man/sd_watchdog_enabled.xml

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