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| <!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 <systemd/sd-daemon.h></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, see |
| <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>. This is |
| useful for implementing services that can restart after an explicit request or a crash without losing |
| state. Any open sockets and other file descriptors which should not be closed during the restart may be stored |
| this way. Application state can either be serialized to a file in <filename>/run/</filename>, or better, stored |
| in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory |
| file descriptor. Note that the service manager will accept messages for a service only if its |
| <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see |
| <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If |
| <varname>FDPOLL=0</varname> is not set and the file descriptors sent are pollable (see |
| <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any |
| <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their |
| automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in |
| which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same |
| object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function> |
| to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>FDSTOREREMOVE=1</term> |
| |
| <listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with |
| <varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term>FDNAME=…</term> |
| |
| <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted |
| file descriptors. 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 <literal>BARRIER=1</literal> command. It takes a relative |
| <varname>timeout</varname> value in microseconds which is passed to |
| <citerefentry><refentrytitle>ppoll</refentrytitle><manvolnum>2</manvolnum> |
| </citerefentry>. A value of UINT64_MAX is interpreted as infinite timeout. |
| </para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Return Value</title> |
| |
| <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was |
| not set and hence no status 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(errno), |
| errno);</programlisting> |
| </example> |
| |
| <example> |
| <title>Store a File Descriptor in the Service Manager</title> |
| |
| <para>To store an open file descriptor in the service manager, |
| in order to continue operation after a service restart without |
| losing state, use <literal>FDSTORE=1</literal>:</para> |
| |
| <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &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> |
