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620 lines
32 KiB
XML
620 lines
32 KiB
XML
<?xml version='1.0'?>
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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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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</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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<refname>sd_pid_notifyf_with_fds</refname>
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<refname>sd_notify_barrier</refname>
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<refname>sd_pid_notify_barrier</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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<funcprototype>
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<funcdef>int <function>sd_pid_notifyf_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 int *<parameter>fds</parameter></paramdef>
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<paramdef>size_t <parameter>n_fds</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_notify_barrier</function></funcdef>
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<paramdef>int <parameter>unset_environment</parameter></paramdef>
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<paramdef>uint64_t <parameter>timeout</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_pid_notify_barrier</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>uint64_t <parameter>timeout</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 to notify the service manager about
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state changes. It can be used to send arbitrary information, encoded in an environment-block-like string.
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Most importantly, it can be used for start-up or reload completion notifications.</para>
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<para>If the <parameter>unset_environment</parameter> parameter is non-zero,
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<function>sd_notify()</function> will unset the <varname>$NOTIFY_SOCKET</varname> environment variable
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before returning (regardless of whether the function call itself succeeded or not). Further calls to
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<function>sd_notify()</function> will then silently do nothing, and the variable is no longer inherited
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by child processes.</para>
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<para>The <parameter>state</parameter> parameter should contain a newline-separated list of variable
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assignments, similar in style 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 assignments, but see the next section
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for a list of assignments understood by the service manager.</para>
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<para>Note that systemd will accept status data sent from a service only if the
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<varname>NotifyAccess=</varname> option is correctly set in the service definition file. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
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details.</para>
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<para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only
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if either the sending process is still around at the time PID 1 processes the message, or if the sending
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process is explicitly runtime-tracked by the service manager. The latter is the case if the service
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manager originally forked off the process, i.e. on all processes that match
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<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
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sends an <function>sd_notify()</function> message and immediately exits, the service manager might not be
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able to properly 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>Hence, to eliminate all race conditions involving lookup of the client's unit and attribution of
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notifications to units correctly, <function>sd_notify_barrier()</function> may be used. This call acts as
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a synchronization point and ensures all notifications sent before this call have been picked up by the
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service manager when it returns successfully. Use of <function>sd_notify_barrier()</function> is needed
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for clients which are not invoked by the service manager, otherwise this synchronization mechanism is
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unnecessary for attribution of notifications to the unit.</para>
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<para><function>sd_notifyf()</function> is similar to <function>sd_notify()</function> but takes a
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<function>printf()</function>-like format string plus arguments.</para>
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<para><function>sd_pid_notify()</function> and <function>sd_pid_notifyf()</function> are similar to
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<function>sd_notify()</function> and <function>sd_notifyf()</function> but take a process ID (PID) to use
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as originating PID for the message as first argument. This is useful to send notification messages on
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behalf of other processes, provided the appropriate privileges are available. If the PID argument is
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specified as 0, the process ID of the calling process is used, in which case the calls are fully
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equivalent to <function>sd_notify()</function> and <function>sd_notifyf()</function>.</para>
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<para><function>sd_pid_notify_with_fds()</function> is similar to <function>sd_pid_notify()</function>
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but takes an additional array of file descriptors. These file descriptors are sent along the notification
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message to the service manager. This is particularly useful for sending <literal>FDSTORE=1</literal>
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messages, as described above. The additional arguments are a pointer to the file descriptor array plus
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the number of file descriptors in the 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. no file descriptors are passed. Note
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that file descriptors sent to the service manager on a message without <literal>FDSTORE=1</literal> are
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immediately closed on reception.</para>
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<para><function>sd_pid_notifyf_with_fds()</function> is a combination of
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<function>sd_pid_notify_with_fds()</function> and <function>sd_notifyf()</function>, i.e. it accepts both
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a PID and a set of file descriptors as input, and processes a format string to generate the state
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string.</para>
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<para><function>sd_notify_barrier()</function> allows the caller to synchronize against reception of
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previously sent notification messages and uses the <varname>BARRIER=1</varname> command. It takes a
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relative <varname>timeout</varname> value in microseconds which is passed to
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<citerefentry><refentrytitle>ppoll</refentrytitle><manvolnum>2</manvolnum>
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</citerefentry>. A value of UINT64_MAX is interpreted as infinite timeout.</para>
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<para><function>sd_pid_notify_barrier()</function> is just like <function>sd_notify_barrier()</function>,
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but allows specifying the originating PID for the notification message.</para>
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</refsect1>
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<refsect1>
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<title>Well-known assignments</title>
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<para>The following assignments have a defined meaning:</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
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re-loading its configuration. This is only used by systemd if the service definition file has
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<varname>Type=notify</varname> or <varname>Type=notify-reload</varname> set. Since there is little
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value in signaling non-readiness, the only value services should send is <literal>READY=1</literal>
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(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 beginning to reload its configuration.
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This is useful to allow the service manager to track the service's internal state, and present it to
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the user. Note that a service that sends this notification must also send a
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<literal>READY=1</literal> notification when it completed reloading its configuration. Reloads the
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service manager is notified about with this mechanisms are propagated in the same way as they are
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when originally initiated through the service manager. This message is particularly relevant for
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<varname>Type=notify-reload</varname> services, to inform the service manager that the request to
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reload the service has been received and is now being processed.</para>
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<xi:include href="version-info.xml" xpointer="v217"/></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 beginning its shutdown. This is useful
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to allow the service manager to track the service's internal state, and present it to the user.
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</para>
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<xi:include href="version-info.xml" xpointer="v217"/></listitem>
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</varlistentry>
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<varlistentry>
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<term>MONOTONIC_USEC=…</term>
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<listitem><para>A field carrying the monotonic timestamp (as per
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<constant>CLOCK_MONOTONIC</constant>) formatted in decimal in μs, when the notification message was
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generated by the client. This is typically used in combination with <literal>RELOADING=1</literal>,
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to allow the service manager to properly synchronize reload cycles. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details, specifically <literal>Type=notify-reload</literal>.</para>
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<xi:include href="version-info.xml" xpointer="v253"/></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 to the service manager that describes
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the service state. This is free-form and can be used for various purposes: general state feedback,
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fsck-like programs could pass completion percentages and failing programs could pass a human-readable
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error message. Example: <literal>STATUS=Completed 66% of file system check…</literal></para>
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<xi:include href="version-info.xml" xpointer="v233"/></listitem>
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</varlistentry>
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<varlistentry>
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<term>NOTIFYACCESS=…</term>
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<listitem><para>Reset the access to the service status notification socket during runtime, overriding
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<varname>NotifyAccess=</varname> setting in the service unit file. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details, specifically <literal>NotifyAccess=</literal> for a list of accepted values.
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</para>
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<xi:include href="version-info.xml" xpointer="v254"/></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 code, formatted as string. Example:
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<literal>ERRNO=2</literal> for ENOENT.</para>
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<xi:include href="version-info.xml" xpointer="v233"/></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 error code. Example:
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<literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal>.</para>
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<xi:include href="version-info.xml" xpointer="v233"/></listitem>
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</varlistentry>
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<varlistentry>
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<term>VARLINKERROR=…</term>
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<listitem><para>If a service fails, the Varlink error-style error code. Example:
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<literal>VARLINKERROR=org.varlink.service.InvalidParameter</literal>.</para>
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<xi:include href="version-info.xml" xpointer="v257"/></listitem>
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</varlistentry>
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<varlistentry>
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<term>EXIT_STATUS=…</term>
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<listitem><para>The exit status of a service or the manager itself. Note that
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<command>systemd</command> currently does not consume this value when sent by services, so this
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assignment is only informational. The manager will send this notification to <emphasis>its</emphasis>
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notification socket, which may be used to collect an exit status from the system (a container or
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VM) as it shuts down. For example,
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<citerefentry project='debian'><refentrytitle>mkosi</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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makes use of this. The value to return may be set via the
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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<command>exit</command> verb.</para>
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<xi:include href="version-info.xml" xpointer="v254"/></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 case the service manager did not fork
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off the process itself. Example: <literal>MAINPID=4711</literal>.</para>
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<xi:include href="version-info.xml" xpointer="v233"/></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 watchdog timestamp. This is the keep-alive
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ping that services need to issue in regular intervals if <varname>WatchdogSec=</varname> is enabled
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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 watchdog is enabled. </para></listitem>
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</varlistentry>
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<varlistentry>
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<term>WATCHDOG=trigger</term>
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<listitem><para>Tells the service manager that the service detected an internal error that should be
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handled by the configured watchdog options. This will trigger the same behaviour as if
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<varname>WatchdogSec=</varname> is enabled and the service did not send <literal>WATCHDOG=1</literal>
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in time. Note that <varname>WatchdogSec=</varname> does not need to be enabled for
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<literal>WATCHDOG=trigger</literal> to trigger the watchdog action. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for information about the watchdog behavior. </para>
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<xi:include href="version-info.xml" xpointer="v243"/></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. Notice that this is not
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available when using <function>sd_event_set_watchdog()</function> or
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<function>sd_watchdog_enabled()</function>. Example :
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<literal>WATCHDOG_USEC=20000000</literal></para>
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<xi:include href="version-info.xml" xpointer="v233"/></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
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service must send a new message. A service timeout will occur if the message isn't received, but only
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if the runtime of the current state is beyond the original maximum times of
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<varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>, and
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<varname>TimeoutStopSec=</varname>. See
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for effects on the service timeouts.</para>
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<xi:include href="version-info.xml" xpointer="v236"/></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>Store file descriptors in the service manager. File descriptors sent this way will be
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held for the service by the service manager and will later be handed back using the usual file
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descriptor passing logic at the next start or restart of the service, see
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<citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
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Any open sockets and other file descriptors which should not be closed during a restart may be stored
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this way. When a service is stopped, its file descriptor store is discarded and all file descriptors
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in it are closed, except when overridden with <varname>FileDescriptorStorePreserve=</varname>, see
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<citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para>
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<para>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>).
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The service manager will set the <varname>$FDSTORE</varname> environment variable for services that
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have the file descriptor store enabled, see
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para>
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<para>If <varname>FDPOLL=0</varname> is not set and the file descriptors are pollable (see
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<citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then
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any <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in
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their automatic removal from the store.</para>
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<para>Multiple sets of file descriptors may be sent in separate messages, in which case the sets are
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combined. The service manager removes duplicate file descriptors (those pointing to the same object)
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before passing them to the service.</para>
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<para>This functionality should be used to implement services that can restart after an explicit
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request or a crash without losing state. Application state can either be serialized to a file in
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<filename>/run/</filename>, or better, stored in a
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<citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry>
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memory file descriptor. Use <function>sd_pid_notify_with_fds()</function> to send messages with
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<literal>FDSTORE=1</literal>. It is recommended to combine <varname>FDSTORE=</varname> with
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<varname>FDNAME=</varname> to make it easier to manage the stored file descriptors.</para>
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<para>For further information on the file descriptor store see the <ulink
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url="https://systemd.io/FILE_DESCRIPTOR_STORE">File Descriptor Store</ulink> overview.</para>
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<xi:include href="version-info.xml" xpointer="v219"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v236"/></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. 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 will be called <literal>stored</literal>.</para>
|
|
|
|
<para>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>
|
|
|
|
<para>Note that if multiple file descriptors are submitted in a single message, the specified name
|
|
will be used for all of them. In order to assign different names to submitted file descriptors,
|
|
submit them in separate messages.</para>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v233"/></listitem>
|
|
</varlistentry>
|
|
|
|
<varlistentry>
|
|
<term>FDPOLL=0</term>
|
|
|
|
<listitem><para>When used in combination with <varname>FDSTORE=1</varname>, disables polling of the
|
|
submitted file descriptors regardless of whether or not they are pollable. As this option disables
|
|
automatic cleanup of the submitted 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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v246"/></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>
|
|
|
|
<xi:include href="version-info.xml" xpointer="v246"/></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
|
|
<para>The notification messages sent by services are interpreted by the service manager. Unknown
|
|
assignments are ignored. Thus, it is safe (but often without effect) to send assignments which are not
|
|
in this list. The protocol is extensible, but care should be taken to ensure private extensions are
|
|
recognizable as such. Specifically, it is recommend to prefix them with <literal>X_</literal> followed by
|
|
some namespace identifier. The service manager also sends some messages to <emphasis>its</emphasis>
|
|
notification socket, which may then consumed by a supervising machine or container manager further up the
|
|
stack. The service manager sends a number of extension fields, for example
|
|
<varname>X_SYSTEMD_UNIT_ACTIVE=</varname>, for details see
|
|
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Return Value</title>
|
|
|
|
<para>On failure, these calls return a negative errno-style error code. If
|
|
<varname>$NOTIFY_SOCKET</varname> was not set and hence no status message could be sent, 0 is
|
|
returned. If the status was sent, these functions return a positive value. In order to support both
|
|
service managers that implement this scheme and those which do not, it is generally recommended to ignore
|
|
the return value of this call. Note that the return value simply indicates whether the notification
|
|
message was enqueued properly, it does not reflect whether the message could be processed
|
|
successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
|
|
<varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file
|
|
descriptors (see above).</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Notes</title>
|
|
|
|
<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
|
|
<xi:include href="threads-aware.xml" xpointer="getenv"/>
|
|
|
|
<para>These functions send a single datagram with the state string as payload to the socket referenced in
|
|
the <varname>$NOTIFY_SOCKET</varname> environment variable. If the first character of
|
|
<varname>$NOTIFY_SOCKET</varname> is <literal>/</literal> or <literal>@</literal>, the string is
|
|
understood as an <constant>AF_UNIX</constant> or Linux abstract namespace socket (respectively), and in
|
|
both cases the datagram is accompanied by the process credentials of the sending service, using
|
|
SCM_CREDENTIALS. If the string starts with <literal>vsock:</literal> then the string is understood as an
|
|
<constant>AF_VSOCK</constant> address, which is useful for hypervisors/VMMs or other processes on the
|
|
host to receive a notification when a virtual machine has finished booting. Note that in case the
|
|
hypervisor does not support <constant>SOCK_DGRAM</constant> over <constant>AF_VSOCK</constant>,
|
|
<constant>SOCK_SEQPACKET</constant> will be used instead. <literal>vsock-stream</literal>,
|
|
<literal>vsock-dgram</literal> and <literal>vsock-seqpacket</literal> can be used instead of
|
|
<literal>vsock</literal> to force usage of the corresponding socket type. The address should be in the
|
|
form: <literal>vsock:CID:PORT</literal>. Note that unlike other uses of vsock, the CID is mandatory and
|
|
cannot be <literal>VMADDR_CID_ANY</literal>. Note that PID1 will send the VSOCK packets from a
|
|
privileged port (i.e.: lower than 1024), as an attempt to address concerns that unprivileged processes in
|
|
the guest might try to send malicious notifications to the host, driving it to make destructive decisions
|
|
based on them.</para>
|
|
|
|
<refsect2>
|
|
<title>Standalone Implementations</title>
|
|
<para>Note that, while using this library should be preferred in order to avoid code duplication, it is
|
|
also possible to reimplement the simple readiness notification protocol without external dependencies,
|
|
as demonstrated in the following self-contained examples from several languages:</para>
|
|
<refsect3>
|
|
<title>C</title>
|
|
<programlisting><xi:include href="notify-selfcontained-example.c" parse="text"/></programlisting>
|
|
</refsect3>
|
|
<refsect3>
|
|
<title>Python</title>
|
|
<programlisting><xi:include href="notify-selfcontained-example.py" parse="text"/></programlisting>
|
|
</refsect3>
|
|
</refsect2>
|
|
</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_r(errnum, (char[1024]){}, 1024),
|
|
errnum);</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", &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>
|
|
<title>History</title>
|
|
<para><function>sd_pid_notify()</function>,
|
|
<function>sd_pid_notifyf()</function>, and
|
|
<function>sd_pid_notify_with_fds()</function> were added in version 219.</para>
|
|
<para><function>sd_notify_barrier()</function> was added in version 246.</para>
|
|
<para><function>sd_pid_notifyf_with_fds()</function> and
|
|
<function>sd_pid_notify_barrier()</function> were added in version 254.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para><simplelist type="inline">
|
|
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
|
|
</simplelist></para>
|
|
</refsect1>
|
|
|
|
</refentry>
|