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199 lines
9.4 KiB
XML
199 lines
9.4 KiB
XML
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<?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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<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>const 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
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be called by a service to detect whether the service
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manager expects regular keep-alive watchdog
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notification events from it, and the timeout after
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which the manager will act on the service if it did
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not get such a notification.</para>
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<para>If the <parameter>unset_environment</parameter>
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parameter is non-zero,
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<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
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before returning (regardless whether the function call
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itself succeeded or not). Further calls to
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<function>sd_watchdog_enabled()</function> will then
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return with zero, but the variable is no longer
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inherited by child processes.</para>
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<para>If the <parameter>usec</parameter> parameter is
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non-NULL <function>sd_watchdog_enabled()</function>
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will return the timeout in µs for the watchdog
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logic. The service manager will usually terminate a
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service when it did not get a notification message
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within the specified time after startup and after each
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previous message. It is recommended that a daemon
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sends a keep-alive notification message to the service
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manager every half of the time returned
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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
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<literal>WATCHDOG=1</literal>.</para>
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<para>To enable service supervision with the watchdog
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logic use <varname>WatchdogSec=</varname> in service
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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
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errno-style error code. If the service manager expects
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watchdog keep-alive notification messages to be sent,
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> 0 is returned, otherwise 0 is returned. Only if
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the return value is > 0 the
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<parameter>usec</parameter> parameter is valid after
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the call.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>This function is provided by the reference
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implementation of APIs for new-style daemons and
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distributed with the systemd package. The algorithm
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it implements is simple, and can easily be
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reimplemented in daemons if it is important to support
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this interface without using the reference
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implementation.</para>
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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
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variable. The call will ignore these variables if
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<varname>$WATCHDOG_PID</varname> does containe the PID
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of the current process, under the assumption that in
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that case the variables were set for a different
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process further up the process tree.</para>
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<para>For details about the algorithm check the
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liberally licensed reference implementation sources:
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<ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
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and <ulink
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url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
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<para><function>sd_watchdog_enabled()</function> is
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implemented in the reference implementation's
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<filename>sd-daemon.c</filename> and
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<filename>sd-daemon.h</filename> files. These
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interfaces are available as shared library, which can
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be compiled and linked to with the
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<constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file. Alternatively, applications consuming these APIs
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may copy the implementation into their source
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tree. For more details about the reference
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implementation see
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<citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
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<para>If the reference implementation is used as
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drop-in files and -DDISABLE_SYSTEMD is set during
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compilation, these functions will always return 0 and
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otherwise become a NOP.</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
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manager for supervised process for
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which watchdog support is enabled, and
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contains the PID of that process. See
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above for 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
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manager for supervised process for
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which watchdog support is enabled, and
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contains the watchdog timeout in µs
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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>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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