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
 128         is finished. This is only used by systemd if the service
 129         definition file has Type=notify set. Since there is little
 130         value in signaling non-readiness, the only value services
 131         should send is <literal>READY=1</literal> (i.e.
 132         <literal>READY=0</literal> is not defined).</para></listitem>
 133       </varlistentry>
 134
 135       <varlistentry>
 136         <term>RELOADING=1</term>
 137
 138         <listitem><para>Tells the service manager that the service is
 139         reloading its configuration. This is useful to allow the
 140         service manager to track the service's internal state, and
 141         present it to the user. Note that a service that sends this
 142         notification must also send a <literal>READY=1</literal>
 143         notification when it completed reloading its
 144         configuration. Reloads are propagated in the same way as they
 145         are when initiated by the user.</para></listitem>
 146       </varlistentry>
 147
 148       <varlistentry>
 149         <term>STOPPING=1</term>
 150
 151         <listitem><para>Tells the service manager that the service is
 152         beginning its shutdown. This is useful to allow the service
 153         manager to track the service's internal state, and present it
 154         to the user.</para></listitem>
 155       </varlistentry>
 156
 157       <varlistentry>
 158         <term>STATUS=…</term>
 159
 160         <listitem><para>Passes a single-line UTF-8 status string back
 161         to the service manager that describes the service state. This
 162         is free-form and can be used for various purposes: general
 163         state feedback, fsck-like programs could pass completion
 164         percentages and failing programs could pass a human-readable
 165         error message. Example: <literal>STATUS=Completed 66% of file
 166         system check…</literal></para></listitem>
 167       </varlistentry>
 168
 169       <varlistentry>
 170         <term>ERRNO=…</term>
 171
 172         <listitem><para>If a service fails, the errno-style error
 173         code, formatted as string. Example: <literal>ERRNO=2</literal>
 174         for ENOENT.</para></listitem>
 175       </varlistentry>
 176
 177       <varlistentry>
 178         <term>BUSERROR=…</term>
 179
 180         <listitem><para>If a service fails, the D-Bus error-style
 181         error code. Example:
 182         <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 183       </varlistentry>
 184
 185       <varlistentry>
 186         <term>MAINPID=…</term>
 187
 188         <listitem><para>The main process ID (PID) of the service, in
 189         case the service manager did not fork off the process itself.
 190         Example: <literal>MAINPID=4711</literal></para></listitem>
 191       </varlistentry>
 192
 193       <varlistentry>
 194         <term>WATCHDOG=1</term>
 195
 196         <listitem><para>Tells the service manager to update the
 197         watchdog timestamp. This is the keep-alive ping that services
 198         need to issue in regular intervals if
 199         <varname>WatchdogSec=</varname> is enabled for it. See
 200         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 201         for information how to enable this functionality and
 202         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 203         for the details of how the service can check whether the
 204         watchdog is enabled. </para></listitem>
 205       </varlistentry>
 206
 207
 208       <varlistentry>
 209         <term>FDSTORE=1</term>
 210
 211         <listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
 212         be maintained per-service by the service manager and will later be handed back using the usual file descriptor
 213         passing logic at the next invocation of the service, see
 214         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.  This is
 215         useful for implementing services that can restart after an explicit request or a crash without losing
 216         state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
 217         this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
 218         in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
 219         file descriptor. Note that the service manager will accept messages for a service only if its
 220         <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
 221         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If file
 222         descriptors sent are pollable (see
 223         <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
 224         <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
 225         automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
 226         which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
 227         object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
 228         to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
 229       </varlistentry>
 230
 231       <varlistentry>
 232         <term>FDNAME=…</term>
 233
 234         <listitem><para>When used in combination with
 235         <varname>FDSTORE=1</varname>, specifies a name for the
 236         submitted file descriptors. This name is passed to the service
 237         during activation, and may be queried using
 238         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 239         descriptors submitted without this field set, will implicitly
 240         get the name <literal>stored</literal> assigned. Note that, if
 241         multiple file descriptors are submitted at once, the specified
 242         name will be assigned to all of them. In order to assign
 243         different names to submitted file descriptors, submit them in
 244         separate invocations of
 245         <function>sd_pid_notify_with_fds()</function>. The name may
 246         consist of any ASCII character, but must not contain control
 247         characters or <literal>:</literal>. It may not be longer than
 248         255 characters. If a submitted name does not follow these
 249         restrictions, it is ignored.</para></listitem>
 250       </varlistentry>
 251
 252       <varlistentry>
 253         <term>WATCHDOG_USEC=…</term>
 254
 255         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 256         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 257         or <function>sd_watchdog_enabled()</function>.
 258         Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
 259       </varlistentry>
 260
 261     </variablelist>
 262
 263     <para>It is recommended to prefix variable names that are not
 264     listed above with <varname>X_</varname> to avoid namespace
 265     clashes.</para>
 266
 267     <para>Note that systemd will accept status data sent from a
 268     service only if the <varname>NotifyAccess=</varname> option is
 269     correctly set in the service definition file. See
 270     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 271     for details.</para>
 272
 273     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
 274     the sending process is still around at the time PID 1 processes the message, or if the sending process is
 275     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
 276     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
 277     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
 278     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
 279     attribute the message to the unit, and thus will ignore it, even if
 280     <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
 281
 282     <para><function>sd_notifyf()</function> is similar to
 283     <function>sd_notify()</function> but takes a
 284     <function>printf()</function>-like format string plus
 285     arguments.</para>
 286
 287     <para><function>sd_pid_notify()</function> and
 288     <function>sd_pid_notifyf()</function> are similar to
 289     <function>sd_notify()</function> and
 290     <function>sd_notifyf()</function> but take a process ID (PID) to
 291     use as originating PID for the message as first argument. This is
 292     useful to send notification messages on behalf of other processes,
 293     provided the appropriate privileges are available. If the PID
 294     argument is specified as 0, the process ID of the calling process
 295     is used, in which case the calls are fully equivalent to
 296     <function>sd_notify()</function> and
 297     <function>sd_notifyf()</function>.</para>
 298
 299     <para><function>sd_pid_notify_with_fds()</function> is similar to
 300     <function>sd_pid_notify()</function> but takes an additional array
 301     of file descriptors. These file descriptors are sent along the
 302     notification message to the service manager. This is particularly
 303     useful for sending <literal>FDSTORE=1</literal> messages, as
 304     described above. The additional arguments are a pointer to the
 305     file descriptor array plus the number of file descriptors in the
 306     array. If the number of file descriptors is passed as 0, the call
 307     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 308     no file descriptors are passed. Note that sending file descriptors
 309     to the service manager on messages that do not expect them (i.e.
 310     without <literal>FDSTORE=1</literal>) they are immediately closed
 311     on reception.</para>
 312   </refsect1>
 313
 314   <refsect1>
 315     <title>Return Value</title>
 316
 317     <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
 318     not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
 319     positive value. In order to support both service managers that implement this scheme and those which do not, it is
 320     generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
 321     the notification message was enqueued properly, it does not reflect whether the message could be processed
 322     successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
 323     <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
 324     above).</para>
 325   </refsect1>
 326
 327   <refsect1>
 328     <title>Notes</title>
 329
 330     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 331
 332     <para>These functions send a single datagram with the
 333     state string as payload to the <constant>AF_UNIX</constant> socket
 334     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 335     variable. If the first character of
 336     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 337     string is understood as Linux abstract namespace socket. The
 338     datagram is accompanied by the process credentials of the sending
 339     service, using SCM_CREDENTIALS.</para>
 340   </refsect1>
 341
 342   <refsect1>
 343     <title>Environment</title>
 344
 345     <variablelist class='environment-variables'>
 346       <varlistentry>
 347         <term><varname>$NOTIFY_SOCKET</varname></term>
 348
 349         <listitem><para>Set by the service manager for supervised
 350         processes for status and start-up completion notification.
 351         This environment variable specifies the socket
 352         <function>sd_notify()</function> talks to. See above for
 353         details.</para></listitem>
 354       </varlistentry>
 355     </variablelist>
 356   </refsect1>
 357
 358   <refsect1>
 359     <title>Examples</title>
 360
 361     <example>
 362       <title>Start-up Notification</title>
 363
 364       <para>When a service finished starting up, it might issue the
 365       following call to notify the service manager:</para>
 366
 367       <programlisting>sd_notify(0, "READY=1");</programlisting>
 368     </example>
 369
 370     <example>
 371       <title>Extended Start-up Notification</title>
 372
 373       <para>A service could send the following after completing
 374       initialization:</para>
 375
 376       <programlisting>sd_notifyf(0, "READY=1\n"
 377         "STATUS=Processing requests…\n"
 378         "MAINPID=%lu",
 379         (unsigned long) getpid());</programlisting>
 380     </example>
 381
 382     <example>
 383       <title>Error Cause Notification</title>
 384
 385       <para>A service could send the following shortly before exiting, on failure:</para>
 386
 387       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 388         "ERRNO=%i",
 389         strerror(errno),
 390         errno);</programlisting>
 391     </example>
 392
 393     <example>
 394       <title>Store a File Descriptor in the Service Manager</title>
 395
 396       <para>To store an open file descriptor in the service manager,
 397       in order to continue operation after a service restart without
 398       losing state, use <literal>FDSTORE=1</literal>:</para>
 399
 400       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 401     </example>
 402   </refsect1>
 403
 404   <refsect1>
 405     <title>See Also</title>
 406     <para>
 407       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 408       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 409       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 410       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 411       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 412       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 413       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 414     </para>
 415   </refsect1>
 416
 417 </refentry>