199 lines
9.4 KiB
XML
199 lines
9.4 KiB
XML
<?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 of 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>$WATCHDOG_PID</varname> does containe the PID
|
||
of the current process, under the assumption that in
|
||
that case the variables were set for a different
|
||
process further up the process tree.</para>
|
||
|
||
<para>For details about the algorithm check the
|
||
liberally licensed reference implementation sources:
|
||
<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
|
||
and <ulink
|
||
url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
|
||
|
||
<para><function>sd_watchdog_enabled()</function> is
|
||
implemented in the reference implementation's
|
||
<filename>sd-daemon.c</filename> and
|
||
<filename>sd-daemon.h</filename> files. These
|
||
interfaces are available as a shared library, which can
|
||
be compiled and linked to with the
|
||
<constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
|
||
file. Alternatively, applications consuming these APIs
|
||
may copy the implementation into their source
|
||
tree. For more details about the reference
|
||
implementation see
|
||
<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
|
||
|
||
<para>If the reference implementation is used as
|
||
drop-in files and -DDISABLE_SYSTEMD is set during
|
||
compilation, these functions will always return 0 and
|
||
otherwise become a NOP.</para>
|
||
</refsect1>
|
||
|
||
<refsect1>
|
||
<title>Environment</title>
|
||
|
||
<variablelist class='environment-variables'>
|
||
<varlistentry>
|
||
<term><varname>$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>
|