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514094f9 | 1 | <?xml version='1.0'?> |
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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 | <!-- | |
572eb058 | 6 | SPDX-License-Identifier: LGPL-2.1+ |
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7 | --> |
8 | ||
9 | <refentry id="sd_event_set_watchdog" xmlns:xi="http://www.w3.org/2001/XInclude"> | |
10 | ||
11 | <refentryinfo> | |
12 | <title>sd_event_set_watchdog</title> | |
13 | <productname>systemd</productname> | |
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14 | </refentryinfo> |
15 | ||
16 | <refmeta> | |
17 | <refentrytitle>sd_event_set_watchdog</refentrytitle> | |
18 | <manvolnum>3</manvolnum> | |
19 | </refmeta> | |
20 | ||
21 | <refnamediv> | |
22 | <refname>sd_event_set_watchdog</refname> | |
23 | <refname>sd_event_get_watchdog</refname> | |
24 | ||
25 | <refpurpose>Enable event loop watchdog support</refpurpose> | |
26 | </refnamediv> | |
27 | ||
28 | <refsynopsisdiv> | |
29 | <funcsynopsis> | |
30 | <funcsynopsisinfo>#include <systemd/sd-event.h></funcsynopsisinfo> | |
31 | ||
32 | <funcprototype> | |
33 | <funcdef>int <function>sd_event_set_watchdog</function></funcdef> | |
34 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
35 | <paramdef>int b</paramdef> | |
36 | </funcprototype> | |
37 | ||
38 | <funcprototype> | |
39 | <funcdef>int <function>sd_event_get_watchdog</function></funcdef> | |
40 | <paramdef>sd_event *<parameter>event</parameter></paramdef> | |
41 | </funcprototype> | |
42 | ||
43 | </funcsynopsis> | |
44 | </refsynopsisdiv> | |
45 | ||
46 | <refsect1> | |
47 | <title>Description</title> | |
48 | ||
49 | <para><function>sd_event_set_watchdog()</function> may be used to | |
50 | enable or disable automatic watchdog notification support in the | |
51 | event loop object specified in the <parameter>event</parameter> | |
52 | parameter. Specifically, depending on the <parameter>b</parameter> | |
53 | boolean argument this will make sure the event loop wakes up in | |
54 | regular intervals and sends watchdog notification messages to the | |
55 | service manager, if this was requested by the service | |
56 | manager. Watchdog support is determined with | |
57 | <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
58 | and watchdog messages are sent with | |
59 | <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>. See | |
60 | the <varname>WatchdogSec=</varname> setting in | |
61 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
62 | for details on how to enable watchdog support for a service and | |
63 | the protocol used. The wake-up interval is chosen as half the | |
64 | watchdog timeout declared by the service manager via the | |
65 | <varname>$WATCHDOG_USEC</varname> environment variable. If the | |
66 | service manager did not request watchdog notifications, or if the | |
67 | process was not invoked by the service manager this call with a | |
68 | true <parameter>b</parameter> parameter executes no | |
69 | operation. Passing a false <parameter>b</parameter> parameter will | |
70 | disable the automatic sending of watchdog notification messages if | |
71 | it was enabled before. Newly allocated event loop objects have | |
72 | this feature disabled.</para> | |
73 | ||
74 | <para>The first watchdog notification message is sent immediately | |
75 | when <function>set_event_set_watchdog()</function> is invoked with | |
76 | a true <parameter>b</parameter> parameter.</para> | |
77 | ||
78 | <para>The watchdog logic is designed to allow the service manager | |
79 | to automatically detect services that ceased processing of | |
80 | incoming events, and thus appear "hung". Watchdog notifications | |
81 | are sent out only at the beginning of each event loop | |
82 | iteration. If an event source dispatch function blocks for an | |
83 | excessively long time and does not return execution to the event | |
84 | loop quickly, this might hence cause the notification message to | |
85 | be delayed, and possibly result in abnormal program termination, | |
86 | as configured in the service unit file.</para> | |
87 | ||
88 | <para><function>sd_event_get_watchdog()</function> may be used to | |
89 | determine whether watchdog support was previously requested by a | |
90 | call to <function>sd_event_set_watchdog()</function> with a true | |
91 | <parameter>b</parameter> parameter and successfully | |
92 | enabled.</para> | |
93 | </refsect1> | |
94 | ||
95 | <refsect1> | |
96 | <title>Return Value</title> | |
97 | ||
98 | <para>On success, <function>sd_event_set_watchdog()</function> and | |
99 | <function>sd_event_get_watchdog()</function> return a non-zero | |
100 | positive integer if the service manager requested watchdog support | |
101 | and watchdog support was successfully enabled. They return zero if | |
102 | the service manager did not request watchdog support, or if | |
103 | watchdog support was explicitly disabled with a false | |
104 | <parameter>b</parameter> parameter. On failure, they return a | |
105 | negative errno-style error | |
106 | code.</para> | |
107 | </refsect1> | |
108 | ||
109 | <refsect1> | |
110 | <title>Errors</title> | |
111 | ||
112 | <para>Returned errors may indicate the following problems:</para> | |
113 | ||
114 | <variablelist> | |
115 | ||
116 | <varlistentry> | |
117 | <term><constant>-ECHILD</constant></term> | |
118 | ||
119 | <listitem><para>The event loop has been created in a different process.</para></listitem> | |
120 | </varlistentry> | |
121 | ||
122 | <varlistentry> | |
123 | <term><constant>-EINVAL</constant></term> | |
124 | ||
125 | <listitem><para>The passed event loop object was invalid.</para></listitem> | |
126 | </varlistentry> | |
127 | ||
128 | </variablelist> | |
129 | </refsect1> | |
130 | ||
131 | <xi:include href="libsystemd-pkgconfig.xml" /> | |
132 | ||
133 | <refsect1> | |
134 | <title>See Also</title> | |
135 | ||
136 | <para> | |
137 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
138 | <citerefentry><refentrytitle>sd-event</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
139 | <citerefentry><refentrytitle>sd_event_new</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
140 | <citerefentry><refentrytitle>sd_event_add_io</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
141 | <citerefentry><refentrytitle>sd_event_add_time</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
142 | <citerefentry><refentrytitle>sd_event_add_signal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
143 | <citerefentry><refentrytitle>sd_event_add_child</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
8274a30d | 144 | <citerefentry><refentrytitle>sd_event_add_inotify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
dc83f27a | 145 | <citerefentry><refentrytitle>sd_event_add_defer</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
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146 | <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
147 | <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
148 | <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> | |
149 | </para> | |
150 | </refsect1> | |
151 | ||
152 | </refentry> |