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a354329f72
With this change it is possible to send file descriptors to PID 1, via sd_pid_notify_with_fds() which PID 1 will store individually for each service, and pass via the usual fd passing logic on next invocation. This is useful for enable daemon reload schemes where daemons serialize their state to /run, push their fds into PID 1 and terminate, restoring their state on next start from the data in /run and passed in from PID 1. The fds are kept by PID 1 as long as no POLLHUP or POLLERR is seen on them, and the service they belong to are either not dead or failed, or have a job queued.
429 lines
21 KiB
XML
429 lines
21 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 2010 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_notify"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_notify</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_notify</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_notify</refname>
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<refname>sd_notifyf</refname>
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<refname>sd_pid_notify</refname>
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<refname>sd_pid_notifyf</refname>
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<refname>sd_pid_notify_with_fds</refname>
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<refpurpose>Notify service manager about start-up completion and other service status changes</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_notify</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_notifyf</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>...</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notify</function></funcdef>
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<paramdef>pid_t <parameter>pid</parameter></paramdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notifyf</function></funcdef>
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<paramdef>pid_t <parameter>pid</parameter></paramdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>format</parameter></paramdef>
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<paramdef>...</paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
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<paramdef>pid_t <parameter>pid</parameter></paramdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>const char *<parameter>state</parameter></paramdef>
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<paramdef>const int *<parameter>fds</parameter></paramdef>
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<paramdef>unsigned <parameter>n_fds</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_notify()</function> may be called
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by a service to notify the service manager about
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state changes. It can be used to send arbitrary
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information, encoded in an environment-block-like
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string. Most importantly it can be used for start-up
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completion notification.</para>
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<para>If the <parameter>unset_environment</parameter>
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parameter is non-zero, <function>sd_notify()</function>
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will unset the <varname>$NOTIFY_SOCKET</varname>
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environment variable before returning (regardless of
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whether the function call itself succeeded or
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not). Further calls to
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<function>sd_notify()</function> will then fail, but
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the variable is no longer inherited by child
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processes.</para>
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<para>The <parameter>state</parameter> parameter
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should contain a newline-separated list of variable
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assignments, similar in style to an environment
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block. A trailing newline is implied if none is
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specified. The string may contain any kind of variable
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assignments, but the following shall be considered
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well-known:</para>
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<variablelist>
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<varlistentry>
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<term>READY=1</term>
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<listitem><para>Tells the service
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manager that service startup is
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finished. This is only used by systemd
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if the service definition file has
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Type=notify set. Since there is little
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value in signaling non-readiness, the
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only value services should send is
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<literal>READY=1</literal>
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(i.e. <literal>READY=0</literal> is
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not defined).</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>RELOADING=1</term>
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<listitem><para>Tells the service manager
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that the service is reloading its
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configuration. This is useful to allow
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the service manager to track the service's
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internal state, and present it to the
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user. Note that a service that sends
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this notification must also send a
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<literal>READY=1</literal>
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notification when it completed
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reloading its
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configuration.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>STOPPING=1</term>
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<listitem><para>Tells the service manager
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that the service is beginning its
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shutdown. This is useful to allow the
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service manager to track the service's
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internal state, and present it to the
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user.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>STATUS=...</term>
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<listitem><para>Passes a single-line
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UTF-8 status string back to the service manager
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that describes the service state. This
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is free-form and can be used for
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various purposes: general state
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feedback, fsck-like programs could
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pass completion percentages and
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failing programs could pass a human
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readable error message. Example:
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<literal>STATUS=Completed 66% of file
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system
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check...</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>ERRNO=...</term>
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<listitem><para>If a service fails, the
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errno-style error code, formatted as
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string. Example: <literal>ERRNO=2</literal> for
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ENOENT.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>BUSERROR=...</term>
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<listitem><para>If a service fails, the
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D-Bus error-style error code. Example:
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<literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>MAINPID=...</term>
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<listitem><para>The main process ID (PID) of the
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service, in case the service manager did
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not fork off the process
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itself. Example:
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<literal>MAINPID=4711</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG=1</term>
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<listitem><para>Tells the service manager to
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update the watchdog timestamp. This is
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the keep-alive ping that services need
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to issue in regular intervals if
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<varname>WatchdogSec=</varname> is
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enabled for it. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for information how to enable this
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functionality and
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<citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for the details of how the service can
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check if the the watchdog is enabled.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDSTORE=1</term>
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<listitem><para>Stores additional file
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descriptors in the service
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manager. File descriptors sent this
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way will be maintained per-service by
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the service manager and be passed
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again using the usual file descriptor
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passing logic on the next invocation
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of the service (see
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<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>). This
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is useful for implementing service
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restart schemes where services
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serialize their state to
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<filename>/run</filename>, push their
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file descriptors to the system
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manager, and are then restarted,
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retrieving their state again via
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socket passing and
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<filename>/run</filename>. Note that
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the service manager will accept
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messages for a service only if
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<varname>FileDescriptorStoreMax=</varname>
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is set to non-zero for it (defaults to
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zero). See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details. Multiple arrays of file
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descriptors may be sent in seperate
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messages, in which case the arrays are
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combined. Note that the service
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manager removes duplicate file
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descriptors before passing them to the
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service. Use
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<function>sd_pid_notify_with_fds()</function>
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to send messages with
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<literal>FDSTORE=1</literal>, see
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below.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>It is recommended to prefix variable names that
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are not listed above with <varname>X_</varname> to
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avoid namespace clashes.</para>
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<para>Note that systemd will accept status data sent
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from a service only if the
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<varname>NotifyAccess=</varname> option is correctly
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set in the service definition file. 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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<para><function>sd_notifyf()</function> is similar to
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<function>sd_notify()</function> but takes a
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<function>printf()</function>-like format string plus
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arguments.</para>
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<para><function>sd_pid_notify()</function> and
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<function>sd_pid_notifyf()</function> are similar to
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<function>sd_notify()</function> and
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<function>sd_notifyf()</function> but take a process
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ID (PID) to use as originating PID for the message as
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first argument. This is useful to send notification
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messages on behalf of other processes, provided the
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appropriate privileges are available. If the PID
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argument is specified as 0 the process ID of the
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calling process is used, in which case the calls are
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fully equivalent to <function>sd_notify()</function>
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and <function>sd_notifyf()</function>.</para>
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<para><function>sd_pid_notify_with_fds()</function> is
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similar to <function>sd_pid_notify()</function> but
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takes an additional array of file descriptors. These
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file descriptors are sent along the notification
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message to the service manager. This is particularly
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useful for sending <literal>FDSTORE=1</literal>
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messages, as described above. The additional arguments
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are a pointer to the file descriptor array plus the
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number of file descriptors in the array. If the number
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of file descriptors is passed as 0, the call is fully
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equivalent to <function>sd_pid_notify()</function>,
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i.e. no file descriptors are passed. Note that sending
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file descriptors to the service manager on messages
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that do not expect them (i.e. without
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<literal>FDSTORE=1</literal>) they are immediately
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closed on reception.</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, these calls return a negative
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errno-style error code. If
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<varname>$NOTIFY_SOCKET</varname> was not set and
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hence no status data could be sent, 0 is returned. If
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the status was sent, these functions return with a
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positive return value. In order to support both, init
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systems that implement this scheme and those which
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do not, it is generally recommended to ignore the return
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value of this 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, these functions send a single
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datagram with the state string as payload to the
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<constant>AF_UNIX</constant> socket referenced in the
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<varname>$NOTIFY_SOCKET</varname> environment
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variable. If the first character of
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<varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
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understood as Linux abstract namespace socket. The
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datagram is accompanied by the process credentials of
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the sending service, using SCM_CREDENTIALS.</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>$NOTIFY_SOCKET</varname></term>
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<listitem><para>Set by the service manager
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for supervised processes for status
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and start-up completion
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notification. This environment variable
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specifies the socket
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<function>sd_notify()</function> talks
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to. See above for 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>Examples</title>
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<example>
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<title>Start-up Notification</title>
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<para>When a service finished starting up, it
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might issue the following call to notify
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the service manager:</para>
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<programlisting>sd_notify(0, "READY=1");</programlisting>
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</example>
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<example>
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<title>Extended Start-up Notification</title>
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<para>A service could send the following after
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completing initialization:</para>
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<programlisting>sd_notifyf(0, "READY=1\n"
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"STATUS=Processing requests...\n"
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"MAINPID=%lu",
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(unsigned long) getpid());</programlisting>
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</example>
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<example>
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<title>Error Cause Notification</title>
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<para>A service could send the following shortly before exiting, on failure:</para>
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<programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
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"ERRNO=%i",
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strerror(errno),
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errno);</programlisting>
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</example>
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<example>
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<title>Store a File Descriptor in the Service Manager</title>
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<para>To store an open file descriptor in the
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service manager, in order to continue
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operation after a service restart without
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losing state use
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<literal>FDSTORE=1</literal>:</para>
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<programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1", &fd, 1);</programlisting>
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</example>
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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_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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