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176 lines
6.6 KiB
XML
176 lines
6.6 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2013 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_watchdog_enabled"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_watchdog_enabled</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_watchdog_enabled</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_watchdog_enabled</refname>
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<refpurpose>Check whether the service manager expects watchdog keep-alive notifications from a service</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-daemon.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_watchdog_enabled</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>uint64_t *<parameter>usec</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_watchdog_enabled()</function> may be called by
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a service to detect whether the service manager expects regular
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keep-alive watchdog notification events from it, and the timeout
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after which the manager will act on the service if it did not get
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such a notification.</para>
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<para>If the <varname>$WATCHDOG_USEC</varname> environment
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variable is set, and the <varname>$WATCHDOG_PID</varname> variable
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is unset or set to the PID of the current process, the service
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manager expects notifications from this process. The manager will
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usually terminate a service when it does not get a notification
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message within the specified time after startup and after each
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previous message. It is recommended that a daemon sends a
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keep-alive notification message to the service manager every half
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of the time returned here. Notification messages may be sent with
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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with a message string of <literal>WATCHDOG=1</literal>.</para>
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<para>If the <parameter>unset_environment</parameter> parameter is
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non-zero, <function>sd_watchdog_enabled()</function> will unset
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the <varname>$WATCHDOG_USEC</varname> and
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<varname>$WATCHDOG_PID</varname> environment variables before
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returning (regardless of whether the function call itself
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succeeded or not). Those variables are no longer inherited by
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child processes. Further calls to
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<function>sd_watchdog_enabled()</function> will also return with
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zero.</para>
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<para>If the <parameter>usec</parameter> parameter is non-NULL,
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<function>sd_watchdog_enabled()</function> will write the timeout
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in µs for the watchdog logic to it.</para>
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<para>To enable service supervision with the watchdog logic, use
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<varname>WatchdogSec=</varname> in service files. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para>On failure, this call returns a negative errno-style error
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code. If the service manager expects watchdog keep-alive
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notification messages to be sent, > 0 is returned, otherwise 0
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is returned. Only if the return value is > 0, the
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<parameter>usec</parameter> parameter is valid after the
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call.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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<para>Internally, this functions parses the
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<varname>$WATCHDOG_PID</varname> and
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<varname>$WATCHDOG_USEC</varname> environment variable. The call
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will ignore these variables if <varname>$WATCHDOG_PID</varname>
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does not contain the PID of the current process, under the
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assumption that in that case, the variables were set for a
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different process further up the process tree.</para>
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</refsect1>
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<refsect1>
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<title>Environment</title>
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<variablelist class='environment-variables'>
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<varlistentry>
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<term><varname>$WATCHDOG_PID</varname></term>
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<listitem><para>Set by the system manager for supervised
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process for which watchdog support is enabled, and contains
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the PID of that process. See above for
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details.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>$WATCHDOG_USEC</varname></term>
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<listitem><para>Set by the system manager for supervised
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process for which watchdog support is enabled, and contains
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the watchdog timeout in µs See above for
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details.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>History</title>
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<para>The watchdog functionality and the
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<varname>$WATCHDOG_USEC</varname> variable were added in
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systemd-41.</para>
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<para><function>sd_watchdog_enabled()</function> function was
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added in systemd-209. Since that version the
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<varname>$WATCHDOG_PID</varname> variable is also set.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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