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       <varlistentry>
 208         <term>WATCHDOG_USEC=…</term>
 209
 210         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 211         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 212         or <function>sd_watchdog_enabled()</function>.
 213         Example : <literal>WATCHDOG_USEC=20000000</literal></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 file
 230         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>FDNAME=…</term>
 241
 242         <listitem><para>When used in combination with
 243         <varname>FDSTORE=1</varname>, specifies a name for the
 244         submitted file descriptors. This name is passed to the service
 245         during activation, and may be queried using
 246         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 247         descriptors submitted without this field set, will implicitly
 248         get the name <literal>stored</literal> assigned. Note that, if
 249         multiple file descriptors are submitted at once, the specified
 250         name will be assigned to all of them. In order to assign
 251         different names to submitted file descriptors, submit them in
 252         separate invocations of
 253         <function>sd_pid_notify_with_fds()</function>. The name may
 254         consist of any ASCII character, but must not contain control
 255         characters or <literal>:</literal>. It may not be longer than
 256         255 characters. If a submitted name does not follow these
 257         restrictions, it is ignored.</para></listitem>
 258       </varlistentry>
 259
 260     </variablelist>
 261
 262     <para>It is recommended to prefix variable names that are not
 263     listed above with <varname>X_</varname> to avoid namespace
 264     clashes.</para>
 265
 266     <para>Note that systemd will accept status data sent from a
 267     service only if the <varname>NotifyAccess=</varname> option is
 268     correctly set in the service definition file. See
 269     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 270     for details.</para>
 271
 272     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
 273     the sending process is still around at the time PID 1 processes the message, or if the sending process is
 274     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
 275     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
 276     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
 277     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
 278     attribute the message to the unit, and thus will ignore it, even if
 279     <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
 280
 281     <para><function>sd_notifyf()</function> is similar to
 282     <function>sd_notify()</function> but takes a
 283     <function>printf()</function>-like format string plus
 284     arguments.</para>
 285
 286     <para><function>sd_pid_notify()</function> and
 287     <function>sd_pid_notifyf()</function> are similar to
 288     <function>sd_notify()</function> and
 289     <function>sd_notifyf()</function> but take a process ID (PID) to
 290     use as originating PID for the message as first argument. This is
 291     useful to send notification messages on behalf of other processes,
 292     provided the appropriate privileges are available. If the PID
 293     argument is specified as 0, the process ID of the calling process
 294     is used, in which case the calls are fully equivalent to
 295     <function>sd_notify()</function> and
 296     <function>sd_notifyf()</function>.</para>
 297
 298     <para><function>sd_pid_notify_with_fds()</function> is similar to
 299     <function>sd_pid_notify()</function> but takes an additional array
 300     of file descriptors. These file descriptors are sent along the
 301     notification message to the service manager. This is particularly
 302     useful for sending <literal>FDSTORE=1</literal> messages, as
 303     described above. The additional arguments are a pointer to the
 304     file descriptor array plus the number of file descriptors in the
 305     array. If the number of file descriptors is passed as 0, the call
 306     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 307     no file descriptors are passed. Note that sending file descriptors
 308     to the service manager on messages that do not expect them (i.e.
 309     without <literal>FDSTORE=1</literal>) they are immediately closed
 310     on reception.</para>
 311   </refsect1>
 312
 313   <refsect1>
 314     <title>Return Value</title>
 315
 316     <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
 317     not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
 318     positive value. In order to support both service managers that implement this scheme and those which do not, it is
 319     generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
 320     the notification message was enqueued properly, it does not reflect whether the message could be processed
 321     successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
 322     <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
 323     above).</para>
 324   </refsect1>
 325
 326   <refsect1>
 327     <title>Notes</title>
 328
 329     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 330
 331     <para>These functions send a single datagram with the
 332     state string as payload to the <constant>AF_UNIX</constant> socket
 333     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 334     variable. If the first character of
 335     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 336     string is understood as Linux abstract namespace socket. The
 337     datagram is accompanied by the process credentials of the sending
 338     service, using SCM_CREDENTIALS.</para>
 339   </refsect1>
 340
 341   <refsect1>
 342     <title>Environment</title>
 343
 344     <variablelist class='environment-variables'>
 345       <varlistentry>
 346         <term><varname>$NOTIFY_SOCKET</varname></term>
 347
 348         <listitem><para>Set by the service manager for supervised
 349         processes for status and start-up completion notification.
 350         This environment variable specifies the socket
 351         <function>sd_notify()</function> talks to. See above for
 352         details.</para></listitem>
 353       </varlistentry>
 354     </variablelist>
 355   </refsect1>
 356
 357   <refsect1>
 358     <title>Examples</title>
 359
 360     <example>
 361       <title>Start-up Notification</title>
 362
 363       <para>When a service finished starting up, it might issue the
 364       following call to notify the service manager:</para>
 365
 366       <programlisting>sd_notify(0, "READY=1");</programlisting>
 367     </example>
 368
 369     <example>
 370       <title>Extended Start-up Notification</title>
 371
 372       <para>A service could send the following after completing
 373       initialization:</para>
 374
 375       <programlisting>sd_notifyf(0, "READY=1\n"
 376         "STATUS=Processing requests…\n"
 377         "MAINPID=%lu",
 378         (unsigned long) getpid());</programlisting>
 379     </example>
 380
 381     <example>
 382       <title>Error Cause Notification</title>
 383
 384       <para>A service could send the following shortly before exiting, on failure:</para>
 385
 386       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 387         "ERRNO=%i",
 388         strerror(errno),
 389         errno);</programlisting>
 390     </example>
 391
 392     <example>
 393       <title>Store a File Descriptor in the Service Manager</title>
 394
 395       <para>To store an open file descriptor in the service manager,
 396       in order to continue operation after a service restart without
 397       losing state, use <literal>FDSTORE=1</literal>:</para>
 398
 399       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 400     </example>
 401   </refsect1>
 402
 403   <refsect1>
 404     <title>See Also</title>
 405     <para>
 406       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 407       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 408       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 409       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 410       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 411       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 412       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 413     </para>
 414   </refsect1>
 415
 416 </refentry>