man/sd_notify.xml

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   8   Copyright 2010 Lennart Poettering
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  23
  24 <refentry id="sd_notify"
  25   xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27   <refentryinfo>
  28     <title>sd_notify</title>
  29     <productname>systemd</productname>
  30
  31     <authorgroup>
  32       <author>
  33         <contrib>Developer</contrib>
  34         <firstname>Lennart</firstname>
  35         <surname>Poettering</surname>
  36         <email>lennart@poettering.net</email>
  37       </author>
  38     </authorgroup>
  39   </refentryinfo>
  40
  41   <refmeta>
  42     <refentrytitle>sd_notify</refentrytitle>
  43     <manvolnum>3</manvolnum>
  44   </refmeta>
  45
  46   <refnamediv>
  47     <refname>sd_notify</refname>
  48     <refname>sd_notifyf</refname>
  49     <refname>sd_pid_notify</refname>
  50     <refname>sd_pid_notifyf</refname>
  51     <refname>sd_pid_notify_with_fds</refname>
  52     <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
  53   </refnamediv>
  54
  55   <refsynopsisdiv>
  56     <funcsynopsis>
  57       <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  58
  59       <funcprototype>
  60         <funcdef>int <function>sd_notify</function></funcdef>
  61         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  62         <paramdef>const char *<parameter>state</parameter></paramdef>
  63       </funcprototype>
  64
  65       <funcprototype>
  66         <funcdef>int <function>sd_notifyf</function></funcdef>
  67         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  68         <paramdef>const char *<parameter>format</parameter></paramdef>
  69         <paramdef>…</paramdef>
  70       </funcprototype>
  71
  72       <funcprototype>
  73         <funcdef>int <function>sd_pid_notify</function></funcdef>
  74         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  75         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  76         <paramdef>const char *<parameter>state</parameter></paramdef>
  77       </funcprototype>
  78
  79       <funcprototype>
  80         <funcdef>int <function>sd_pid_notifyf</function></funcdef>
  81         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  82         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  83         <paramdef>const char *<parameter>format</parameter></paramdef>
  84         <paramdef>…</paramdef>
  85       </funcprototype>
  86
  87       <funcprototype>
  88         <funcdef>int <function>sd_pid_notify_with_fds</function></funcdef>
  89         <paramdef>pid_t <parameter>pid</parameter></paramdef>
  90         <paramdef>int <parameter>unset_environment</parameter></paramdef>
  91         <paramdef>const char *<parameter>state</parameter></paramdef>
  92         <paramdef>const int *<parameter>fds</parameter></paramdef>
  93         <paramdef>unsigned <parameter>n_fds</parameter></paramdef>
  94       </funcprototype>
  95     </funcsynopsis>
  96   </refsynopsisdiv>
  97
  98   <refsect1>
  99     <title>Description</title>
 100     <para><function>sd_notify()</function> may be called by a service
 101     to notify the service manager about state changes. It can be used
 102     to send arbitrary information, encoded in an
 103     environment-block-like string. Most importantly, it can be used for
 104     start-up completion notification.</para>
 105
 106     <para>If the <parameter>unset_environment</parameter> parameter is
 107     non-zero, <function>sd_notify()</function> will unset the
 108     <varname>$NOTIFY_SOCKET</varname> environment variable before
 109     returning (regardless of whether the function call itself
 110     succeeded or not). Further calls to
 111     <function>sd_notify()</function> will then fail, but the variable
 112     is no longer inherited by child processes.</para>
 113
 114     <para>The <parameter>state</parameter> parameter should contain a
 115     newline-separated list of variable assignments, similar in style
 116     to an environment block. A trailing newline is implied if none is
 117     specified. The string may contain any kind of variable
 118     assignments, but the following shall be considered
 119     well-known:</para>
 120
 121     <variablelist>
 122       <varlistentry>
 123         <term>READY=1</term>
 124
 125         <listitem><para>Tells the service manager that service startup
 126         is finished. This is only used by systemd if the service
 127         definition file has Type=notify set. Since there is little
 128         value in signaling non-readiness, the only value services
 129         should send is <literal>READY=1</literal> (i.e.
 130         <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.</para></listitem>
 143       </varlistentry>
 144
 145       <varlistentry>
 146         <term>STOPPING=1</term>
 147
 148         <listitem><para>Tells the service manager that the service is
 149         beginning its shutdown. This is useful to allow the service
 150         manager to track the service's internal state, and present it
 151         to the user.</para></listitem>
 152       </varlistentry>
 153
 154       <varlistentry>
 155         <term>STATUS=…</term>
 156
 157         <listitem><para>Passes a single-line UTF-8 status string back
 158         to the service manager that describes the service state. This
 159         is free-form and can be used for various purposes: general
 160         state feedback, fsck-like programs could pass completion
 161         percentages and failing programs could pass a human-readable
 162         error message. Example: <literal>STATUS=Completed 66% of file
 163         system check…</literal></para></listitem>
 164       </varlistentry>
 165
 166       <varlistentry>
 167         <term>ERRNO=…</term>
 168
 169         <listitem><para>If a service fails, the errno-style error
 170         code, formatted as string. Example: <literal>ERRNO=2</literal>
 171         for ENOENT.</para></listitem>
 172       </varlistentry>
 173
 174       <varlistentry>
 175         <term>BUSERROR=…</term>
 176
 177         <listitem><para>If a service fails, the D-Bus error-style
 178         error code. Example:
 179         <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 180       </varlistentry>
 181
 182       <varlistentry>
 183         <term>MAINPID=…</term>
 184
 185         <listitem><para>The main process ID (PID) of the service, in
 186         case the service manager did not fork off the process itself.
 187         Example: <literal>MAINPID=4711</literal></para></listitem>
 188       </varlistentry>
 189
 190       <varlistentry>
 191         <term>WATCHDOG=1</term>
 192
 193         <listitem><para>Tells the service manager to update the
 194         watchdog timestamp. This is the keep-alive ping that services
 195         need to issue in regular intervals if
 196         <varname>WatchdogSec=</varname> is enabled for it. See
 197         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 198         for information how to enable this functionality and
 199         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 200         for the details of how the service can check whether the
 201         watchdog is enabled. </para></listitem>
 202       </varlistentry>
 203
 204
 205       <varlistentry>
 206         <term>FDSTORE=1</term>
 207
 208         <listitem><para>Stores additional file descriptors in the service manager. File descriptors sent this way will
 209         be maintained per-service by the service manager and will later be handed back using the usual file descriptor
 210         passing logic at the next invocation of the service, see
 211         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.  This is
 212         useful for implementing services that can restart after an explicit request or a crash without losing
 213         state. Any open sockets and other file descriptors which should not be closed during the restart may be stored
 214         this way. Application state can either be serialized to a file in <filename>/run</filename>, or better, stored
 215         in a <citerefentry><refentrytitle>memfd_create</refentrytitle><manvolnum>2</manvolnum></citerefentry> memory
 216         file descriptor. Note that the service manager will accept messages for a service only if its
 217         <varname>FileDescriptorStoreMax=</varname> setting is non-zero (defaults to zero, see
 218         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>). If file
 219         descriptors sent are pollable (see
 220         <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>), then any
 221         <constant>EPOLLHUP</constant> or <constant>EPOLLERR</constant> event seen on them will result in their
 222         automatic removal from the store. Multiple arrays of file descriptors may be sent in separate messages, in
 223         which case the arrays are combined. Note that the service manager removes duplicate (pointing to the same
 224         object) file descriptors before passing them to the service. Use <function>sd_pid_notify_with_fds()</function>
 225         to send messages with <literal>FDSTORE=1</literal>, see below.</para></listitem>
 226       </varlistentry>
 227
 228       <varlistentry>
 229         <term>FDNAME=…</term>
 230
 231         <listitem><para>When used in combination with
 232         <varname>FDSTORE=1</varname>, specifies a name for the
 233         submitted file descriptors. This name is passed to the service
 234         during activation, and may be queried using
 235         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 236         descriptors submitted without this field set, will implicitly
 237         get the name <literal>stored</literal> assigned. Note that, if
 238         multiple file descriptors are submitted at once, the specified
 239         name will be assigned to all of them. In order to assign
 240         different names to submitted file descriptors, submit them in
 241         separate invocations of
 242         <function>sd_pid_notify_with_fds()</function>. The name may
 243         consist of any ASCII character, but must not contain control
 244         characters or <literal>:</literal>. It may not be longer than
 245         255 characters. If a submitted name does not follow these
 246         restrictions, it is ignored.</para></listitem>
 247       </varlistentry>
 248
 249       <varlistentry>
 250         <term>WATCHDOG_USEC=…</term>
 251
 252         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 253         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 254         or <function>sd_watchdog_enabled()</function>.
 255         Example : <literal>WATCHDOG_USEC=20000000</literal></para></listitem>
 256       </varlistentry>
 257
 258     </variablelist>
 259
 260     <para>It is recommended to prefix variable names that are not
 261     listed above with <varname>X_</varname> to avoid namespace
 262     clashes.</para>
 263
 264     <para>Note that systemd will accept status data sent from a
 265     service only if the <varname>NotifyAccess=</varname> option is
 266     correctly set in the service definition file. See
 267     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 268     for details.</para>
 269
 270     <para>Note that <function>sd_notify()</function> notifications may be attributed to units correctly only if either
 271     the sending process is still around at the time PID 1 processes the message, or if the sending process is
 272     explicitly runtime-tracked by the service manager. The latter is the case if the service manager originally forked
 273     off the process, i.e. on all processes that match <varname>NotifyAccess=</varname><option>main</option> or
 274     <varname>NotifyAccess=</varname><option>exec</option>. Conversely, if an auxiliary process of the unit sends an
 275     <function>sd_notify()</function> message and immediately exits, the service manager might not be able to properly
 276     attribute the message to the unit, and thus will ignore it, even if
 277     <varname>NotifyAccess=</varname><option>all</option> is set for it.</para>
 278
 279     <para><function>sd_notifyf()</function> is similar to
 280     <function>sd_notify()</function> but takes a
 281     <function>printf()</function>-like format string plus
 282     arguments.</para>
 283
 284     <para><function>sd_pid_notify()</function> and
 285     <function>sd_pid_notifyf()</function> are similar to
 286     <function>sd_notify()</function> and
 287     <function>sd_notifyf()</function> but take a process ID (PID) to
 288     use as originating PID for the message as first argument. This is
 289     useful to send notification messages on behalf of other processes,
 290     provided the appropriate privileges are available. If the PID
 291     argument is specified as 0, the process ID of the calling process
 292     is used, in which case the calls are fully equivalent to
 293     <function>sd_notify()</function> and
 294     <function>sd_notifyf()</function>.</para>
 295
 296     <para><function>sd_pid_notify_with_fds()</function> is similar to
 297     <function>sd_pid_notify()</function> but takes an additional array
 298     of file descriptors. These file descriptors are sent along the
 299     notification message to the service manager. This is particularly
 300     useful for sending <literal>FDSTORE=1</literal> messages, as
 301     described above. The additional arguments are a pointer to the
 302     file descriptor array plus the number of file descriptors in the
 303     array. If the number of file descriptors is passed as 0, the call
 304     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 305     no file descriptors are passed. Note that sending file descriptors
 306     to the service manager on messages that do not expect them (i.e.
 307     without <literal>FDSTORE=1</literal>) they are immediately closed
 308     on reception.</para>
 309   </refsect1>
 310
 311   <refsect1>
 312     <title>Return Value</title>
 313
 314     <para>On failure, these calls return a negative errno-style error code. If <varname>$NOTIFY_SOCKET</varname> was
 315     not set and hence no status message could be sent, 0 is returned. If the status was sent, these functions return a
 316     positive value. In order to support both service managers that implement this scheme and those which do not, it is
 317     generally recommended to ignore the return value of this call. Note that the return value simply indicates whether
 318     the notification message was enqueued properly, it does not reflect whether the message could be processed
 319     successfully. Specifically, no error is returned when a file descriptor is attempted to be stored using
 320     <varname>FDSTORE=1</varname> but the service is not actually configured to permit storing of file descriptors (see
 321     above).</para>
 322   </refsect1>
 323
 324   <refsect1>
 325     <title>Notes</title>
 326
 327     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 328
 329     <para>These functions send a single datagram with the
 330     state string as payload to the <constant>AF_UNIX</constant> socket
 331     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 332     variable. If the first character of
 333     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 334     string is understood as Linux abstract namespace socket. The
 335     datagram is accompanied by the process credentials of the sending
 336     service, using SCM_CREDENTIALS.</para>
 337   </refsect1>
 338
 339   <refsect1>
 340     <title>Environment</title>
 341
 342     <variablelist class='environment-variables'>
 343       <varlistentry>
 344         <term><varname>$NOTIFY_SOCKET</varname></term>
 345
 346         <listitem><para>Set by the service manager for supervised
 347         processes for status and start-up completion notification.
 348         This environment variable specifies the socket
 349         <function>sd_notify()</function> talks to. See above for
 350         details.</para></listitem>
 351       </varlistentry>
 352     </variablelist>
 353   </refsect1>
 354
 355   <refsect1>
 356     <title>Examples</title>
 357
 358     <example>
 359       <title>Start-up Notification</title>
 360
 361       <para>When a service finished starting up, it might issue the
 362       following call to notify the service manager:</para>
 363
 364       <programlisting>sd_notify(0, "READY=1");</programlisting>
 365     </example>
 366
 367     <example>
 368       <title>Extended Start-up Notification</title>
 369
 370       <para>A service could send the following after completing
 371       initialization:</para>
 372
 373       <programlisting>sd_notifyf(0, "READY=1\n"
 374         "STATUS=Processing requests…\n"
 375         "MAINPID=%lu",
 376         (unsigned long) getpid());</programlisting>
 377     </example>
 378
 379     <example>
 380       <title>Error Cause Notification</title>
 381
 382       <para>A service could send the following shortly before exiting, on failure:</para>
 383
 384       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 385         "ERRNO=%i",
 386         strerror(errno),
 387         errno);</programlisting>
 388     </example>
 389
 390     <example>
 391       <title>Store a File Descriptor in the Service Manager</title>
 392
 393       <para>To store an open file descriptor in the service manager,
 394       in order to continue operation after a service restart without
 395       losing state, use <literal>FDSTORE=1</literal>:</para>
 396
 397       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 398     </example>
 399   </refsect1>
 400
 401   <refsect1>
 402     <title>See Also</title>
 403     <para>
 404       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 405       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 406       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 407       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 408       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 409       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 410       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 411     </para>
 412   </refsect1>
 413
 414 </refentry>