man/sd_notify.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   6   This file is part of systemd.
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   8   Copyright 2010 Lennart Poettering
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  23
  24 <refentry id="sd_notify">
  25
  26         <refentryinfo>
  27                 <title>sd_notify</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>sd_notify</refentrytitle>
  42                 <manvolnum>3</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>sd_notify</refname>
  47                 <refname>sd_notifyf</refname>
  48                 <refpurpose>Notify service manager about start-up completion and other daemon status changes</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <funcsynopsis>
  53                         <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  54
  55                         <funcprototype>
  56                                 <funcdef>int <function>sd_notify</function></funcdef>
  57                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
  58                                 <paramdef>const char *<parameter>state</parameter></paramdef>
  59                         </funcprototype>
  60
  61                         <funcprototype>
  62                                 <funcdef>int <function>sd_notifyf</function></funcdef>
  63                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
  64                                 <paramdef>const char *<parameter>format</parameter></paramdef>
  65                                 <paramdef>...</paramdef>
  66                         </funcprototype>
  67                 </funcsynopsis>
  68         </refsynopsisdiv>
  69
  70         <refsect1>
  71                 <title>Description</title>
  72                 <para><function>sd_notify()</function> shall be called
  73                 by a daemon to notify the init system about status
  74                 changes. It can be used to send arbitrary information,
  75                 encoded in an environment-block-like string. Most
  76                 importantly it can be used for start-up completion
  77                 notification.</para>
  78
  79                 <para>If the <parameter>unset_environment</parameter>
  80                 parameter is non-zero, <function>sd_notify()</function>
  81                 will unset the <varname>$NOTIFY_SOCKET</varname>
  82                 environment variable before returning (regardless of
  83                 whether the function call itself succeeded or
  84                 not). Further calls to
  85                 <function>sd_notify()</function> will then fail, but
  86                 the variable is no longer inherited by child
  87                 processes.</para>
  88
  89                 <para>The <parameter>state</parameter> parameter
  90                 should contain a newline-separated list of variable
  91                 assignments, similar in style to an environment
  92                 block. A trailing newline is implied if none is
  93                 specified. The string may contain any kind of variable
  94                 assignments, but the following shall be considered
  95                 well-known:</para>
  96
  97                 <variablelist>
  98                         <varlistentry>
  99                                 <term>READY=1</term>
 100
 101                                 <listitem><para>Tells the init system
 102                                 that daemon startup is finished. This
 103                                 is only used by systemd if the service
 104                                 definition file has Type=notify
 105                                 set. The passed argument is a boolean
 106                                 "1" or "0". Since there is little
 107                                 value in signaling non-readiness, the
 108                                 only value daemons should send is
 109                                 "READY=1".</para></listitem>
 110                         </varlistentry>
 111
 112                         <varlistentry>
 113                                 <term>STATUS=...</term>
 114
 115                                 <listitem><para>Passes a single-line
 116                                 status string back to the init system
 117                                 that describes the daemon state. This
 118                                 is free-form and can be used for
 119                                 various purposes: general state
 120                                 feedback, fsck-like programs could
 121                                 pass completion percentages and
 122                                 failing programs could pass a human
 123                                 readable error message. Example:
 124                                 "STATUS=Completed 66% of file system
 125                                 check..."</para></listitem>
 126                         </varlistentry>
 127
 128                         <varlistentry>
 129                                 <term>ERRNO=...</term>
 130
 131                                 <listitem><para>If a daemon fails, the
 132                                 errno-style error code, formatted as
 133                                 string. Example: "ERRNO=2" for
 134                                 ENOENT.</para></listitem>
 135                         </varlistentry>
 136
 137                         <varlistentry>
 138                                 <term>BUSERROR=...</term>
 139
 140                                 <listitem><para>If a daemon fails, the
 141                                 D-Bus error-style error code. Example:
 142                                 "BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem>
 143                         </varlistentry>
 144
 145                         <varlistentry>
 146                                 <term>MAINPID=...</term>
 147
 148                                 <listitem><para>The main pid of the
 149                                 daemon, in case the init system did
 150                                 not fork off the process
 151                                 itself. Example:
 152                                 "MAINPID=4711"</para></listitem>
 153                         </varlistentry>
 154
 155                         <varlistentry>
 156                                 <term>WATCHDOG=1</term>
 157
 158                                 <listitem><para>Tells systemd to
 159                                 update the watchdog timestamp. This is
 160                                 the keep-alive ping that services need
 161                                 to issue in regular intervals if
 162                                 <varname>WatchdogSec=</varname> is
 163                                 enabled for it. See
 164                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 165                                 for details. It is recommended to send
 166                                 this message if the
 167                                 <varname>$WATCHDOG_PID</varname>
 168                                 environment variable has been set to
 169                                 the PID of the service process, in
 170                                 every half the time interval that is
 171                                 specified in the
 172                                 <varname>$WATCHDOG_USEC</varname>
 173                                 environment variable. See
 174                                 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 175                                 for details.</para></listitem>
 176                         </varlistentry>
 177                 </variablelist>
 178
 179                 <para>It is recommended to prefix variable names that
 180                 are not shown in the list above with
 181                 <varname>X_</varname> to avoid namespace
 182                 clashes.</para>
 183
 184                 <para>Note that systemd will accept status data sent
 185                 from a daemon only if the
 186                 <varname>NotifyAccess=</varname> option is correctly
 187                 set in the service definition file. See
 188                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 189                 for details.</para>
 190
 191                 <para><function>sd_notifyf()</function> is similar to
 192                 <function>sd_notify()</function> but takes a
 193                 <function>printf()</function>-like format string plus
 194                 arguments.</para>
 195         </refsect1>
 196
 197         <refsect1>
 198                 <title>Return Value</title>
 199
 200                 <para>On failure, these calls return a negative
 201                 errno-style error code. If
 202                 <varname>$NOTIFY_SOCKET</varname> was not set and
 203                 hence no status data could be sent, 0 is returned. If
 204                 the status was sent, these functions return with a
 205                 positive return value. In order to support both, init
 206                 systems that implement this scheme and those which
 207                 do not, it is generally recommended to ignore the return
 208                 value of this call.</para>
 209         </refsect1>
 210
 211         <refsect1>
 212                 <title>Notes</title>
 213
 214                 <para>These functions are provided by the reference
 215                 implementation of APIs for new-style daemons and
 216                 distributed with the systemd package. The algorithms
 217                 they implement are simple, and can easily be
 218                 reimplemented in daemons if it is important to support
 219                 this interface without using the reference
 220                 implementation.</para>
 221
 222                 <para>Internally, these functions send a single
 223                 datagram with the state string as payload to the
 224                 <constant>AF_UNIX</constant> socket referenced in the
 225                 <varname>$NOTIFY_SOCKET</varname> environment
 226                 variable. If the first character of
 227                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
 228                 understood as Linux abstract namespace socket. The
 229                 datagram is accompanied by the process credentials of
 230                 the sending daemon, using SCM_CREDENTIALS.</para>
 231
 232                 <para>For details about the algorithms check the
 233                 liberally licensed reference implementation sources:
 234                 <ulink url="http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c"/>
 235                 and <ulink
 236                 url="http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h"/></para>
 237
 238                 <para><function>sd_notify()</function> and
 239                 <function>sd_notifyf()</function> are implemented in
 240                 the reference implementation's
 241                 <filename>sd-daemon.c</filename> and
 242                 <filename>sd-daemon.h</filename> files. These
 243                 interfaces are available as a shared library, which can
 244                 be compiled and linked to with the
 245                 <constant>libsystemd-daemon</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 246                 file. Alternatively, applications consuming these APIs
 247                 may copy the implementation into their source tree. For
 248                 more details about the reference implementation, see
 249                 <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
 250
 251                 <para>If the reference implementation is used as
 252                 drop-in files and -DDISABLE_SYSTEMD is set during
 253                 compilation, these functions will always return 0 and
 254                 otherwise become a NOP.</para>
 255         </refsect1>
 256
 257         <refsect1>
 258                 <title>Environment</title>
 259
 260                 <variablelist class='environment-variables'>
 261                         <varlistentry>
 262                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 263
 264                                 <listitem><para>Set by the init system
 265                                 for supervised processes for status
 266                                 and start-up completion
 267                                 notification. This environment variable
 268                                 specifies the socket
 269                                 <function>sd_notify()</function> talks
 270                                 to. See above for details.</para></listitem>
 271                         </varlistentry>
 272                 </variablelist>
 273         </refsect1>
 274
 275         <refsect1>
 276                 <title>Examples</title>
 277
 278                 <example>
 279                         <title>Start-up Notification</title>
 280
 281                         <para>When a daemon finished starting up, it
 282                         might issue the following call to notify
 283                         the init system:</para>
 284
 285                         <programlisting>sd_notify(0, "READY=1");</programlisting>
 286                 </example>
 287
 288                 <example>
 289                         <title>Extended Start-up Notification</title>
 290
 291                         <para>A daemon could send the following after
 292                         completing initialization:</para>
 293
 294                         <programlisting>sd_notifyf(0, "READY=1\n"
 295               "STATUS=Processing requests...\n"
 296               "MAINPID=%lu",
 297               (unsigned long) getpid());</programlisting>
 298                 </example>
 299
 300                 <example>
 301                         <title>Error Cause Notification</title>
 302
 303                         <para>A daemon could send the following shortly before exiting, on failure</para>
 304
 305                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 306               "ERRNO=%i",
 307               strerror(errno),
 308               errno);</programlisting>
 309                 </example>
 310         </refsect1>
 311
 312         <refsect1>
 313                 <title>See Also</title>
 314                 <para>
 315                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 316                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 317                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 318                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 319                         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 320                 </para>
 321         </refsect1>
 322
 323 </refentry>