man/sd_notify.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="sd_notify"
   7   xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>sd_notify</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>sd_notify</refentrytitle>
  16     <manvolnum>3</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>sd_notify</refname>
  21     <refname>sd_notifyf</refname>
  22     <refname>sd_pid_notify</refname>
  23     <refname>sd_pid_notifyf</refname>
  24     <refname>sd_pid_notify_with_fds</refname>
  25     <refname>sd_notify_barrier</refname>
  26     <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
  27   </refnamediv>
  28
  29   <refsynopsisdiv>
  30     <funcsynopsis>
  31       <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  32
  33       <funcprototype>
  34         <funcdef>int <function>sd_notify</function></funcdef>
  35         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  36         <paramdef>const char *<parameter>state</parameter></paramdef>
  37       </funcprototype>
  38
  39       <funcprototype>
  40         <funcdef>int <function>sd_notifyf</function></funcdef>
  41         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  42         <paramdef>const char *<parameter>format</parameter></paramdef>
  43         <paramdef>…</paramdef>
  44       </funcprototype>
  45
  46       <funcprototype>
  47         <funcdef>int <function>sd_pid_notify</function></funcdef>
  48         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  49         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  50         <paramdef>const char *<parameter>state</parameter></paramdef>
  51       </funcprototype>
  52
  53       <funcprototype>
  54         <funcdef>int <function>sd_pid_notifyf</function></funcdef>
  55         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  56         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  57         <paramdef>const char *<parameter>format</parameter></paramdef>
  58         <paramdef>…</paramdef>
  59       </funcprototype>
  60
  61       <funcprototype>
  62         <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
  63         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  64         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  65         <paramdef>const char *<parameter>state</parameter></paramdef>
  66         <paramdef>const int *<parameter>fds</parameter></paramdef>
  67         <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
  68       </funcprototype>
  69
  70       <funcprototype>
  71         <funcdef>int <function>sd_notify_barrier</function></funcdef>
  72         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  73         <paramdef>uint64_t <parameter>timeout</parameter></paramdef>
  74       </funcprototype>
  75     </funcsynopsis>
  76   </refsynopsisdiv>
  77
  78   <refsect1>
  79     <title>Description</title>
  80     <para><function>sd_notify()</function> may be called by a service
  81     to notify the service manager about state changes. It can be used
  82     to send arbitrary information, encoded in an
  83     environment-block-like string. Most importantly, it can be used for
  84     start-up completion notification.</para>
  85
  86     <para>If the <parameter>unset_environment</parameter> parameter is
  87     non-zero, <function>sd_notify()</function> will unset the
  88     <varname>$NOTIFY_SOCKET</varname> environment variable before
  89     returning (regardless of whether the function call itself
  90     succeeded or not). Further calls to
  91     <function>sd_notify()</function> will then fail, but the variable
  92     is no longer inherited by child processes.</para>
  93
  94     <para>The <parameter>state</parameter> parameter should contain a
  95     newline-separated list of variable assignments, similar in style
  96     to an environment block. A trailing newline is implied if none is
  97     specified. The string may contain any kind of variable
  98     assignments, but the following shall be considered
  99     well-known:</para>
 100
 101     <variablelist>
 102       <varlistentry>
 103         <term>READY=1</term>
 104
 105         <listitem><para>Tells the service manager that service startup is finished, or the service finished loading its
 106         configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
 107         set. Since there is little value in signaling non-readiness, the only value services should send is
 108         <literal>READY=1</literal> (i.e.  <literal>READY=0</literal> is not defined).</para></listitem>
 109       </varlistentry>
 110
 111       <varlistentry>
 112         <term>RELOADING=1</term>
 113
 114         <listitem><para>Tells the service manager that the service is
 115         reloading its configuration. This is useful to allow the
 116         service manager to track the service's internal state, and
 117         present it to the user. Note that a service that sends this
 118         notification must also send a <literal>READY=1</literal>
 119         notification when it completed reloading its
 120         configuration. Reloads are propagated in the same way as they
 121         are when initiated by the user.</para></listitem>
 122       </varlistentry>
 123
 124       <varlistentry>
 125         <term>STOPPING=1</term>
 126
 127         <listitem><para>Tells the service manager that the service is
 128         beginning its shutdown. This is useful to allow the service
 129         manager to track the service's internal state, and present it
 130         to the user.</para></listitem>
 131       </varlistentry>
 132
 133       <varlistentry>
 134         <term>STATUS=…</term>
 135
 136         <listitem><para>Passes a single-line UTF-8 status string back
 137         to the service manager that describes the service state. This
 138         is free-form and can be used for various purposes: general
 139         state feedback, fsck-like programs could pass completion
 140         percentages and failing programs could pass a human-readable
 141         error message. Example: <literal>STATUS=Completed 66% of file
 142         system check…</literal></para></listitem>
 143       </varlistentry>
 144
 145       <varlistentry>
 146         <term>ERRNO=…</term>
 147
 148         <listitem><para>If a service fails, the errno-style error
 149         code, formatted as string. Example: <literal>ERRNO=2</literal>
 150         for ENOENT.</para></listitem>
 151       </varlistentry>
 152
 153       <varlistentry>
 154         <term>BUSERROR=…</term>
 155
 156         <listitem><para>If a service fails, the D-Bus error-style
 157         error code. Example:
 158         <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 159       </varlistentry>
 160
 161       <varlistentry>
 162         <term>MAINPID=…</term>
 163
 164         <listitem><para>The main process ID (PID) of the service, in
 165         case the service manager did not fork off the process itself.
 166         Example: <literal>MAINPID=4711</literal></para></listitem>
 167       </varlistentry>
 168
 169       <varlistentry>
 170         <term>WATCHDOG=1</term>
 171
 172         <listitem><para>Tells the service manager to update the
 173         watchdog timestamp. This is the keep-alive ping that services
 174         need to issue in regular intervals if
 175         <varname>WatchdogSec=</varname> is enabled for it. See
 176         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 177         for information how to enable this functionality and
 178         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 179         for the details of how the service can check whether the
 180         watchdog is enabled. </para></listitem>
 181       </varlistentry>
 182
 183       <varlistentry>
 184         <term>WATCHDOG=trigger</term>
 185
 186         <listitem><para>Tells the service manager that the service detected an internal error that should be handled by
 187         the configured watchdog options. This will trigger the same behaviour as if <varname>WatchdogSec=</varname> is
 188         enabled and the service did not send <literal>WATCHDOG=1</literal> in time. Note that
 189         <varname>WatchdogSec=</varname> does not need to be enabled for <literal>WATCHDOG=trigger</literal> to trigger
 190         the watchdog action. See
 191         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 192         information about the watchdog behavior. </para></listitem>
 193       </varlistentry>
 194
 195       <varlistentry>
 196         <term>WATCHDOG_USEC=…</term>
 197
 198         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 199         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 200         or <function>sd_watchdog_enabled()</function>.
 201         Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
 202       </varlistentry>
 203
 204       <varlistentry>
 205         <term>EXTEND_TIMEOUT_USEC=…</term>
 206
 207         <listitem><para>Tells the service manager to extend the startup, runtime or shutdown service timeout
 208         corresponding the current state. The value specified is a time in microseconds during which the service must
 209         send a new message. A service timeout will occur if the message isn't received, but only if the runtime of the
 210         current state is beyond the original maximum times of <varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>,
 211         and <varname>TimeoutStopSec=</varname>.
 212         See <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 213         for effects on the service timeouts.</para></listitem>
 214       </varlistentry>
 215
 216       <varlistentry>
 217         <term>FDSTORE=1</term>
 218
 219         <listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
 220         be maintained per-service by the service manager and will later be handed back using the usual file descriptor
 221         passing logic at the next invocation of the service, see
 222         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.  This is
 223         useful for implementing services that can restart after an explicit request or a crash without losing
 224         state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
 225         this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
 226         in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
 227         file descriptor. Note that the service manager will accept messages for a service only if its
 228         <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
 229         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If
 230         <varname>FDPOLL=0</varname> is not set and the file descriptors sent are pollable (see
 231         <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
 232         <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
 233         automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
 234         which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
 235         object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
 236         to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
 237       </varlistentry>
 238
 239       <varlistentry>
 240         <term>FDSTOREREMOVE=1</term>
 241
 242         <listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
 243         <varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem>
 244       </varlistentry>
 245
 246       <varlistentry>
 247         <term>FDNAME=…</term>
 248
 249         <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
 250         file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
 251         descriptors to remove. This name is passed to the service during activation, and may be queried using
 252         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 253         descriptors submitted without this field set, will implicitly get the name <literal>stored</literal>
 254         assigned. Note that, if multiple file descriptors are submitted at once, the specified name will be assigned to
 255         all of them. In order to assign different names to submitted file descriptors, submit them in separate
 256         invocations of <function>sd_pid_notify_with_fds()</function>. The name may consist of arbitrary ASCII
 257         characters except control characters or <literal>:</literal>. It may not be longer than 255 characters. If a
 258         submitted name does not follow these restrictions, it is ignored.</para></listitem>
 259       </varlistentry>
 260
 261       <varlistentry>
 262         <term>FDPOLL=0</term>
 263
 264         <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, disables polling of the stored
 265         file descriptors regardless of whether or not they are pollable. As this option disables automatic cleanup
 266         of the stored file descriptors on EPOLLERR and EPOLLHUP, care must be taken to ensure proper manual cleanup.
 267         Use of this option is not generally recommended except for when automatic cleanup has unwanted behavior such
 268         as prematurely discarding file descriptors from the store.</para></listitem>
 269       </varlistentry>
 270
 271       <varlistentry>
 272         <term>BARRIER=1</term>
 273
 274         <listitem><para>Tells the service manager that the client is explicitly requesting synchronization by means of
 275         closing the file descriptor sent with this command. The service manager guarantees that the processing of a <varname>
 276         BARRIER=1</varname> command will only happen after all previous notification messages sent before this command
 277         have been processed. Hence, this command accompanied with a single file descriptor can be used to synchronize
 278         against reception of all previous status messages. Note that this command cannot be mixed with other notifications,
 279         and has to be sent in a separate message to the service manager, otherwise all assignments will be ignored. Note that
 280         sending 0 or more than 1 file descriptor with this command is a violation of the protocol.</para></listitem>
 281       </varlistentry>
 282     </variablelist>
 283
 284     <para>It is recommended to prefix variable names that are not
 285     listed above with <varname>X_</varname> to avoid namespace
 286     clashes.</para>
 287
 288     <para>Note that systemd will accept status data sent from a
 289     service only if the <varname>NotifyAccess=</varname> option is
 290     correctly set in the service definition file. See
 291     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 292     for details.</para>
 293
 294     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
 295     the sending process is still around at the time PID 1 processes the message, or if the sending process is
 296     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
 297     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
 298     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
 299     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
 300     attribute the message to the unit, and thus will ignore it, even if
 301     <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
 302
 303     <para>Hence, to eliminate all race conditions involving lookup of the client's unit and attribution of notifications
 304     to units correctly, <function>sd_notify_barrier()</function> may be used. This call acts as a synchronization point
 305     and ensures all notifications sent before this call have been picked up by the service manager when it returns
 306     successfully. Use of <function>sd_notify_barrier()</function> is needed for clients which are not invoked by the
 307     service manager, otherwise this synchronization mechanism is unnecessary for attribution of notifications to the
 308     unit.</para>
 309
 310     <para><function>sd_notifyf()</function> is similar to
 311     <function>sd_notify()</function> but takes a
 312     <function>printf()</function>-like format string plus
 313     arguments.</para>
 314
 315     <para><function>sd_pid_notify()</function> and
 316     <function>sd_pid_notifyf()</function> are similar to
 317     <function>sd_notify()</function> and
 318     <function>sd_notifyf()</function> but take a process ID (PID) to
 319     use as originating PID for the message as first argument. This is
 320     useful to send notification messages on behalf of other processes,
 321     provided the appropriate privileges are available. If the PID
 322     argument is specified as 0, the process ID of the calling process
 323     is used, in which case the calls are fully equivalent to
 324     <function>sd_notify()</function> and
 325     <function>sd_notifyf()</function>.</para>
 326
 327     <para><function>sd_pid_notify_with_fds()</function> is similar to
 328     <function>sd_pid_notify()</function> but takes an additional array
 329     of file descriptors. These file descriptors are sent along the
 330     notification message to the service manager. This is particularly
 331     useful for sending <literal>FDSTORE=1</literal> messages, as
 332     described above. The additional arguments are a pointer to the
 333     file descriptor array plus the number of file descriptors in the
 334     array. If the number of file descriptors is passed as 0, the call
 335     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 336     no file descriptors are passed. Note that sending file descriptors
 337     to the service manager on messages that do not expect them (i.e.
 338     without <literal>FDSTORE=1</literal>) they are immediately closed
 339     on reception.</para>
 340
 341     <para><function>sd_notify_barrier()</function> allows the caller to
 342     synchronize against reception of previously sent notification messages
 343     and uses the <literal>BARRIER=1</literal> command. It takes a relative
 344     <varname>timeout</varname> value in microseconds which is passed to
 345     <citerefentry><refentrytitle>ppoll</refentrytitle><manvolnum>2</manvolnum>
 346     </citerefentry>. A value of UINT64_MAX is interpreted as infinite timeout.
 347     </para>
 348   </refsect1>
 349
 350   <refsect1>
 351     <title>Return Value</title>
 352
 353     <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
 354     not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
 355     positive value. In order to support both service managers that implement this scheme and those which do not, it is
 356     generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
 357     the notification message was enqueued properly, it does not reflect whether the message could be processed
 358     successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
 359     <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
 360     above).</para>
 361   </refsect1>
 362
 363   <refsect1>
 364     <title>Notes</title>
 365
 366     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 367
 368     <para>These functions send a single datagram with the
 369     state string as payload to the <constant>AF_UNIX</constant> socket
 370     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 371     variable. If the first character of
 372     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 373     string is understood as Linux abstract namespace socket. The
 374     datagram is accompanied by the process credentials of the sending
 375     service, using SCM_CREDENTIALS.</para>
 376   </refsect1>
 377
 378   <refsect1>
 379     <title>Environment</title>
 380
 381     <variablelist class='environment-variables'>
 382       <varlistentry>
 383         <term><varname>$NOTIFY_SOCKET</varname></term>
 384
 385         <listitem><para>Set by the service manager for supervised
 386         processes for status and start-up completion notification.
 387         This environment variable specifies the socket
 388         <function>sd_notify()</function> talks to. See above for
 389         details.</para></listitem>
 390       </varlistentry>
 391     </variablelist>
 392   </refsect1>
 393
 394   <refsect1>
 395     <title>Examples</title>
 396
 397     <example>
 398       <title>Start-up Notification</title>
 399
 400       <para>When a service finished starting up, it might issue the
 401       following call to notify the service manager:</para>
 402
 403       <programlisting>sd_notify(0, "READY=1");</programlisting>
 404     </example>
 405
 406     <example>
 407       <title>Extended Start-up Notification</title>
 408
 409       <para>A service could send the following after completing
 410       initialization:</para>
 411
 412       <programlisting>sd_notifyf(0, "READY=1\n"
 413         "STATUS=Processing requests…\n"
 414         "MAINPID=%lu",
 415         (unsigned long) getpid());</programlisting>
 416     </example>
 417
 418     <example>
 419       <title>Error Cause Notification</title>
 420
 421       <para>A service could send the following shortly before exiting, on failure:</para>
 422
 423       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 424         "ERRNO=%i",
 425         strerror(errno),
 426         errno);</programlisting>
 427     </example>
 428
 429     <example>
 430       <title>Store a File Descriptor in the Service Manager</title>
 431
 432       <para>To store an open file descriptor in the service manager,
 433       in order to continue operation after a service restart without
 434       losing state, use <literal>FDSTORE=1</literal>:</para>
 435
 436       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 437     </example>
 438
 439     <example>
 440       <title>Eliminating race conditions</title>
 441
 442       <para>When the client sending the notifications is not spawned
 443       by the service manager, it may exit too quickly and the service
 444       manager may fail to attribute them correctly to the unit. To
 445       prevent such races, use <function>sd_notify_barrier()</function>
 446       to synchronize against reception of all notifications sent before
 447       this call is made.</para>
 448
 449       <programlisting>sd_notify(0, "READY=1");
 450       /* set timeout to 5 seconds */
 451       sd_notify_barrier(0, 5 * 1000000);
 452       </programlisting>
 453     </example>
 454   </refsect1>
 455
 456   <refsect1>
 457     <title>See Also</title>
 458     <para>
 459       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 460       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 461       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 462       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 463       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 464       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 465       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 466     </para>
 467   </refsect1>
 468
 469 </refentry>