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
 209         descriptors sent this way will be maintained per-service by the service manager
 210         and will be passed again using the usual file descriptor passing logic on the next
 211         invocation of the service, see
 212         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
 213         This is useful for implementing service restart schemes where services serialize
 214         their state to <filename>/run</filename>, push their file descriptors to the
 215         system manager, and are then restarted, retrieving their state again via socket
 216         passing and <filename>/run</filename>. Note that the service manager will accept
 217         messages for a service only if <varname>FileDescriptorStoreMax=</varname> is set
 218         to non-zero for it (defaults to zero, see
 219         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 220         File descriptors must be pollable, see
 221         <citerefentry><refentrytitle>epoll_ctl</refentrytitle><manvolnum>2</manvolnum></citerefentry>.
 222         Multiple arrays of file descriptors may be sent in separate messages, in which
 223         case the arrays are combined.  Note that the service manager removes duplicate
 224         file descriptors before passing them to the service. Use
 225         <function>sd_pid_notify_with_fds()</function> to send messages with
 226         <literal>FDSTORE=1</literal>, see below.</para></listitem>
 227       </varlistentry>
 228
 229       <varlistentry>
 230         <term>FDNAME=…</term>
 231
 232         <listitem><para>When used in combination with
 233         <varname>FDSTORE=1</varname>, specifies a name for the
 234         submitted file descriptors. This name is passed to the service
 235         during activation, and may be queried using
 236         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 237         descriptors submitted without this field set, will implicitly
 238         get the name <literal>stored</literal> assigned. Note that, if
 239         multiple file descriptors are submitted at once, the specified
 240         name will be assigned to all of them. In order to assign
 241         different names to submitted file descriptors, submit them in
 242         separate invocations of
 243         <function>sd_pid_notify_with_fds()</function>. The name may
 244         consist of any ASCII character, but must not contain control
 245         characters or <literal>:</literal>. It may not be longer than
 246         255 characters. If a submitted name does not follow these
 247         restrictions, it is ignored.</para></listitem>
 248       </varlistentry>
 249
 250       <varlistentry>
 251         <term>WATCHDOG_USEC=…</term>
 252
 253         <listitem><para>Reset <varname>watchdog_usec</varname> value during runtime.
 254         Notice that this is not available when using <function>sd_event_set_watchdog()</function>
 255         or <function>sd_watchdog_enabled()</function>.
 256         Example : <literal>WATCHDOG_USEC=20000000</literal></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
 316     code. If <varname>$NOTIFY_SOCKET</varname> was not set and hence
 317     no status data could be sent, 0 is returned. If the status was
 318     sent, these functions return with a positive return value. In
 319     order to support both, init systems that implement this scheme and
 320     those which do not, it is generally recommended to ignore the
 321     return value of this call.</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>