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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>
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