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+<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
+<!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 2010 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_notify"
+  xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>sd_notify</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_notify</refentrytitle>
+    <manvolnum>3</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>sd_notify</refname>
+    <refname>sd_notifyf</refname>
+    <refname>sd_pid_notify</refname>
+    <refname>sd_pid_notifyf</refname>
+    <refname>sd_pid_notify_with_fds</refname>
+    <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <funcsynopsis>
+      <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
+
+      <funcprototype>
+        <funcdef>int <function>sd_notify</function></funcdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>state</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_notifyf</function></funcdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>...</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_notify</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>state</parameter></paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_notifyf</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>format</parameter></paramdef>
+        <paramdef>...</paramdef>
+      </funcprototype>
+
+      <funcprototype>
+        <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
+        <paramdef>pid_t <parameter>pid</parameter></paramdef>
+        <paramdef>int <parameter>unset_environment</parameter></paramdef>
+        <paramdef>const char *<parameter>state</parameter></paramdef>
+        <paramdef>const int *<parameter>fds</parameter></paramdef>
+        <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
+      </funcprototype>
+    </funcsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+    <para><function>sd_notify()</function> may be called by a service
+    to notify the service manager about state changes. It can be used
+    to send arbitrary information, encoded in an
+    environment-block-like string. Most importantly, it can be used for
+    start-up completion notification.</para>
+
+    <para>If the <parameter>unset_environment</parameter> parameter is
+    non-zero, <function>sd_notify()</function> will unset the
+    <varname>$NOTIFY_SOCKET</varname> environment variable before
+    returning (regardless of whether the function call itself
+    succeeded or not). Further calls to
+    <function>sd_notify()</function> will then fail, but the variable
+    is no longer inherited by child processes.</para>
+
+    <para>The <parameter>state</parameter> parameter should contain a
+    newline-separated list of variable assignments, similar in style
+    to an environment block. A trailing newline is implied if none is
+    specified. The string may contain any kind of variable
+    assignments, but the following shall be considered
+    well-known:</para>
+
+    <variablelist>
+      <varlistentry>
+        <term>READY=1</term>
+
+        <listitem><para>Tells the service manager that service startup
+        is finished. This is only used by systemd if the service
+        definition file has Type=notify set. Since there is little
+        value in signaling non-readiness, the only value services
+        should send is <literal>READY=1</literal> (i.e.
+        <literal>READY=0</literal> is not defined).</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>RELOADING=1</term>
+
+        <listitem><para>Tells the service manager that the service is
+        reloading its configuration. This is useful to allow the
+        service manager to track the service's internal state, and
+        present it to the user. Note that a service that sends this
+        notification must also send a <literal>READY=1</literal>
+        notification when it completed reloading its
+        configuration.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>STOPPING=1</term>
+
+        <listitem><para>Tells the service manager that the service is
+        beginning its shutdown. This is useful to allow the service
+        manager to track the service's internal state, and present it
+        to the user.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>STATUS=...</term>
+
+        <listitem><para>Passes a single-line UTF-8 status string back
+        to the service manager that describes the service state. This
+        is free-form and can be used for various purposes: general
+        state feedback, fsck-like programs could pass completion
+        percentages and failing programs could pass a human-readable
+        error message. Example: <literal>STATUS=Completed 66% of file
+        system check...</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>ERRNO=...</term>
+
+        <listitem><para>If a service fails, the errno-style error
+        code, formatted as string. Example: <literal>ERRNO=2</literal>
+        for ENOENT.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>BUSERROR=...</term>
+
+        <listitem><para>If a service fails, the D-Bus error-style
+        error code. Example:
+        <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>MAINPID=...</term>
+
+        <listitem><para>The main process ID (PID) of the service, in
+        case the service manager did not fork off the process itself.
+        Example: <literal>MAINPID=4711</literal></para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>WATCHDOG=1</term>
+
+        <listitem><para>Tells the service manager to update the
+        watchdog timestamp. This is the keep-alive ping that services
+        need to issue in regular intervals if
+        <varname>WatchdogSec=</varname> is enabled for it. See
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        for information how to enable this functionality and
+        <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+        for the details of how the service can check whether the
+        watchdog is enabled. </para></listitem>
+      </varlistentry>
+
+
+      <varlistentry>
+        <term>FDSTORE=1</term>
+
+        <listitem><para>Stores additional file descriptors in the service manager. File
+        descriptors sent this way will be maintained per-service by the service manager
+        and will be passed again using the usual file descriptor passing logic on the next
+        invocation of the service, see
+        <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
+        This is useful for implementing service restart schemes where services serialize
+        their state to <filename>/run</filename>, push their file descriptors to the
+        system manager, and are then restarted, retrieving their state again via socket
+        passing and <filename>/run</filename>. Note that the service manager will accept
+        messages for a service only if <varname>FileDescriptorStoreMax=</varname> is set
+        to non-zero for it (defaults to zero, see
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
+        File descriptors must be pollable, see
+        <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
+        Multiple arrays of file descriptors may be sent in separate messages, in which
+        case the arrays are combined.  Note that the service manager removes duplicate
+        file descriptors before passing them to the service. Use
+        <function>sd_pid_notify_with_fds()</function> to send messages with
+        <literal>FDSTORE=1</literal>, see below.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>FDNAME=...</term>
+
+        <listitem><para>When used in combination with
+        <varname>FDSTORE=1</varname>, specifies a name for the
+        submitted file descriptors. This name is passed to the service
+        during activation, and may be queried using
+        <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
+        descriptors submitted without this field set, will implicitly
+        get the name <literal>stored</literal> assigned. Note that, if
+        multiple file descriptors are submitted at once, the specified
+        name will be assigned to all of them. In order to assign
+        different names to submitted file descriptors, submit them in
+        separate invocations of
+        <function>sd_pid_notify_with_fds()</function>. The name may
+        consist of any ASCII character, but must not contain control
+        characters or <literal>:</literal>. It may not be longer than
+        255 characters. If a submitted name does not follow these
+        restrictions, it is ignored.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term>WATCHDOG_USEC=...</term>
+
+        <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
+        Notice that this is not available when using <function>sd_event_set_watchdog()</function>
+        or <function>sd_watchdog_enabled()</function>.
+        Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
+      </varlistentry>
+
+    </variablelist>
+
+    <para>It is recommended to prefix variable names that are not
+    listed above with <varname>X_</varname> to avoid namespace
+    clashes.</para>
+
+    <para>Note that systemd will accept status data sent from a
+    service only if the <varname>NotifyAccess=</varname> option is
+    correctly set in the service definition file. See
+    <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for details.</para>
+
+    <para><function>sd_notifyf()</function> is similar to
+    <function>sd_notify()</function> but takes a
+    <function>printf()</function>-like format string plus
+    arguments.</para>
+
+    <para><function>sd_pid_notify()</function> and
+    <function>sd_pid_notifyf()</function> are similar to
+    <function>sd_notify()</function> and
+    <function>sd_notifyf()</function> but take a process ID (PID) to
+    use as originating PID for the message as first argument. This is
+    useful to send notification messages on behalf of other processes,
+    provided the appropriate privileges are available. If the PID
+    argument is specified as 0, the process ID of the calling process
+    is used, in which case the calls are fully equivalent to
+    <function>sd_notify()</function> and
+    <function>sd_notifyf()</function>.</para>
+
+    <para><function>sd_pid_notify_with_fds()</function> is similar to
+    <function>sd_pid_notify()</function> but takes an additional array
+    of file descriptors. These file descriptors are sent along the
+    notification message to the service manager. This is particularly
+    useful for sending <literal>FDSTORE=1</literal> messages, as
+    described above. The additional arguments are a pointer to the
+    file descriptor array plus the number of file descriptors in the
+    array. If the number of file descriptors is passed as 0, the call
+    is fully equivalent to <function>sd_pid_notify()</function>, i.e.
+    no file descriptors are passed. Note that sending file descriptors
+    to the service manager on messages that do not expect them (i.e.
+    without <literal>FDSTORE=1</literal>) they are immediately closed
+    on reception.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Return Value</title>
+
+    <para>On failure, these calls return a negative errno-style error
+    code. If <varname>$NOTIFY_SOCKET</varname> was not set and hence
+    no status data could be sent, 0 is returned. If the status was
+    sent, these functions return with a positive return value. In
+    order to support both, init systems that implement this scheme and
+    those which do not, it is generally recommended to ignore the
+    return value of this call.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Notes</title>
+
+    <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
+
+    <para>These functions send a single datagram with the
+    state string as payload to the <constant>AF_UNIX</constant> socket
+    referenced in the <varname>$NOTIFY_SOCKET</varname> environment
+    variable. If the first character of
+    <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
+    string is understood as Linux abstract namespace socket. The
+    datagram is accompanied by the process credentials of the sending
+    service, using SCM_CREDENTIALS.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Environment</title>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$NOTIFY_SOCKET</varname></term>
+
+        <listitem><para>Set by the service manager for supervised
+        processes for status and start-up completion notification.
+        This environment variable specifies the socket
+        <function>sd_notify()</function> talks to. See above for
+        details.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Examples</title>
+
+    <example>
+      <title>Start-up Notification</title>
+
+      <para>When a service finished starting up, it might issue the
+      following call to notify the service manager:</para>
+
+      <programlisting>sd_notify(0, "READY=1");</programlisting>
+    </example>
+
+    <example>
+      <title>Extended Start-up Notification</title>
+
+      <para>A service could send the following after completing
+      initialization:</para>
+
+      <programlisting>sd_notifyf(0, "READY=1\n"
+        "STATUS=Processing requests...\n"
+        "MAINPID=%lu",
+        (unsigned long) getpid());</programlisting>
+    </example>
+
+    <example>
+      <title>Error Cause Notification</title>
+
+      <para>A service could send the following shortly before exiting, on failure:</para>
+
+      <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
+        "ERRNO=%i",
+        strerror(errno),
+        errno);</programlisting>
+    </example>
+
+    <example>
+      <title>Store a File Descriptor in the Service Manager</title>
+
+      <para>To store an open file descriptor in the service manager,
+      in order to continue operation after a service restart without
+      losing state, use <literal>FDSTORE=1</literal>:</para>
+
+      <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
+    </example>
+  </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>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>