mirror of
https://github.com/systemd/systemd.git
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11a1589223
Files which are installed as-is (any .service and other unit files, .conf files, .policy files, etc), are left as is. My assumption is that SPDX identifiers are not yet that well known, so it's better to retain the extended header to avoid any doubt. I also kept any copyright lines. We can probably remove them, but it'd nice to obtain explicit acks from all involved authors before doing that.
415 lines
19 KiB
XML
415 lines
19 KiB
XML
<?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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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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SPDX-License-Identifier: LGPL-2.1+
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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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 by a service
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to notify the service manager about state changes. It can be used
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to send arbitrary information, encoded in an
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environment-block-like string. Most importantly, it can be used for
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start-up completion notification.</para>
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<para>If the <parameter>unset_environment</parameter> parameter is
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non-zero, <function>sd_notify()</function> will unset the
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<varname>$NOTIFY_SOCKET</varname> environment variable before
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returning (regardless of whether the function call itself
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succeeded or not). Further calls to
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<function>sd_notify()</function> will then fail, but the variable
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is no longer inherited by child processes.</para>
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<para>The <parameter>state</parameter> parameter should contain a
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newline-separated list of variable assignments, similar in style
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to an environment 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 manager that service startup is finished, or the service finished loading its
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configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
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set. Since there is little value in signaling non-readiness, the only value services should send is
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<literal>READY=1</literal> (i.e. <literal>READY=0</literal> is 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 that the service is
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reloading its configuration. This is useful to allow the
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service manager to track the service's internal state, and
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present it to the user. Note that a service that sends this
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notification must also send a <literal>READY=1</literal>
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notification when it completed reloading its
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configuration. Reloads are propagated in the same way as they
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are when initiated by the user.</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 that the service is
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beginning its shutdown. This is useful to allow the service
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manager to track the service's internal state, and present it
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to the 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 UTF-8 status string back
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to the service manager that describes the service state. This
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is free-form and can be used for various purposes: general
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state feedback, fsck-like programs could pass completion
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percentages and failing programs could pass a human-readable
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error message. Example: <literal>STATUS=Completed 66% of file
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system 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 errno-style error
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code, formatted as string. Example: <literal>ERRNO=2</literal>
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for 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 D-Bus error-style
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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 service, in
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case the service manager did not fork off the process itself.
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Example: <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 update the
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watchdog timestamp. This is the keep-alive ping that services
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need to issue in regular intervals if
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<varname>WatchdogSec=</varname> is 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 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 check whether the
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watchdog is enabled. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG_USEC=…</term>
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<listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
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Notice that this is not available when using <function>sd_event_set_watchdog()</function>
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or <function>sd_watchdog_enabled()</function>.
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Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
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</varlistentry>
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<varlistentry>
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<term>EXTEND_TIMEOUT_USEC=…</term>
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<listitem><para>Tells the service manager to extend the startup, runtime or shutdown service timeout
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corresponding the current state. The value specified is a time in microseconds during which the service must
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send a new message. A service timeout will occur if the message isn't received, but only if the runtime of the
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current state is beyond the original maximium times of <varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>,
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and <varname>TimeoutStopSec=</varname>.
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See <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for effects on the service timeouts.</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 descriptors in the service manager. File descriptors sent this way will
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be maintained per-service by the service manager and will later be handed back using the usual file descriptor
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passing logic at the next invocation of the service, see
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<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This is
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useful for implementing services that can restart after an explicit request or a crash without losing
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state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
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this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
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in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
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file descriptor. Note that the service manager will accept messages for a service only if its
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<varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If file
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descriptors sent are pollable (see
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<citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
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<constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
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automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
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which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
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object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
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to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDSTOREREMOVE=1</term>
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<listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
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<varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>FDNAME=…</term>
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<listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
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file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
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descriptors to remove. This name is passed to the service during activation, and may be queried using
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<citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
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descriptors submitted without this field set, will implicitly get the name <literal>stored</literal>
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assigned. Note that, if multiple file descriptors are submitted at once, the specified name will be assigned to
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all of them. In order to assign different names to submitted file descriptors, submit them in separate
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invocations of <function>sd_pid_notify_with_fds()</function>. The name may consist of arbitrary ASCII
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characters except control characters or <literal>:</literal>. It may not be longer than 255 characters. If a
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submitted name does not follow these restrictions, it is ignored.</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 are not
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listed above with <varname>X_</varname> to avoid namespace
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clashes.</para>
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<para>Note that systemd will accept status data sent from a
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service only if the <varname>NotifyAccess=</varname> option is
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correctly 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>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
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the sending process is still around at the time PID 1 processes the message, or if the sending process is
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explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
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off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
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<varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
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<function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
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attribute the message to the unit, and thus will ignore it, even if
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<varname>NotifyAccess=</varname><option>all</option> is set for it.</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 ID (PID) to
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use as originating PID for the message as first argument. This is
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useful to send notification messages on behalf of other processes,
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provided the appropriate privileges are available. If the PID
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argument is specified as 0, the process ID of the calling process
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is used, in which case the calls are fully equivalent to
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<function>sd_notify()</function> and
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<function>sd_notifyf()</function>.</para>
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<para><function>sd_pid_notify_with_fds()</function> is similar to
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<function>sd_pid_notify()</function> but takes an additional array
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of file descriptors. These file descriptors are sent along the
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notification message to the service manager. This is particularly
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useful for sending <literal>FDSTORE=1</literal> messages, as
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described above. The additional arguments are a pointer to the
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file descriptor array plus the number of file descriptors in the
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array. If the number of file descriptors is passed as 0, the call
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is fully equivalent to <function>sd_pid_notify()</function>, i.e.
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no file descriptors are passed. Note that sending file descriptors
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to the service manager on messages that do not expect them (i.e.
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without <literal>FDSTORE=1</literal>) they are immediately closed
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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 errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
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not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
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positive value. In order to support both service managers that implement this scheme and those which do not, it is
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generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
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the notification message was enqueued properly, it does not reflect whether the message could be processed
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successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
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<varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
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above).</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>These functions send a single datagram with the
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state string as payload to the <constant>AF_UNIX</constant> socket
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referenced in the <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
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string is understood as Linux abstract namespace socket. The
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datagram is accompanied by the process credentials of the sending
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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 for supervised
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processes for status and start-up completion notification.
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This environment variable specifies the socket
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<function>sd_notify()</function> talks to. 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>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 might issue the
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following call to notify 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 completing
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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 service manager,
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in order to continue operation after a service restart without
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losing state, use <literal>FDSTORE=1</literal>:</para>
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<programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &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>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_watchdog_enabled</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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</para>
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</refsect1>
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</refentry>
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