man/sd_notify.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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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
 101                 by a service to notify the service manager about
 102                 state changes. It can be used to send arbitrary
 103                 information, encoded in an environment-block-like
 104                 string. Most importantly it can be used for start-up
 105                 completion notification.</para>
 106
 107                 <para>If the <parameter>unset_environment</parameter>
 108                 parameter is non-zero, <function>sd_notify()</function>
 109                 will unset the <varname>$NOTIFY_SOCKET</varname>
 110                 environment variable before returning (regardless of
 111                 whether the function call itself succeeded or
 112                 not). Further calls to
 113                 <function>sd_notify()</function> will then fail, but
 114                 the variable is no longer inherited by child
 115                 processes.</para>
 116
 117                 <para>The <parameter>state</parameter> parameter
 118                 should contain a newline-separated list of variable
 119                 assignments, similar in style to an environment
 120                 block. A trailing newline is implied if none is
 121                 specified. The string may contain any kind of variable
 122                 assignments, but the following shall be considered
 123                 well-known:</para>
 124
 125                 <variablelist>
 126                         <varlistentry>
 127                                 <term>READY=1</term>
 128
 129                                 <listitem><para>Tells the service
 130                                 manager that service startup is
 131                                 finished. This is only used by systemd
 132                                 if the service definition file has
 133                                 Type=notify set. Since there is little
 134                                 value in signaling non-readiness, the
 135                                 only value services should send is
 136                                 <literal>READY=1</literal>
 137                                 (i.e. <literal>READY=0</literal> is
 138                                 not defined).</para></listitem>
 139                         </varlistentry>
 140
 141                         <varlistentry>
 142                                 <term>RELOADING=1</term>
 143
 144                                 <listitem><para>Tells the service manager
 145                                 that the service is reloading its
 146                                 configuration. This is useful to allow
 147                                 the service manager to track the service's
 148                                 internal state, and present it to the
 149                                 user. Note that a service that sends
 150                                 this notification must also send a
 151                                 <literal>READY=1</literal>
 152                                 notification when it completed
 153                                 reloading its
 154                                 configuration.</para></listitem>
 155                         </varlistentry>
 156
 157                         <varlistentry>
 158                                 <term>STOPPING=1</term>
 159
 160                                 <listitem><para>Tells the service manager
 161                                 that the service is beginning its
 162                                 shutdown. This is useful to allow the
 163                                 service manager to track the service's
 164                                 internal state, and present it to the
 165                                 user.</para></listitem>
 166                         </varlistentry>
 167
 168                         <varlistentry>
 169                                 <term>STATUS=...</term>
 170
 171                                 <listitem><para>Passes a single-line
 172                                 UTF-8 status string back to the service manager
 173                                 that describes the service state. This
 174                                 is free-form and can be used for
 175                                 various purposes: general state
 176                                 feedback, fsck-like programs could
 177                                 pass completion percentages and
 178                                 failing programs could pass a human
 179                                 readable error message. Example:
 180                                 <literal>STATUS=Completed 66% of file
 181                                 system
 182                                 check...</literal></para></listitem>
 183                         </varlistentry>
 184
 185                         <varlistentry>
 186                                 <term>ERRNO=...</term>
 187
 188                                 <listitem><para>If a service fails, the
 189                                 errno-style error code, formatted as
 190                                 string. Example: <literal>ERRNO=2</literal> for
 191                                 ENOENT.</para></listitem>
 192                         </varlistentry>
 193
 194                         <varlistentry>
 195                                 <term>BUSERROR=...</term>
 196
 197                                 <listitem><para>If a service fails, the
 198                                 D-Bus error-style error code. Example:
 199                                 <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 200                         </varlistentry>
 201
 202                         <varlistentry>
 203                                 <term>MAINPID=...</term>
 204
 205                                 <listitem><para>The main process ID (PID) of the
 206                                 service, in case the service manager did
 207                                 not fork off the process
 208                                 itself. Example:
 209                                 <literal>MAINPID=4711</literal></para></listitem>
 210                         </varlistentry>
 211
 212                         <varlistentry>
 213                                 <term>WATCHDOG=1</term>
 214
 215                                 <listitem><para>Tells the service manager to
 216                                 update the watchdog timestamp. This is
 217                                 the keep-alive ping that services need
 218                                 to issue in regular intervals if
 219                                 <varname>WatchdogSec=</varname> is
 220                                 enabled for it. See
 221                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 222                                 for information how to enable this
 223                                 functionality and
 224                                 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 225                                 for the details of how the service can
 226                                 check if the the watchdog is enabled.
 227                                 </para></listitem>
 228                         </varlistentry>
 229
 230
 231                         <varlistentry>
 232                                 <term>FDSTORE=1</term>
 233
 234                                 <listitem><para>Stores additional file
 235                                 descriptors in the service
 236                                 manager. File descriptors sent this
 237                                 way will be maintained per-service by
 238                                 the service manager and be passed
 239                                 again using the usual file descriptor
 240                                 passing logic on the next invocation
 241                                 of the service (see
 242                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>). This
 243                                 is useful for implementing service
 244                                 restart schemes where services
 245                                 serialize their state to
 246                                 <filename>/run</filename>, push their
 247                                 file descriptors to the system
 248                                 manager, and are then restarted,
 249                                 retrieving their state again via
 250                                 socket passing and
 251                                 <filename>/run</filename>. Note that
 252                                 the service manager will accept
 253                                 messages for a service only if
 254                                 <varname>FileDescriptorStoreMax=</varname>
 255                                 is set to non-zero for it (defaults to
 256                                 zero). See
 257                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 258                                 for details. Multiple arrays of file
 259                                 descriptors may be sent in seperate
 260                                 messages, in which case the arrays are
 261                                 combined. Note that the service
 262                                 manager removes duplicate file
 263                                 descriptors before passing them to the
 264                                 service. Use
 265                                 <function>sd_pid_notify_with_fds()</function>
 266                                 to send messages with
 267                                 <literal>FDSTORE=1</literal>, see
 268                                 below.</para></listitem>
 269                         </varlistentry>
 270
 271                 </variablelist>
 272
 273                 <para>It is recommended to prefix variable names that
 274                 are not listed above with <varname>X_</varname> to
 275                 avoid namespace clashes.</para>
 276
 277                 <para>Note that systemd will accept status data sent
 278                 from a service only if the
 279                 <varname>NotifyAccess=</varname> option is correctly
 280                 set in the service definition file. See
 281                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 282                 for details.</para>
 283
 284                 <para><function>sd_notifyf()</function> is similar to
 285                 <function>sd_notify()</function> but takes a
 286                 <function>printf()</function>-like format string plus
 287                 arguments.</para>
 288
 289                 <para><function>sd_pid_notify()</function> and
 290                 <function>sd_pid_notifyf()</function> are similar to
 291                 <function>sd_notify()</function> and
 292                 <function>sd_notifyf()</function> but take a process
 293                 ID (PID) to use as originating PID for the message as
 294                 first argument. This is useful to send notification
 295                 messages on behalf of other processes, provided the
 296                 appropriate privileges are available. If the PID
 297                 argument is specified as 0 the process ID of the
 298                 calling process is used, in which case the calls are
 299                 fully equivalent to <function>sd_notify()</function>
 300                 and <function>sd_notifyf()</function>.</para>
 301
 302                 <para><function>sd_pid_notify_with_fds()</function> is
 303                 similar to <function>sd_pid_notify()</function> but
 304                 takes an additional array of file descriptors. These
 305                 file descriptors are sent along the notification
 306                 message to the service manager. This is particularly
 307                 useful for sending <literal>FDSTORE=1</literal>
 308                 messages, as described above. The additional arguments
 309                 are a pointer to the file descriptor array plus the
 310                 number of file descriptors in the array. If the number
 311                 of file descriptors is passed as 0, the call is fully
 312                 equivalent to <function>sd_pid_notify()</function>,
 313                 i.e. no file descriptors are passed. Note that sending
 314                 file descriptors to the service manager on messages
 315                 that do not expect them (i.e. without
 316                 <literal>FDSTORE=1</literal>) they are immediately
 317                 closed on reception.</para>
 318         </refsect1>
 319
 320         <refsect1>
 321                 <title>Return Value</title>
 322
 323                 <para>On failure, these calls return a negative
 324                 errno-style error code. If
 325                 <varname>$NOTIFY_SOCKET</varname> was not set and
 326                 hence no status data could be sent, 0 is returned. If
 327                 the status was sent, these functions return with a
 328                 positive return value. In order to support both, init
 329                 systems that implement this scheme and those which
 330                 do not, it is generally recommended to ignore the return
 331                 value of this call.</para>
 332         </refsect1>
 333
 334         <refsect1>
 335                 <title>Notes</title>
 336
 337                 <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 338
 339                 <para>Internally, these functions send a single
 340                 datagram with the state string as payload to the
 341                 <constant>AF_UNIX</constant> socket referenced in the
 342                 <varname>$NOTIFY_SOCKET</varname> environment
 343                 variable. If the first character of
 344                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
 345                 understood as Linux abstract namespace socket. The
 346                 datagram is accompanied by the process credentials of
 347                 the sending service, using SCM_CREDENTIALS.</para>
 348         </refsect1>
 349
 350         <refsect1>
 351                 <title>Environment</title>
 352
 353                 <variablelist class='environment-variables'>
 354                         <varlistentry>
 355                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 356
 357                                 <listitem><para>Set by the service manager
 358                                 for supervised processes for status
 359                                 and start-up completion
 360                                 notification. This environment variable
 361                                 specifies the socket
 362                                 <function>sd_notify()</function> talks
 363                                 to. See above for details.</para></listitem>
 364                         </varlistentry>
 365                 </variablelist>
 366         </refsect1>
 367
 368         <refsect1>
 369                 <title>Examples</title>
 370
 371                 <example>
 372                         <title>Start-up Notification</title>
 373
 374                         <para>When a service finished starting up, it
 375                         might issue the following call to notify
 376                         the service manager:</para>
 377
 378                         <programlisting>sd_notify(0, "READY=1");</programlisting>
 379                 </example>
 380
 381                 <example>
 382                         <title>Extended Start-up Notification</title>
 383
 384                         <para>A service could send the following after
 385                         completing initialization:</para>
 386
 387                         <programlisting>sd_notifyf(0, "READY=1\n"
 388               "STATUS=Processing requests...\n"
 389               "MAINPID=%lu",
 390               (unsigned long) getpid());</programlisting>
 391                 </example>
 392
 393                 <example>
 394                         <title>Error Cause Notification</title>
 395
 396                         <para>A service could send the following shortly before exiting, on failure:</para>
 397
 398                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 399               "ERRNO=%i",
 400               strerror(errno),
 401               errno);</programlisting>
 402                 </example>
 403
 404                 <example>
 405                         <title>Store a File Descriptor in the Service Manager</title>
 406
 407                         <para>To store an open file descriptor in the
 408                         service manager, in order to continue
 409                         operation after a service restart without
 410                         losing state use
 411                         <literal>FDSTORE=1</literal>:</para>
 412
 413                         <programlisting>sd_pid_notify_with_fds(0, 0, "FDSTORE=1", &amp;fd, 1);</programlisting>
 414                 </example>
 415         </refsect1>
 416
 417         <refsect1>
 418                 <title>See Also</title>
 419                 <para>
 420                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 421                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 422                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 423                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 424                         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 425                 </para>
 426         </refsect1>
 427
 428 </refentry>