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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+ This file is part of systemd.
+
+ Copyright 2013 Lennart Poettering
+
+ systemd is free software; you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published by
+ the Free Software Foundation; either version 2.1 of the License, or
+ (at your option) any later version.
+
+ systemd is distributed in the hope that it will be useful, but
+ WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public License
+ along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="sd_watchdog_enabled">
+
+ <refentryinfo>
+ <title>sd_watchdog_enabled</title>
+ <productname>systemd</productname>
+
+ <authorgroup>
+ <author>
+ <contrib>Developer</contrib>
+ <firstname>Lennart</firstname>
+ <surname>Poettering</surname>
+ <email>lennart@poettering.net</email>
+ </author>
+ </authorgroup>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_watchdog_enabled</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_watchdog_enabled</refname>
+ <refpurpose>Check whether the service manager expects watchdog keep-alive notifications from a service</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_watchdog_enabled</function></funcdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>const uint64_t *<parameter>usec</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+ <para><function>sd_watchdog_enabled()</function> may
+ be called by a service to detect whether the service
+ manager expects regular keep-alive watchdog
+ notification events from it, and the timeout after
+ which the manager will act on the service if it did
+ not get such a notification.</para>
+
+ <para>If the <parameter>unset_environment</parameter>
+ parameter is non-zero,
+ <function>sd_watchdog_enabled()</function> will unset
+ the <varname>$WATCHDOG_USEC</varname> and
+ <varname>$WATCHDOG_PID</varname> environment variables
+ before returning (regardless whether the function call
+ itself succeeded or not). Further calls to
+ <function>sd_watchdog_enabled()</function> will then
+ return with zero, but the variable is no longer
+ inherited by child processes.</para>
+
+ <para>If the <parameter>usec</parameter> parameter is
+ non-NULL <function>sd_watchdog_enabled()</function>
+ will return the timeout in µs for the watchdog
+ logic. The service manager will usually terminate a
+ service when it did not get a notification message
+ within the specified time after startup and after each
+ previous message. It is recommended that a daemon
+ sends a keep-alive notification message to the service
+ manager every half of the time returned
+ here. Notification messages may be sent with
+ <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ with a message string of
+ <literal>WATCHDOG=1</literal>.</para>
+
+ <para>To enable service supervision with the watchdog
+ logic use <varname>WatchdogSec=</varname> in service
+ files. See
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Return Value</title>
+
+ <para>On failure, this call returns a negative
+ errno-style error code. If the service manager expects
+ watchdog keep-alive notification messages to be sent,
+ > 0 is returned, otherwise 0 is returned. Only if
+ the return value is > 0 the
+ <parameter>usec</parameter> parameter is valid after
+ the call.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>This function is provided by the reference
+ implementation of APIs for new-style daemons and
+ distributed with the systemd package. The algorithm
+ it implements is simple, and can easily be
+ reimplemented in daemons if it is important to support
+ this interface without using the reference
+ implementation.</para>
+
+ <para>Internally, this functions parses the
+ <varname>$WATCHDOG_PID</varname> and
+ <varname>$WATCHDOG_USEC</varname> environment
+ variable. The call will ignore these variables if
+ <varname>$WATCHDOG_PID</varname> does containe the PID
+ of the current process, under the assumption that in
+ that case the variables were set for a different
+ process further up the process tree.</para>
+
+ <para>For details about the algorithm check the
+ liberally licensed reference implementation sources:
+ <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
+ and <ulink
+ url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
+
+ <para><function>sd_watchdog_enabled()</function> is
+ implemented in the reference implementation's
+ <filename>sd-daemon.c</filename> and
+ <filename>sd-daemon.h</filename> files. These
+ interfaces are available as shared library, which can
+ be compiled and linked to with the
+ <constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ file. Alternatively, applications consuming these APIs
+ may copy the implementation into their source
+ tree. For more details about the reference
+ implementation see
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
+
+ <para>If the reference implementation is used as
+ drop-in files and -DDISABLE_SYSTEMD is set during
+ compilation, these functions will always return 0 and
+ otherwise become a NOP.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Environment</title>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$WATCHDOG_PID</varname></term>
+
+ <listitem><para>Set by the system
+ manager for supervised process for
+ which watchdog support is enabled, and
+ contains the PID of that process. See
+ above for details.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>$WATCHDOG_USEC</varname></term>
+
+ <listitem><para>Set by the system
+ manager for supervised process for
+ which watchdog support is enabled, and
+ contains the watchdog timeout in µs
+ See above for
+ details.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>
~ianmdlvl / elogind.git / blobdiff