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+<?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">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="sd_notify"
+ xmlns:xi="http://www.w3.org/2001/XInclude">
+
+ <refentryinfo>
+ <title>sd_notify</title>
+ <productname>systemd</productname>
+ </refentryinfo>
+
+ <refmeta>
+ <refentrytitle>sd_notify</refentrytitle>
+ <manvolnum>3</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>sd_notify</refname>
+ <refname>sd_notifyf</refname>
+ <refname>sd_pid_notify</refname>
+ <refname>sd_pid_notifyf</refname>
+ <refname>sd_pid_notify_with_fds</refname>
+ <refname>sd_notify_barrier</refname>
+ <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
+
+ <funcprototype>
+ <funcdef>int <function>sd_notify</function></funcdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>const char *<parameter>state</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_notifyf</function></funcdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>const char *<parameter>format</parameter></paramdef>
+ <paramdef>…</paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_pid_notify</function></funcdef>
+ <paramdef>pid_t <parameter>pid</parameter></paramdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>const char *<parameter>state</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_pid_notifyf</function></funcdef>
+ <paramdef>pid_t <parameter>pid</parameter></paramdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>const char *<parameter>format</parameter></paramdef>
+ <paramdef>…</paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
+ <paramdef>pid_t <parameter>pid</parameter></paramdef>
+ <paramdef>int <parameter>unset_environment</parameter></paramdef>
+ <paramdef>const char *<parameter>state</parameter></paramdef>
+ <paramdef>const int *<parameter>fds</parameter></paramdef>
+ <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
+ </funcprototype>
+
+ <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>
+
+ <refsect1>
+ <title>Description</title>
+ <para><function>sd_notify()</function> may be called by a service
+ to notify the service manager about state changes. It can be used
+ to send arbitrary information, encoded in an
+ environment-block-like string. Most importantly, it can be used for
+ start-up completion notification.</para>
+
+ <para>If the <parameter>unset_environment</parameter> parameter is
+ non-zero, <function>sd_notify()</function> will unset the
+ <varname>$NOTIFY_SOCKET</varname> environment variable before
+ returning (regardless of whether the function call itself
+ succeeded or not). Further calls to
+ <function>sd_notify()</function> will then fail, but the variable
+ is no longer inherited by child processes.</para>
+
+ <para>The <parameter>state</parameter> parameter should contain a
+ newline-separated list of variable assignments, similar in style
+ to an environment block. A trailing newline is implied if none is
+ specified. The string may contain any kind of variable
+ assignments, but the following shall be considered
+ well-known:</para>
+
+ <variablelist>
+ <varlistentry>
+ <term>READY=1</term>
+
+ <listitem><para>Tells the service manager that service startup is finished, 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>
+ <term>RELOADING=1</term>
+
+ <listitem><para>Tells the service manager that the service is
+ reloading its configuration. This is useful to allow the
+ service manager to track the service's internal state, and
+ present it to the user. Note that a service that sends this
+ notification must also send a <literal>READY=1</literal>
+ notification when it completed reloading its
+ configuration. Reloads are propagated in the same way as they
+ are when initiated by the user.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>STOPPING=1</term>
+
+ <listitem><para>Tells the service manager that the service is
+ beginning its shutdown. This is useful to allow the service
+ manager to track the service's internal state, and present it
+ to the user.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>STATUS=…</term>
+
+ <listitem><para>Passes a single-line UTF-8 status string back
+ to the service manager that describes the service state. This
+ is free-form and can be used for various purposes: general
+ state feedback, fsck-like programs could pass completion
+ percentages and failing programs could pass a human-readable
+ error message. Example: <literal>STATUS=Completed 66% of file
+ system check…</literal></para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>ERRNO=…</term>
+
+ <listitem><para>If a service fails, the errno-style error
+ code, formatted as string. Example: <literal>ERRNO=2</literal>
+ for ENOENT.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>BUSERROR=…</term>
+
+ <listitem><para>If a service fails, the D-Bus error-style
+ error code. Example:
+ <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>MAINPID=…</term>
+
+ <listitem><para>The main process ID (PID) of the service, in
+ case the service manager did not fork off the process itself.
+ Example: <literal>MAINPID=4711</literal></para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>WATCHDOG=1</term>
+
+ <listitem><para>Tells the service manager to update the
+ watchdog timestamp. This is the keep-alive ping that services
+ need to issue in regular intervals if
+ <varname>WatchdogSec=</varname> is enabled for it. See
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for information how to enable this functionality and
+ <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ for the details of how the service can check whether the
+ watchdog is enabled. </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term>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 later be handed back using the usual file descriptor
+ passing logic at the next invocation of the service (e.g. when it is restarted), 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. When a service is stopped, its file descriptor
+ store is discarded and all file descriptors in it are closed. 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. 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 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>FDPOLL=0</term>
+
+ <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
+ listed above with <varname>X_</varname> to avoid namespace
+ clashes.</para>
+
+ <para>Note that systemd will accept status data sent from a
+ service only if the <varname>NotifyAccess=</varname> option is
+ correctly set in the service definition file. See
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ for details.</para>
+
+ <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
+ the sending process is still around at the time PID 1 processes the message, or if the sending process is
+ explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
+ off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
+ <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
+ <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
+ 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
+ arguments.</para>
+
+ <para><function>sd_pid_notify()</function> and
+ <function>sd_pid_notifyf()</function> are similar to
+ <function>sd_notify()</function> and
+ <function>sd_notifyf()</function> but take a process ID (PID) to
+ use as originating PID for the message as first argument. This is
+ useful to send notification messages on behalf of other processes,
+ provided the appropriate privileges are available. If the PID
+ argument is specified as 0, the process ID of the calling process
+ is used, in which case the calls are fully equivalent to
+ <function>sd_notify()</function> and
+ <function>sd_notifyf()</function>.</para>
+
+ <para><function>sd_pid_notify_with_fds()</function> is similar to
+ <function>sd_pid_notify()</function> but takes an additional array
+ of file descriptors. These file descriptors are sent along the
+ notification message to the service manager. This is particularly
+ useful for sending <literal>FDSTORE=1</literal> messages, as
+ described above. The additional arguments are a pointer to the
+ file descriptor array plus the number of file descriptors in the
+ array. If the number of file descriptors is passed as 0, the call
+ is fully equivalent to <function>sd_pid_notify()</function>, i.e.
+ no file descriptors are passed. Note that sending file descriptors
+ to the service manager on messages that do not expect them (i.e.
+ without <literal>FDSTORE=1</literal>) they are immediately closed
+ on reception.</para>
+
+ <para><function>sd_notify_barrier()</function> allows the caller to
+ synchronize against reception of previously sent notification messages
+ and uses the <varname>BARRIER=1</varname> 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 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"/>
+
+ <para>These functions send a single datagram with the
+ state string as payload to the <constant>AF_UNIX</constant> socket
+ referenced in the <varname>$NOTIFY_SOCKET</varname> environment
+ variable. If the first character of
+ <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
+ string is understood as Linux abstract namespace socket. The
+ datagram is accompanied by the process credentials of the sending
+ service, using SCM_CREDENTIALS.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Environment</title>
+
+ <variablelist class='environment-variables'>
+ <varlistentry>
+ <term><varname>$NOTIFY_SOCKET</varname></term>
+
+ <listitem><para>Set by the service manager for supervised
+ processes for status and start-up completion notification.
+ This environment variable specifies the socket
+ <function>sd_notify()</function> talks to. See above for
+ details.</para></listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Examples</title>
+
+ <example>
+ <title>Start-up Notification</title>
+
+ <para>When a service finished starting up, it might issue the
+ following call to notify the service manager:</para>
+
+ <programlisting>sd_notify(0, "READY=1");</programlisting>
+ </example>
+
+ <example>
+ <title>Extended Start-up Notification</title>
+
+ <para>A service could send the following after completing
+ initialization:</para>
+
+ <programlisting>sd_notifyf(0, "READY=1\n"
+ "STATUS=Processing requests…\n"
+ "MAINPID=%lu",
+ (unsigned long) getpid());</programlisting>
+ </example>
+
+ <example>
+ <title>Error Cause Notification</title>
+
+ <para>A service could send the following shortly before exiting, on failure:</para>
+
+ <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
+ "ERRNO=%i",
+ strerror_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", &amp;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>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ </para>
+ </refsect1>
+
+</refentry>