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
 209         service manager. File descriptors sent this way will be
 210         maintained per-service by the service manager and be passed
 211         again using the usual file descriptor passing logic on the
 212         next invocation of the service (see
 213         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>).
 214         This is useful for implementing service restart schemes where
 215         services serialize their state to <filename>/run</filename>,
 216         push their file descriptors to the system manager, and are
 217         then restarted, retrieving their state again via socket
 218         passing and <filename>/run</filename>. Note that the service
 219         manager will accept messages for a service only if
 220         <varname>FileDescriptorStoreMax=</varname> is set to non-zero
 221         for it (defaults to zero). See
 222         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 223         for details. Multiple arrays of file descriptors may be sent
 224         in separate messages, in which case the arrays are combined.
 225         Note that the service manager removes duplicate file
 226         descriptors before passing them to the service. Use
 227         <function>sd_pid_notify_with_fds()</function> to send messages
 228         with <literal>FDSTORE=1</literal>, see
 229         below.</para></listitem>
 230       </varlistentry>
 231
 232       <varlistentry>
 233         <term>FDNAME=...</term>
 234
 235         <listitem><para>When used in combination with
 236         <varname>FDSTORE=1</varname>, specifies a name for the
 237         submitted file descriptors. This name is passed to the service
 238         during activation, and may be queried using
 239         <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>. File
 240         descriptors submitted without this field set, will implicitly
 241         get the name <literal>stored</literal> assigned. Note that, if
 242         multiple file descriptors are submitted at once, the specified
 243         name will be assigned to all of them. In order to assign
 244         different names to submitted file descriptors, submit them in
 245         seperate invocations of
 246         <function>sd_pid_notify_with_fds()</function>. The name may
 247         consist of any ASCII characters, but must not contain control
 248         characters or <literal>:</literal>. It may not be longer than
 249         255 characters. If a submitted name does not follow these
 250         restrictions, it is ignored.</para></listitem>
 251       </varlistentry>
 252
 253     </variablelist>
 254
 255     <para>It is recommended to prefix variable names that are not
 256     listed above with <varname>X_</varname> to avoid namespace
 257     clashes.</para>
 258
 259     <para>Note that systemd will accept status data sent from a
 260     service only if the <varname>NotifyAccess=</varname> option is
 261     correctly set in the service definition file. See
 262     <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 263     for details.</para>
 264
 265     <para><function>sd_notifyf()</function> is similar to
 266     <function>sd_notify()</function> but takes a
 267     <function>printf()</function>-like format string plus
 268     arguments.</para>
 269
 270     <para><function>sd_pid_notify()</function> and
 271     <function>sd_pid_notifyf()</function> are similar to
 272     <function>sd_notify()</function> and
 273     <function>sd_notifyf()</function> but take a process ID (PID) to
 274     use as originating PID for the message as first argument. This is
 275     useful to send notification messages on behalf of other processes,
 276     provided the appropriate privileges are available. If the PID
 277     argument is specified as 0, the process ID of the calling process
 278     is used, in which case the calls are fully equivalent to
 279     <function>sd_notify()</function> and
 280     <function>sd_notifyf()</function>.</para>
 281
 282     <para><function>sd_pid_notify_with_fds()</function> is similar to
 283     <function>sd_pid_notify()</function> but takes an additional array
 284     of file descriptors. These file descriptors are sent along the
 285     notification message to the service manager. This is particularly
 286     useful for sending <literal>FDSTORE=1</literal> messages, as
 287     described above. The additional arguments are a pointer to the
 288     file descriptor array plus the number of file descriptors in the
 289     array. If the number of file descriptors is passed as 0, the call
 290     is fully equivalent to <function>sd_pid_notify()</function>, i.e.
 291     no file descriptors are passed. Note that sending file descriptors
 292     to the service manager on messages that do not expect them (i.e.
 293     without <literal>FDSTORE=1</literal>) they are immediately closed
 294     on reception.</para>
 295   </refsect1>
 296
 297   <refsect1>
 298     <title>Return Value</title>
 299
 300     <para>On failure, these calls return a negative errno-style error
 301     code. If <varname>$NOTIFY_SOCKET</varname> was not set and hence
 302     no status data could be sent, 0 is returned. If the status was
 303     sent, these functions return with a positive return value. In
 304     order to support both, init systems that implement this scheme and
 305     those which do not, it is generally recommended to ignore the
 306     return value of this call.</para>
 307   </refsect1>
 308
 309   <refsect1>
 310     <title>Notes</title>
 311
 312     <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 313
 314     <para>These functions send a single datagram with the
 315     state string as payload to the <constant>AF_UNIX</constant> socket
 316     referenced in the <varname>$NOTIFY_SOCKET</varname> environment
 317     variable. If the first character of
 318     <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the
 319     string is understood as Linux abstract namespace socket. The
 320     datagram is accompanied by the process credentials of the sending
 321     service, using SCM_CREDENTIALS.</para>
 322   </refsect1>
 323
 324   <refsect1>
 325     <title>Environment</title>
 326
 327     <variablelist class='environment-variables'>
 328       <varlistentry>
 329         <term><varname>$NOTIFY_SOCKET</varname></term>
 330
 331         <listitem><para>Set by the service manager for supervised
 332         processes for status and start-up completion notification.
 333         This environment variable specifies the socket
 334         <function>sd_notify()</function> talks to. See above for
 335         details.</para></listitem>
 336       </varlistentry>
 337     </variablelist>
 338   </refsect1>
 339
 340   <refsect1>
 341     <title>Examples</title>
 342
 343     <example>
 344       <title>Start-up Notification</title>
 345
 346       <para>When a service finished starting up, it might issue the
 347       following call to notify the service manager:</para>
 348
 349       <programlisting>sd_notify(0, "READY=1");</programlisting>
 350     </example>
 351
 352     <example>
 353       <title>Extended Start-up Notification</title>
 354
 355       <para>A service could send the following after completing
 356       initialization:</para>
 357
 358       <programlisting>sd_notifyf(0, "READY=1\n"
 359         "STATUS=Processing requests...\n"
 360         "MAINPID=%lu",
 361         (unsigned long) getpid());</programlisting>
 362     </example>
 363
 364     <example>
 365       <title>Error Cause Notification</title>
 366
 367       <para>A service could send the following shortly before exiting, on failure:</para>
 368
 369       <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 370         "ERRNO=%i",
 371         strerror(errno),
 372         errno);</programlisting>
 373     </example>
 374
 375     <example>
 376       <title>Store a File Descriptor in the Service Manager</title>
 377
 378       <para>To store an open file descriptor in the service manager,
 379       in order to continue operation after a service restart without
 380       losing state, use <literal>FDSTORE=1</literal>:</para>
 381
 382       <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1\nFDNAME=foobar", &amp;fd, 1);</programlisting>
 383     </example>
 384   </refsect1>
 385
 386   <refsect1>
 387     <title>See Also</title>
 388     <para>
 389       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 390       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 391       <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 392       <citerefentry><refentrytitle>sd_listen_fds_with_names</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 393       <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 394       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 395       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 396     </para>
 397   </refsect1>
 398
 399 </refentry>