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 information how to enable this
 196                                 functionality and
 197                                 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 198                                 for the details of how the service can
 199                                 check if the the watchdog is enabled.
 200                                 </para></listitem>
 201                         </varlistentry>
 202                 </variablelist>
 203
 204                 <para>It is recommended to prefix variable names that
 205                 are not shown in the list above with
 206                 <varname>X_</varname> to avoid namespace
 207                 clashes.</para>
 208
 209                 <para>Note that systemd will accept status data sent
 210                 from a service only if the
 211                 <varname>NotifyAccess=</varname> option is correctly
 212                 set in the service definition file. See
 213                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 214                 for details.</para>
 215
 216                 <para><function>sd_notifyf()</function> is similar to
 217                 <function>sd_notify()</function> but takes a
 218                 <function>printf()</function>-like format string plus
 219                 arguments.</para>
 220         </refsect1>
 221
 222         <refsect1>
 223                 <title>Return Value</title>
 224
 225                 <para>On failure, these calls return a negative
 226                 errno-style error code. If
 227                 <varname>$NOTIFY_SOCKET</varname> was not set and
 228                 hence no status data could be sent, 0 is returned. If
 229                 the status was sent, these functions return with a
 230                 positive return value. In order to support both, init
 231                 systems that implement this scheme and those which
 232                 do not, it is generally recommended to ignore the return
 233                 value of this call.</para>
 234         </refsect1>
 235
 236         <refsect1>
 237                 <title>Notes</title>
 238
 239                 <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 240
 241                 <para>Internally, these functions send a single
 242                 datagram with the state string as payload to the
 243                 <constant>AF_UNIX</constant> socket referenced in the
 244                 <varname>$NOTIFY_SOCKET</varname> environment
 245                 variable. If the first character of
 246                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
 247                 understood as Linux abstract namespace socket. The
 248                 datagram is accompanied by the process credentials of
 249                 the sending service, using SCM_CREDENTIALS.</para>
 250         </refsect1>
 251
 252         <refsect1>
 253                 <title>Environment</title>
 254
 255                 <variablelist class='environment-variables'>
 256                         <varlistentry>
 257                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 258
 259                                 <listitem><para>Set by the service manager
 260                                 for supervised processes for status
 261                                 and start-up completion
 262                                 notification. This environment variable
 263                                 specifies the socket
 264                                 <function>sd_notify()</function> talks
 265                                 to. See above for details.</para></listitem>
 266                         </varlistentry>
 267                 </variablelist>
 268         </refsect1>
 269
 270         <refsect1>
 271                 <title>Examples</title>
 272
 273                 <example>
 274                         <title>Start-up Notification</title>
 275
 276                         <para>When a service finished starting up, it
 277                         might issue the following call to notify
 278                         the service manager:</para>
 279
 280                         <programlisting>sd_notify(0, "READY=1");</programlisting>
 281                 </example>
 282
 283                 <example>
 284                         <title>Extended Start-up Notification</title>
 285
 286                         <para>A service could send the following after
 287                         completing initialization:</para>
 288
 289                         <programlisting>sd_notifyf(0, "READY=1\n"
 290               "STATUS=Processing requests...\n"
 291               "MAINPID=%lu",
 292               (unsigned long) getpid());</programlisting>
 293                 </example>
 294
 295                 <example>
 296                         <title>Error Cause Notification</title>
 297
 298                         <para>A service could send the following shortly before exiting, on failure</para>
 299
 300                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 301               "ERRNO=%i",
 302               strerror(errno),
 303               errno);</programlisting>
 304                 </example>
 305         </refsect1>
 306
 307         <refsect1>
 308                 <title>See Also</title>
 309                 <para>
 310                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 311                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 312                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 313                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 314                         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 315                 </para>
 316         </refsect1>
 317
 318 </refentry>