81
  82     <para>If the <parameter>usec</parameter> parameter is non-NULL,
  83     <function>sd_watchdog_enabled()</function> will write the timeout
  84     in µs for the watchdog logic to it.</para>
  85
  86     <para>To enable service supervision with the watchdog logic, use
  87     <varname>WatchdogSec=</varname> in service files. See
  88     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  89     for details.</para>
  90
  91     <para>Use
  92     <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
  93     to enable automatic watchdog support in
  94     <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>-based event loops.</para>
  95   </refsect1>
  96
  97   <refsect1>
  98     <title>Return Value</title>
  99
 100     <para>On failure, this call returns a negative errno-style error
 101     code. If the service manager expects watchdog keep-alive
 102     notification messages to be sent, &gt; 0 is returned, otherwise 0
 103     is returned. Only if the return value is &gt; 0, the
 104     <parameter>usec</parameter> parameter is valid after the
 105     call.</para>
 106   </refsect1>
 107
 108   <refsect1>
 109     <title>Notes</title>
 110
 111     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 112
 113     <para>Internally, this function parses the
 114     <varname>$WATCHDOG_PID</varname> and
 115     <varname>$WATCHDOG_USEC</varname> environment variable. The call
 116     will ignore these variables if <varname>$WATCHDOG_PID</varname>
 117     does not contain the PID of the current process, under the
 118     assumption that in that case, the variables were set for a
 119     different process further up the process tree.</para>
 120   </refsect1>
 121
 122   <refsect1>
 123     <title>Environment</title>
 124
 125     <variablelist class='environment-variables'>
 126       <varlistentry>
 127         <term><varname>$WATCHDOG_PID</varname></term>
 128
 129         <listitem><para>Set by the system manager for supervised
 130         process for which watchdog support is enabled, and contains
 131         the PID of that process. See above for
 132         details.</para></listitem>
 133       </varlistentry>
 134
 135       <varlistentry>
 136         <term><varname>$WATCHDOG_USEC</varname></term>
 137
 138         <listitem><para>Set by the system manager for supervised
 139         process for which watchdog support is enabled, and contains
 140         the watchdog timeout in µs. See above for
 141         details.</para></listitem>
 142       </varlistentry>
 143     </variablelist>
 144   </refsect1>
 145
 146   <refsect1>
 147     <title>See Also</title>
 148     <para>
 149       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 150       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 151       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 152       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 153       <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 154       <citerefentry><refentrytitle>sd_event_set_watchdog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 155     </para>
 156   </refsect1>
 157
 158 </refentry>