-<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//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/>.
--->
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<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>
<refname>sd_pid_notify</refname>
<refname>sd_pid_notifyf</refname>
<refname>sd_pid_notify_with_fds</refname>
+ <refname>sd_notify_barrier</refname>
<refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
</refnamediv>
<paramdef>const int *<parameter>fds</parameter></paramdef>
<paramdef>unsigned <parameter>n_fds</parameter></paramdef>
</funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_notify_barrier</function></funcdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>uint64_t <parameter>timeout</parameter></paramdef>
+ </funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<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>
+ <listitem><para>Tells the service manager that service startup is finished, or the service finished loading its
+ configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
+ 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>
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>
+ configuration. Reloads are propagated in the same way as they
+ are when initiated by the user.</para></listitem>
</varlistentry>
<varlistentry>
watchdog is enabled. </para></listitem>
</varlistentry>
+ <varlistentry>
+ <term>WATCHDOG=trigger</term>
+
+ <listitem><para>Tells the service manager that the service detected an internal error that should be handled by
+ the configured watchdog options. This will trigger the same behaviour as if <varname>WatchdogSec=</varname> is
+ enabled and the service did not send <literal>WATCHDOG=1</literal> in time. Note that
+ <varname>WatchdogSec=</varname> does not need to be enabled for <literal>WATCHDOG=trigger</literal> to trigger
+ the watchdog action. See
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+ information about the watchdog behavior. </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>
+
+ <varlistentry>
+ <term>EXTEND_TIMEOUT_USEC=…</term>
+
+ <listitem><para>Tells the service manager to extend the startup, runtime or shutdown service timeout
+ corresponding the current state. The value specified is a time in microseconds during which the service must
+ send a new message. A service timeout will occur if the message isn't received, but only if the runtime of the
+ current state is beyond the original maximum times of <varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>,
+ and <varname>TimeoutStopSec=</varname>.
+ See <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for effects on the service timeouts.</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>
+ <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 later be handed back using the usual file descriptor
+ passing logic at the next invocation of the service, see
+ <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This is
+ useful for implementing services that can restart after an explicit request or a crash without losing
+ state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
+ this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
+ in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
+ file descriptor. Note that the service manager will accept messages for a service only if its
+ <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If
+ <varname>FDPOLL=0</varname> is not set and the file descriptors sent are pollable (see
+ <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
+ <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
+ automatic removal from the store. 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 (pointing to the same
+ object) 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>FDSTOREREMOVE=1</term>
+
+ <listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
+ <varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</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
+ <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
+ file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
+ descriptors to remove. 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>
+ 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 arbitrary ASCII
+ characters except 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>
+ <term>FDPOLL=0</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>
+ <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, disables polling of the stored
+ file descriptors regardless of whether or not they are pollable. As this option disables automatic cleanup
+ of the stored file descriptors on EPOLLERR and EPOLLHUP, care must be taken to ensure proper manual cleanup.
+ Use of this option is not generally recommended except for when automatic cleanup has unwanted behavior such
+ as prematurely discarding file descriptors from the store.</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term>BARRIER=1</term>
+
+ <listitem><para>Tells the service manager that the client is explicitly requesting synchronization by means of
+ closing the file descriptor sent with this command. The service manager guarantees that the processing of a <varname>
+ BARRIER=1</varname> command will only happen after all previous notification messages sent before this command
+ have been processed. Hence, this command accompanied with a single file descriptor can be used to synchronize
+ against reception of all previous status messages. Note that this command cannot be mixed with other notifications,
+ and has to be sent in a separate message to the service manager, otherwise all assignments will be ignored. Note that
+ sending 0 or more than 1 file descriptor with this command is a violation of the protocol.</para></listitem>
+ </varlistentry>
</variablelist>
<para>It is recommended to prefix variable names that are not
attribute the message to the unit, and thus will ignore it, even if
<varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
+ <para>Hence, to eliminate all race conditions involving lookup of the client's unit and attribution of notifications
+ to units correctly, <function>sd_notify_barrier()</function> may be used. This call acts as a synchronization point
+ and ensures all notifications sent before this call have been picked up by the service manager when it returns
+ successfully. Use of <function>sd_notify_barrier()</function> is needed for clients which are not invoked by the
+ service manager, otherwise this synchronization mechanism is unnecessary for attribution of notifications to the
+ unit.</para>
+
<para><function>sd_notifyf()</function> is similar to
<function>sd_notify()</function> but takes a
<function>printf()</function>-like format string plus
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>
+
+ <para><function>sd_notify_barrier()</function> allows the caller to
+ synchronize against reception of previously sent notification messages
+ and uses the <literal>BARRIER=1</literal> command. It takes a relative
+ <varname>timeout</varname> value in microseconds which is passed to
+ <citerefentry><refentrytitle>ppoll</refentrytitle><manvolnum>2</manvolnum>
+ </citerefentry>. A value of UINT64_MAX is interpreted as infinite timeout.
+ </para>
</refsect1>
<refsect1>
<title>Return Value</title>
- <para>On failure, these calls return a negative errno-style error
- code. If <varname>$NOTIFY_SOCKET</varname> was not set and hence
- no status data could be sent, 0 is returned. If the status was
- sent, these functions return with a positive return value. In
- order to support both, init systems that implement this scheme and
- those which do not, it is generally recommended to ignore the
- return value of this call.</para>
+ <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
+ not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
+ positive value. In order to support both service managers that implement this scheme and those which do not, it is
+ generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
+ the notification message was enqueued properly, it does not reflect whether the message could be processed
+ successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
+ <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
+ above).</para>
</refsect1>
<refsect1>
<programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &fd, 1);</programlisting>
</example>
+
+ <example>
+ <title>Eliminating race conditions</title>
+
+ <para>When the client sending the notifications is not spawned
+ by the service manager, it may exit too quickly and the service
+ manager may fail to attribute them correctly to the unit. To
+ prevent such races, use <function>sd_notify_barrier()</function>
+ to synchronize against reception of all notifications sent before
+ this call is made.</para>
+
+ <programlisting>sd_notify(0, "READY=1");
+ /* set timeout to 5 seconds */
+ sd_notify_barrier(0, 5 * 1000000);
+ </programlisting>
+ </example>
</refsect1>
<refsect1>
projects / thirdparty / systemd.git / blobdiff