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                 <refpurpose>Notify service manager about start-up completion and other service status changes</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <funcsynopsis>
  54                         <funcsynopsisinfo>#include &lt;systemd/sd-daemon.h&gt;</funcsynopsisinfo>
  55
  56                         <funcprototype>
  57                                 <funcdef>int <function>sd_notify</function></funcdef>
  58                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
  59                                 <paramdef>const char *<parameter>state</parameter></paramdef>
  60                         </funcprototype>
  61
  62                         <funcprototype>
  63                                 <funcdef>int <function>sd_notifyf</function></funcdef>
  64                                 <paramdef>int <parameter>unset_environment</parameter></paramdef>
  65                                 <paramdef>const char *<parameter>format</parameter></paramdef>
  66                                 <paramdef>...</paramdef>
  67                         </funcprototype>
  68                 </funcsynopsis>
  69         </refsynopsisdiv>
  70
  71         <refsect1>
  72                 <title>Description</title>
  73                 <para><function>sd_notify()</function> may be called
  74                 by a service to notify the service manager about
  75                 state changes. It can be used to send arbitrary
  76                 information, encoded in an environment-block-like
  77                 string. Most importantly it can be used for start-up
  78                 completion notification.</para>
  79
  80                 <para>If the <parameter>unset_environment</parameter>
  81                 parameter is non-zero, <function>sd_notify()</function>
  82                 will unset the <varname>$NOTIFY_SOCKET</varname>
  83                 environment variable before returning (regardless of
  84                 whether the function call itself succeeded or
  85                 not). Further calls to
  86                 <function>sd_notify()</function> will then fail, but
  87                 the variable is no longer inherited by child
  88                 processes.</para>
  89
  90                 <para>The <parameter>state</parameter> parameter
  91                 should contain a newline-separated list of variable
  92                 assignments, similar in style to an environment
  93                 block. A trailing newline is implied if none is
  94                 specified. The string may contain any kind of variable
  95                 assignments, but the following shall be considered
  96                 well-known:</para>
  97
  98                 <variablelist>
  99                         <varlistentry>
 100                                 <term>READY=1</term>
 101
 102                                 <listitem><para>Tells the service
 103                                 manager that service startup is
 104                                 finished. This is only used by systemd
 105                                 if the service definition file has
 106                                 Type=notify set. Since there is little
 107                                 value in signaling non-readiness, the
 108                                 only value services should send is
 109                                 <literal>READY=1</literal>
 110                                 (i.e. <literal>READY=0</literal> is
 111                                 not defined).</para></listitem>
 112                         </varlistentry>
 113
 114                         <varlistentry>
 115                                 <term>RELOADING=1</term>
 116
 117                                 <listitem><para>Tells the service manager
 118                                 that the service is reloading its
 119                                 configuration. This is useful to allow
 120                                 the service manager to track the service's
 121                                 internal state, and present it to the
 122                                 user. Note that a service that sends
 123                                 this notification must also send a
 124                                 <literal>READY=1</literal>
 125                                 notification when it completed
 126                                 reloading its
 127                                 configuration.</para></listitem>
 128                         </varlistentry>
 129
 130                         <varlistentry>
 131                                 <term>STOPPING=1</term>
 132
 133                                 <listitem><para>Tells the service manager
 134                                 that the service is beginning its
 135                                 shutdown. This is useful to allow the
 136                                 service manager to track the service's
 137                                 internal state, and present it to the
 138                                 user.</para></listitem>
 139                         </varlistentry>
 140
 141                         <varlistentry>
 142                                 <term>STATUS=...</term>
 143
 144                                 <listitem><para>Passes a single-line
 145                                 UTF-8 status string back to the service manager
 146                                 that describes the service state. This
 147                                 is free-form and can be used for
 148                                 various purposes: general state
 149                                 feedback, fsck-like programs could
 150                                 pass completion percentages and
 151                                 failing programs could pass a human
 152                                 readable error message. Example:
 153                                 <literal>STATUS=Completed 66% of file
 154                                 system
 155                                 check...</literal></para></listitem>
 156                         </varlistentry>
 157
 158                         <varlistentry>
 159                                 <term>ERRNO=...</term>
 160
 161                                 <listitem><para>If a service fails, the
 162                                 errno-style error code, formatted as
 163                                 string. Example: <literal>ERRNO=2</literal> for
 164                                 ENOENT.</para></listitem>
 165                         </varlistentry>
 166
 167                         <varlistentry>
 168                                 <term>BUSERROR=...</term>
 169
 170                                 <listitem><para>If a service fails, the
 171                                 D-Bus error-style error code. Example:
 172                                 <literal>BUSERROR=org.freedesktop.DBus.Error.TimedOut</literal></para></listitem>
 173                         </varlistentry>
 174
 175                         <varlistentry>
 176                                 <term>MAINPID=...</term>
 177
 178                                 <listitem><para>The main pid of the
 179                                 service, in case the service manager did
 180                                 not fork off the process
 181                                 itself. Example:
 182                                 <literal>MAINPID=4711</literal></para></listitem>
 183                         </varlistentry>
 184
 185                         <varlistentry>
 186                                 <term>WATCHDOG=1</term>
 187
 188                                 <listitem><para>Tells systemd to
 189                                 update the watchdog timestamp. This is
 190                                 the keep-alive ping that services need
 191                                 to issue in regular intervals if
 192                                 <varname>WatchdogSec=</varname> is
 193                                 enabled for it. See
 194                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 195                                 for details. It is recommended to send
 196                                 this message if the
 197                                 <varname>$WATCHDOG_PID</varname>
 198                                 environment variable has been set to
 199                                 the PID of the service process, in
 200                                 every half the time interval that is
 201                                 specified in the
 202                                 <varname>$WATCHDOG_USEC</varname>
 203                                 environment variable. See
 204                                 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 205                                 for details.</para></listitem>
 206                         </varlistentry>
 207                 </variablelist>
 208
 209                 <para>It is recommended to prefix variable names that
 210                 are not shown in the list above with
 211                 <varname>X_</varname> to avoid namespace
 212                 clashes.</para>
 213
 214                 <para>Note that systemd will accept status data sent
 215                 from a service only if the
 216                 <varname>NotifyAccess=</varname> option is correctly
 217                 set in the service definition file. See
 218                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 219                 for details.</para>
 220
 221                 <para><function>sd_notifyf()</function> is similar to
 222                 <function>sd_notify()</function> but takes a
 223                 <function>printf()</function>-like format string plus
 224                 arguments.</para>
 225         </refsect1>
 226
 227         <refsect1>
 228                 <title>Return Value</title>
 229
 230                 <para>On failure, these calls return a negative
 231                 errno-style error code. If
 232                 <varname>$NOTIFY_SOCKET</varname> was not set and
 233                 hence no status data could be sent, 0 is returned. If
 234                 the status was sent, these functions return with a
 235                 positive return value. In order to support both, init
 236                 systems that implement this scheme and those which
 237                 do not, it is generally recommended to ignore the return
 238                 value of this call.</para>
 239         </refsect1>
 240
 241         <refsect1>
 242                 <title>Notes</title>
 243
 244                 <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 245
 246                 <para>Internally, these functions send a single
 247                 datagram with the state string as payload to the
 248                 <constant>AF_UNIX</constant> socket referenced in the
 249                 <varname>$NOTIFY_SOCKET</varname> environment
 250                 variable. If the first character of
 251                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
 252                 understood as Linux abstract namespace socket. The
 253                 datagram is accompanied by the process credentials of
 254                 the sending service, using SCM_CREDENTIALS.</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 service manager
 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 service finished starting up, it
 282                         might issue the following call to notify
 283                         the service manager:</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 service 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 service 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>