man/sd_notify.xml

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   5 <!--
   6   SPDX-License-Identifier: LGPL-2.1+
   7
   8   Copyright 2010 Lennart Poettering
   9 -->
  10
  11 <refentry id="sd_notify"
  12   xmlns:xi="http://www.w3.org/2001/XInclude">
  13
  14   <refentryinfo>
  15     <title>sd_notify</title>
  16     <productname>systemd</productname>
  17
  18     <authorgroup>
  19       <author>
  20         <contrib>Developer</contrib>
  21         <firstname>Lennart</firstname>
  22         <surname>Poettering</surname>
  23         <email>lennart@poettering.net</email>
  24       </author>
  25     </authorgroup>
  26   </refentryinfo>
  27
  28   <refmeta>
  29     <refentrytitle>sd_notify</refentrytitle>
  30     <manvolnum>3</manvolnum>
  31   </refmeta>
  32
  33   <refnamediv>
  34     <refname>sd_notify</refname>
  35     <refname>sd_notifyf</refname>
  36     <refname>sd_pid_notify</refname>
  37     <refname>sd_pid_notifyf</refname>
  38     <refname>sd_pid_notify_with_fds</refname>
  39     <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
  40   </refnamediv>
  41
  42   <refsynopsisdiv>
  43     <funcsynopsis>
  44       <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  45
  46       <funcprototype>
  47         <funcdef>int <function>sd_notify</function></funcdef>
  48         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  49         <paramdef>const char *<parameter>state</parameter></paramdef>
  50       </funcprototype>
  51
  52       <funcprototype>
  53         <funcdef>int <function>sd_notifyf</function></funcdef>
  54         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  55         <paramdef>const char *<parameter>format</parameter></paramdef>
  56         <paramdef>…</paramdef>
  57       </funcprototype>
  58
  59       <funcprototype>
  60         <funcdef>int <function>sd_pid_notify</function></funcdef>
  61         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  62         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  63         <paramdef>const char *<parameter>state</parameter></paramdef>
  64       </funcprototype>
  65
  66       <funcprototype>
  67         <funcdef>int <function>sd_pid_notifyf</function></funcdef>
  68         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  69         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  70         <paramdef>const char *<parameter>format</parameter></paramdef>
  71         <paramdef>…</paramdef>
  72       </funcprototype>
  73
  74       <funcprototype>
  75         <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
  76         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  77         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  78         <paramdef>const char *<parameter>state</parameter></paramdef>
  79         <paramdef>const int *<parameter>fds</parameter></paramdef>
  80         <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
  81       </funcprototype>
  82     </funcsynopsis>
  83   </refsynopsisdiv>
  84
  85   <refsect1>
  86     <title>Description</title>
  87     <para><function>sd_notify()</function> may be called by a service
  88     to notify the service manager about state changes. It can be used
  89     to send arbitrary information, encoded in an
  90     environment-block-like string. Most importantly, it can be used for
  91     start-up completion notification.</para>
  92
  93     <para>If the <parameter>unset_environment</parameter> parameter is
  94     non-zero, <function>sd_notify()</function> will unset the
  95     <varname>$NOTIFY_SOCKET</varname> environment variable before
  96     returning (regardless of whether the function call itself
  97     succeeded or not). Further calls to
  98     <function>sd_notify()</function> will then fail, but the variable
  99     is no longer inherited by child processes.</para>
 100
 101     <para>The <parameter>state</parameter> parameter should contain a
 102     newline-separated list of variable assignments, similar in style
 103     to an environment block. A trailing newline is implied if none is
 104     specified. The string may contain any kind of variable
 105     assignments, but the following shall be considered
 106     well-known:</para>
 107
 108     <variablelist>
 109       <varlistentry>
 110         <term>READY=1</term>
 111
 112         <listitem><para>Tells the service manager that service startup is finished, or the service finished loading its
 113         configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
 114         set. Since there is little value in signaling non-readiness, the only value services should send is
 115         <literal>READY=1</literal> (i.e.  <literal>READY=0</literal> is not defined).</para></listitem>
 116       </varlistentry>
 117
 118       <varlistentry>
 119         <term>RELOADING=1</term>
 120
 121         <listitem><para>Tells the service manager that the service is
 122         reloading its configuration. This is useful to allow the
 123         service manager to track the service's internal state, and
 124         present it to the user. Note that a service that sends this
 125         notification must also send a <literal>READY=1</literal>
 126         notification when it completed reloading its
 127         configuration. Reloads are propagated in the same way as they
 128         are when initiated by the user.</para></listitem>
 129       </varlistentry>
 130
 131       <varlistentry>
 132         <term>STOPPING=1</term>
 133
 134         <listitem><para>Tells the service manager that the service is
 135         beginning its shutdown. This is useful to allow the service
 136         manager to track the service's internal state, and present it
 137         to the user.</para></listitem>
 138       </varlistentry>
 139
 140       <varlistentry>
 141         <term>STATUS=…</term>
 142
 143         <listitem><para>Passes a single-line UTF-8 status string back
 144         to the service manager that describes the service state. This
 145         is free-form and can be used for various purposes: general
 146         state feedback, fsck-like programs could pass completion
 147         percentages and failing programs could pass a human-readable
 148         error message. Example: <literal>STATUS=Completed 66% of file
 149         system check…</literal></para></listitem>
 150       </varlistentry>
 151
 152       <varlistentry>
 153         <term>ERRNO=…</term>
 154
 155         <listitem><para>If a service fails, the errno-style error
 156         code, formatted as string. Example: <literal>ERRNO=2</literal>
 157         for ENOENT.</para></listitem>
 158       </varlistentry>
 159
 160       <varlistentry>
 161         <term>BUSERROR=…</term>
 162
 163         <listitem><para>If a service fails, the D-Bus error-style
 164         error code. Example:
 165         <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 166       </varlistentry>
 167
 168       <varlistentry>
 169         <term>MAINPID=…</term>
 170
 171         <listitem><para>The main process ID (PID) of the service, in
 172         case the service manager did not fork off the process itself.
 173         Example: <literal>MAINPID=4711</literal></para></listitem>
 174       </varlistentry>
 175
 176       <varlistentry>
 177         <term>WATCHDOG=1</term>
 178
 179         <listitem><para>Tells the service manager to update the
 180         watchdog timestamp. This is the keep-alive ping that services
 181         need to issue in regular intervals if
 182         <varname>WatchdogSec=</varname> is enabled for it. See
 183         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 184         for information how to enable this functionality and
 185         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 186         for the details of how the service can check whether the
 187         watchdog is enabled. </para></listitem>
 188       </varlistentry>
 189
 190       <varlistentry>
 191         <term>WATCHDOG_USEC=…</term>
 192
 193         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 194         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 195         or <function>sd_watchdog_enabled()</function>.
 196         Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
 197       </varlistentry>
 198
 199       <varlistentry>
 200         <term>EXTEND_TIMEOUT_USEC=…</term>
 201
 202         <listitem><para>Tells the service manager to extend the startup, runtime or shutdown service timeout
 203         corresponding the current state. The value specified is a time in microseconds during which the service must
 204         send a new message. A service timeout will occur if the message isn't received, but only if the runtime of the
 205         current state is beyond the original maximium times of <varname>TimeoutStartSec=</varname>, <varname>RuntimeMaxSec=</varname>,
 206         and <varname>TimeoutStopSec=</varname>.
 207         See <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 208         for effects on the service timeouts.</para></listitem>
 209       </varlistentry>
 210
 211       <varlistentry>
 212         <term>FDSTORE=1</term>
 213
 214         <listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
 215         be maintained per-service by the service manager and will later be handed back using the usual file descriptor
 216         passing logic at the next invocation of the service, see
 217         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.  This is
 218         useful for implementing services that can restart after an explicit request or a crash without losing
 219         state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
 220         this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
 221         in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
 222         file descriptor. Note that the service manager will accept messages for a service only if its
 223         <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
 224         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If file
 225         descriptors sent are pollable (see
 226         <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
 227         <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
 228         automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
 229         which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
 230         object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
 231         to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
 232       </varlistentry>
 233
 234       <varlistentry>
 235         <term>FDSTOREREMOVE=1</term>
 236
 237         <listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
 238         <varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem>
 239       </varlistentry>
 240
 241       <varlistentry>
 242         <term>FDNAME=…</term>
 243
 244         <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
 245         file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
 246         descriptors to remove. This name is passed to the service during activation, and may be queried using
 247         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 248         descriptors submitted without this field set, will implicitly get the name <literal>stored</literal>
 249         assigned. Note that, if multiple file descriptors are submitted at once, the specified name will be assigned to
 250         all of them. In order to assign different names to submitted file descriptors, submit them in separate
 251         invocations of <function>sd_pid_notify_with_fds()</function>. The name may consist of arbitrary ASCII
 252         characters except control characters or <literal>:</literal>. It may not be longer than 255 characters. If a
 253         submitted name does not follow these restrictions, it is ignored.</para></listitem>
 254       </varlistentry>
 255
 256     </variablelist>
 257
 258     <para>It is recommended to prefix variable names that are not
 259     listed above with <varname>X_</varname> to avoid namespace
 260     clashes.</para>
 261
 262     <para>Note that systemd will accept status data sent from a
 263     service only if the <varname>NotifyAccess=</varname> option is
 264     correctly set in the service definition file. See
 265     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 266     for details.</para>
 267
 268     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
 269     the sending process is still around at the time PID 1 processes the message, or if the sending process is
 270     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
 271     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
 272     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
 273     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
 274     attribute the message to the unit, and thus will ignore it, even if
 275     <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
 276
 277     <para><function>sd_notifyf()</function> is similar to
 278     <function>sd_notify()</function> but takes a
 279     <function>printf()</function>-like format string plus
 280     arguments.</para>
 281
 282     <para><function>sd_pid_notify()</function> and
 283     <function>sd_pid_notifyf()</function> are similar to
 284     <function>sd_notify()</function> and
 285     <function>sd_notifyf()</function> but take a process ID (PID) to
 286     use as originating PID for the message as first argument. This is
 287     useful to send notification messages on behalf of other processes,
 288     provided the appropriate privileges are available. If the PID
 289     argument is specified as 0, the process ID of the calling process
 290     is used, in which case the calls are fully equivalent to
 291     <function>sd_notify()</function> and
 292     <function>sd_notifyf()</function>.</para>
 293
 294     <para><function>sd_pid_notify_with_fds()</function> is similar to
 295     <function>sd_pid_notify()</function> but takes an additional array
 296     of file descriptors. These file descriptors are sent along the
 297     notification message to the service manager. This is particularly
 298     useful for sending <literal>FDSTORE=1</literal> messages, as
 299     described above. The additional arguments are a pointer to the
 300     file descriptor array plus the number of file descriptors in the
 301     array. If the number of file descriptors is passed as 0, the call
 302     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 303     no file descriptors are passed. Note that sending file descriptors
 304     to the service manager on messages that do not expect them (i.e.
 305     without <literal>FDSTORE=1</literal>) they are immediately closed
 306     on reception.</para>
 307   </refsect1>
 308
 309   <refsect1>
 310     <title>Return Value</title>
 311
 312     <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
 313     not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
 314     positive value. In order to support both service managers that implement this scheme and those which do not, it is
 315     generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
 316     the notification message was enqueued properly, it does not reflect whether the message could be processed
 317     successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
 318     <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
 319     above).</para>
 320   </refsect1>
 321
 322   <refsect1>
 323     <title>Notes</title>
 324
 325     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 326
 327     <para>These functions send a single datagram with the
 328     state string as payload to the <constant>AF_UNIX</constant> socket
 329     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 330     variable. If the first character of
 331     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 332     string is understood as Linux abstract namespace socket. The
 333     datagram is accompanied by the process credentials of the sending
 334     service, using SCM_CREDENTIALS.</para>
 335   </refsect1>
 336
 337   <refsect1>
 338     <title>Environment</title>
 339
 340     <variablelist class='environment-variables'>
 341       <varlistentry>
 342         <term><varname>$NOTIFY_SOCKET</varname></term>
 343
 344         <listitem><para>Set by the service manager for supervised
 345         processes for status and start-up completion notification.
 346         This environment variable specifies the socket
 347         <function>sd_notify()</function> talks to. See above for
 348         details.</para></listitem>
 349       </varlistentry>
 350     </variablelist>
 351   </refsect1>
 352
 353   <refsect1>
 354     <title>Examples</title>
 355
 356     <example>
 357       <title>Start-up Notification</title>
 358
 359       <para>When a service finished starting up, it might issue the
 360       following call to notify the service manager:</para>
 361
 362       <programlisting>sd_notify(0, "READY=1");</programlisting>
 363     </example>
 364
 365     <example>
 366       <title>Extended Start-up Notification</title>
 367
 368       <para>A service could send the following after completing
 369       initialization:</para>
 370
 371       <programlisting>sd_notifyf(0, "READY=1\n"
 372         "STATUS=Processing requests…\n"
 373         "MAINPID=%lu",
 374         (unsigned long) getpid());</programlisting>
 375     </example>
 376
 377     <example>
 378       <title>Error Cause Notification</title>
 379
 380       <para>A service could send the following shortly before exiting, on failure:</para>
 381
 382       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 383         "ERRNO=%i",
 384         strerror(errno),
 385         errno);</programlisting>
 386     </example>
 387
 388     <example>
 389       <title>Store a File Descriptor in the Service Manager</title>
 390
 391       <para>To store an open file descriptor in the service manager,
 392       in order to continue operation after a service restart without
 393       losing state, use <literal>FDSTORE=1</literal>:</para>
 394
 395       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 396     </example>
 397   </refsect1>
 398
 399   <refsect1>
 400     <title>See Also</title>
 401     <para>
 402       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 403       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 404       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 405       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 406       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 407       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 408       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 409     </para>
 410   </refsect1>
 411
 412 </refentry>