man/sd_notify.xml

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  10   Copyright 2010 Lennart Poettering
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  25
  26 <refentry id="sd_notify"
  27   xmlns:xi="http://www.w3.org/2001/XInclude">
  28
  29   <refentryinfo>
  30     <title>sd_notify</title>
  31     <productname>systemd</productname>
  32
  33     <authorgroup>
  34       <author>
  35         <contrib>Developer</contrib>
  36         <firstname>Lennart</firstname>
  37         <surname>Poettering</surname>
  38         <email>lennart@poettering.net</email>
  39       </author>
  40     </authorgroup>
  41   </refentryinfo>
  42
  43   <refmeta>
  44     <refentrytitle>sd_notify</refentrytitle>
  45     <manvolnum>3</manvolnum>
  46   </refmeta>
  47
  48   <refnamediv>
  49     <refname>sd_notify</refname>
  50     <refname>sd_notifyf</refname>
  51     <refname>sd_pid_notify</refname>
  52     <refname>sd_pid_notifyf</refname>
  53     <refname>sd_pid_notify_with_fds</refname>
  54     <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
  55   </refnamediv>
  56
  57   <refsynopsisdiv>
  58     <funcsynopsis>
  59       <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  60
  61       <funcprototype>
  62         <funcdef>int <function>sd_notify</function></funcdef>
  63         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  64         <paramdef>const char *<parameter>state</parameter></paramdef>
  65       </funcprototype>
  66
  67       <funcprototype>
  68         <funcdef>int <function>sd_notifyf</function></funcdef>
  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</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       </funcprototype>
  80
  81       <funcprototype>
  82         <funcdef>int <function>sd_pid_notifyf</function></funcdef>
  83         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  84         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  85         <paramdef>const char *<parameter>format</parameter></paramdef>
  86         <paramdef>…</paramdef>
  87       </funcprototype>
  88
  89       <funcprototype>
  90         <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
  91         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  92         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  93         <paramdef>const char *<parameter>state</parameter></paramdef>
  94         <paramdef>const int *<parameter>fds</parameter></paramdef>
  95         <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
  96       </funcprototype>
  97     </funcsynopsis>
  98   </refsynopsisdiv>
  99
 100   <refsect1>
 101     <title>Description</title>
 102     <para><function>sd_notify()</function> may be called by a service
 103     to notify the service manager about state changes. It can be used
 104     to send arbitrary information, encoded in an
 105     environment-block-like string. Most importantly, it can be used for
 106     start-up completion notification.</para>
 107
 108     <para>If the <parameter>unset_environment</parameter> parameter is
 109     non-zero, <function>sd_notify()</function> will unset the
 110     <varname>$NOTIFY_SOCKET</varname> environment variable before
 111     returning (regardless of whether the function call itself
 112     succeeded or not). Further calls to
 113     <function>sd_notify()</function> will then fail, but the variable
 114     is no longer inherited by child processes.</para>
 115
 116     <para>The <parameter>state</parameter> parameter should contain a
 117     newline-separated list of variable assignments, similar in style
 118     to an environment block. A trailing newline is implied if none is
 119     specified. The string may contain any kind of variable
 120     assignments, but the following shall be considered
 121     well-known:</para>
 122
 123     <variablelist>
 124       <varlistentry>
 125         <term>READY=1</term>
 126
 127         <listitem><para>Tells the service manager that service startup is finished, or the service finished loading its
 128         configuration. This is only used by systemd if the service definition file has <varname>Type=notify</varname>
 129         set. Since there is little value in signaling non-readiness, the only value services should send is
 130         <literal>READY=1</literal> (i.e.  <literal>READY=0</literal> is not defined).</para></listitem>
 131       </varlistentry>
 132
 133       <varlistentry>
 134         <term>RELOADING=1</term>
 135
 136         <listitem><para>Tells the service manager that the service is
 137         reloading its configuration. This is useful to allow the
 138         service manager to track the service's internal state, and
 139         present it to the user. Note that a service that sends this
 140         notification must also send a <literal>READY=1</literal>
 141         notification when it completed reloading its
 142         configuration. Reloads are propagated in the same way as they
 143         are when initiated by the user.</para></listitem>
 144       </varlistentry>
 145
 146       <varlistentry>
 147         <term>STOPPING=1</term>
 148
 149         <listitem><para>Tells the service manager that the service is
 150         beginning its shutdown. This is useful to allow the service
 151         manager to track the service's internal state, and present it
 152         to the user.</para></listitem>
 153       </varlistentry>
 154
 155       <varlistentry>
 156         <term>STATUS=…</term>
 157
 158         <listitem><para>Passes a single-line UTF-8 status string back
 159         to the service manager that describes the service state. This
 160         is free-form and can be used for various purposes: general
 161         state feedback, fsck-like programs could pass completion
 162         percentages and failing programs could pass a human-readable
 163         error message. Example: <literal>STATUS=Completed 66% of file
 164         system check…</literal></para></listitem>
 165       </varlistentry>
 166
 167       <varlistentry>
 168         <term>ERRNO=…</term>
 169
 170         <listitem><para>If a service fails, the errno-style error
 171         code, formatted as string. Example: <literal>ERRNO=2</literal>
 172         for ENOENT.</para></listitem>
 173       </varlistentry>
 174
 175       <varlistentry>
 176         <term>BUSERROR=…</term>
 177
 178         <listitem><para>If a service fails, the D-Bus error-style
 179         error code. Example:
 180         <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 181       </varlistentry>
 182
 183       <varlistentry>
 184         <term>MAINPID=…</term>
 185
 186         <listitem><para>The main process ID (PID) of the service, in
 187         case the service manager did not fork off the process itself.
 188         Example: <literal>MAINPID=4711</literal></para></listitem>
 189       </varlistentry>
 190
 191       <varlistentry>
 192         <term>WATCHDOG=1</term>
 193
 194         <listitem><para>Tells the service manager to update the
 195         watchdog timestamp. This is the keep-alive ping that services
 196         need to issue in regular intervals if
 197         <varname>WatchdogSec=</varname> is enabled for it. See
 198         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 199         for information how to enable this functionality and
 200         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 201         for the details of how the service can check whether the
 202         watchdog is enabled. </para></listitem>
 203       </varlistentry>
 204
 205       <varlistentry>
 206         <term>WATCHDOG_USEC=…</term>
 207
 208         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 209         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 210         or <function>sd_watchdog_enabled()</function>.
 211         Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
 212       </varlistentry>
 213
 214       <varlistentry>
 215         <term>FDSTORE=1</term>
 216
 217         <listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
 218         be maintained per-service by the service manager and will later be handed back using the usual file descriptor
 219         passing logic at the next invocation of the service, see
 220         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.  This is
 221         useful for implementing services that can restart after an explicit request or a crash without losing
 222         state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
 223         this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
 224         in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
 225         file descriptor. Note that the service manager will accept messages for a service only if its
 226         <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
 227         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If file
 228         descriptors sent are pollable (see
 229         <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
 230         <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
 231         automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
 232         which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
 233         object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
 234         to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
 235       </varlistentry>
 236
 237       <varlistentry>
 238         <term>FDSTOREREMOVE=1</term>
 239
 240         <listitem><para>Removes file descriptors from the file descriptor store. This field needs to be combined with
 241         <varname>FDNAME=</varname> to specify the name of the file descriptors to remove.</para></listitem>
 242       </varlistentry>
 243
 244       <varlistentry>
 245         <term>FDNAME=…</term>
 246
 247         <listitem><para>When used in combination with <varname>FDSTORE=1</varname>, specifies a name for the submitted
 248         file descriptors. When used with <varname>FDSTOREREMOVE=1</varname>, specifies the name for the file
 249         descriptors to remove. This name is passed to the service during activation, and may be queried using
 250         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 251         descriptors submitted without this field set, will implicitly get the name <literal>stored</literal>
 252         assigned. Note that, if multiple file descriptors are submitted at once, the specified name will be assigned to
 253         all of them. In order to assign different names to submitted file descriptors, submit them in separate
 254         invocations of <function>sd_pid_notify_with_fds()</function>. The name may consist of arbitrary ASCII
 255         characters except control characters or <literal>:</literal>. It may not be longer than 255 characters. If a
 256         submitted name does not follow these restrictions, it is ignored.</para></listitem>
 257       </varlistentry>
 258
 259     </variablelist>
 260
 261     <para>It is recommended to prefix variable names that are not
 262     listed above with <varname>X_</varname> to avoid namespace
 263     clashes.</para>
 264
 265     <para>Note that systemd will accept status data sent from a
 266     service only if the <varname>NotifyAccess=</varname> option is
 267     correctly set in the service definition file. See
 268     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 269     for details.</para>
 270
 271     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
 272     the sending process is still around at the time PID 1 processes the message, or if the sending process is
 273     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
 274     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
 275     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
 276     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
 277     attribute the message to the unit, and thus will ignore it, even if
 278     <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
 279
 280     <para><function>sd_notifyf()</function> is similar to
 281     <function>sd_notify()</function> but takes a
 282     <function>printf()</function>-like format string plus
 283     arguments.</para>
 284
 285     <para><function>sd_pid_notify()</function> and
 286     <function>sd_pid_notifyf()</function> are similar to
 287     <function>sd_notify()</function> and
 288     <function>sd_notifyf()</function> but take a process ID (PID) to
 289     use as originating PID for the message as first argument. This is
 290     useful to send notification messages on behalf of other processes,
 291     provided the appropriate privileges are available. If the PID
 292     argument is specified as 0, the process ID of the calling process
 293     is used, in which case the calls are fully equivalent to
 294     <function>sd_notify()</function> and
 295     <function>sd_notifyf()</function>.</para>
 296
 297     <para><function>sd_pid_notify_with_fds()</function> is similar to
 298     <function>sd_pid_notify()</function> but takes an additional array
 299     of file descriptors. These file descriptors are sent along the
 300     notification message to the service manager. This is particularly
 301     useful for sending <literal>FDSTORE=1</literal> messages, as
 302     described above. The additional arguments are a pointer to the
 303     file descriptor array plus the number of file descriptors in the
 304     array. If the number of file descriptors is passed as 0, the call
 305     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 306     no file descriptors are passed. Note that sending file descriptors
 307     to the service manager on messages that do not expect them (i.e.
 308     without <literal>FDSTORE=1</literal>) they are immediately closed
 309     on reception.</para>
 310   </refsect1>
 311
 312   <refsect1>
 313     <title>Return Value</title>
 314
 315     <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
 316     not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
 317     positive value. In order to support both service managers that implement this scheme and those which do not, it is
 318     generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
 319     the notification message was enqueued properly, it does not reflect whether the message could be processed
 320     successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
 321     <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
 322     above).</para>
 323   </refsect1>
 324
 325   <refsect1>
 326     <title>Notes</title>
 327
 328     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 329
 330     <para>These functions send a single datagram with the
 331     state string as payload to the <constant>AF_UNIX</constant> socket
 332     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 333     variable. If the first character of
 334     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 335     string is understood as Linux abstract namespace socket. The
 336     datagram is accompanied by the process credentials of the sending
 337     service, using SCM_CREDENTIALS.</para>
 338   </refsect1>
 339
 340   <refsect1>
 341     <title>Environment</title>
 342
 343     <variablelist class='environment-variables'>
 344       <varlistentry>
 345         <term><varname>$NOTIFY_SOCKET</varname></term>
 346
 347         <listitem><para>Set by the service manager for supervised
 348         processes for status and start-up completion notification.
 349         This environment variable specifies the socket
 350         <function>sd_notify()</function> talks to. See above for
 351         details.</para></listitem>
 352       </varlistentry>
 353     </variablelist>
 354   </refsect1>
 355
 356   <refsect1>
 357     <title>Examples</title>
 358
 359     <example>
 360       <title>Start-up Notification</title>
 361
 362       <para>When a service finished starting up, it might issue the
 363       following call to notify the service manager:</para>
 364
 365       <programlisting>sd_notify(0, "READY=1");</programlisting>
 366     </example>
 367
 368     <example>
 369       <title>Extended Start-up Notification</title>
 370
 371       <para>A service could send the following after completing
 372       initialization:</para>
 373
 374       <programlisting>sd_notifyf(0, "READY=1\n"
 375         "STATUS=Processing requests…\n"
 376         "MAINPID=%lu",
 377         (unsigned long) getpid());</programlisting>
 378     </example>
 379
 380     <example>
 381       <title>Error Cause Notification</title>
 382
 383       <para>A service could send the following shortly before exiting, on failure:</para>
 384
 385       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 386         "ERRNO=%i",
 387         strerror(errno),
 388         errno);</programlisting>
 389     </example>
 390
 391     <example>
 392       <title>Store a File Descriptor in the Service Manager</title>
 393
 394       <para>To store an open file descriptor in the service manager,
 395       in order to continue operation after a service restart without
 396       losing state, use <literal>FDSTORE=1</literal>:</para>
 397
 398       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 399     </example>
 400   </refsect1>
 401
 402   <refsect1>
 403     <title>See Also</title>
 404     <para>
 405       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 406       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 407       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 408       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 409       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 410       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 411       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 412     </para>
 413   </refsect1>
 414
 415 </refentry>