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 daemon 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> shall be called
  74                 by a daemon to notify the init system about status
  75                 changes. It can be used to send arbitrary information,
  76                 encoded in an environment-block-like string. Most
  77                 importantly it can be used for start-up completion
  78                 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 init system
 103                                 that daemon startup is finished. This
 104                                 is only used by systemd if the service
 105                                 definition file has Type=notify
 106                                 set. The passed argument is a boolean
 107                                 "1" or "0". Since there is little
 108                                 value in signaling non-readiness, the
 109                                 only value daemons should send is
 110                                 "READY=1".</para></listitem>
 111                         </varlistentry>
 112
 113                         <varlistentry>
 114                                 <term>STATUS=...</term>
 115
 116                                 <listitem><para>Passes a single-line
 117                                 status string back to the init system
 118                                 that describes the daemon state. This
 119                                 is free-form and can be used for
 120                                 various purposes: general state
 121                                 feedback, fsck-like programs could
 122                                 pass completion percentages and
 123                                 failing programs could pass a human
 124                                 readable error message. Example:
 125                                 "STATUS=Completed 66% of file system
 126                                 check..."</para></listitem>
 127                         </varlistentry>
 128
 129                         <varlistentry>
 130                                 <term>ERRNO=...</term>
 131
 132                                 <listitem><para>If a daemon fails, the
 133                                 errno-style error code, formatted as
 134                                 string. Example: "ERRNO=2" for
 135                                 ENOENT.</para></listitem>
 136                         </varlistentry>
 137
 138                         <varlistentry>
 139                                 <term>BUSERROR=...</term>
 140
 141                                 <listitem><para>If a daemon fails, the
 142                                 D-Bus error-style error code. Example:
 143                                 "BUSERROR=org.freedesktop.DBus.Error.TimedOut"</para></listitem>
 144                         </varlistentry>
 145
 146                         <varlistentry>
 147                                 <term>MAINPID=...</term>
 148
 149                                 <listitem><para>The main pid of the
 150                                 daemon, in case the init system did
 151                                 not fork off the process
 152                                 itself. Example:
 153                                 "MAINPID=4711"</para></listitem>
 154                         </varlistentry>
 155
 156                         <varlistentry>
 157                                 <term>WATCHDOG=1</term>
 158
 159                                 <listitem><para>Tells systemd to
 160                                 update the watchdog timestamp. This is
 161                                 the keep-alive ping that services need
 162                                 to issue in regular intervals if
 163                                 <varname>WatchdogSec=</varname> is
 164                                 enabled for it. See
 165                                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 166                                 for details. It is recommended to send
 167                                 this message if the
 168                                 <varname>$WATCHDOG_PID</varname>
 169                                 environment variable has been set to
 170                                 the PID of the service process, in
 171                                 every half the time interval that is
 172                                 specified in the
 173                                 <varname>$WATCHDOG_USEC</varname>
 174                                 environment variable. See
 175                                 <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 176                                 for details.</para></listitem>
 177                         </varlistentry>
 178                 </variablelist>
 179
 180                 <para>It is recommended to prefix variable names that
 181                 are not shown in the list above with
 182                 <varname>X_</varname> to avoid namespace
 183                 clashes.</para>
 184
 185                 <para>Note that systemd will accept status data sent
 186                 from a daemon only if the
 187                 <varname>NotifyAccess=</varname> option is correctly
 188                 set in the service definition file. See
 189                 <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 190                 for details.</para>
 191
 192                 <para><function>sd_notifyf()</function> is similar to
 193                 <function>sd_notify()</function> but takes a
 194                 <function>printf()</function>-like format string plus
 195                 arguments.</para>
 196         </refsect1>
 197
 198         <refsect1>
 199                 <title>Return Value</title>
 200
 201                 <para>On failure, these calls return a negative
 202                 errno-style error code. If
 203                 <varname>$NOTIFY_SOCKET</varname> was not set and
 204                 hence no status data could be sent, 0 is returned. If
 205                 the status was sent, these functions return with a
 206                 positive return value. In order to support both, init
 207                 systems that implement this scheme and those which
 208                 do not, it is generally recommended to ignore the return
 209                 value of this call.</para>
 210         </refsect1>
 211
 212         <refsect1>
 213                 <title>Notes</title>
 214
 215                 <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
 216
 217                 <para>Internally, these functions send a single
 218                 datagram with the state string as payload to the
 219                 <constant>AF_UNIX</constant> socket referenced in the
 220                 <varname>$NOTIFY_SOCKET</varname> environment
 221                 variable. If the first character of
 222                 <varname>$NOTIFY_SOCKET</varname> is <literal>@</literal>, the string is
 223                 understood as Linux abstract namespace socket. The
 224                 datagram is accompanied by the process credentials of
 225                 the sending daemon, using SCM_CREDENTIALS.</para>
 226         </refsect1>
 227
 228         <refsect1>
 229                 <title>Environment</title>
 230
 231                 <variablelist class='environment-variables'>
 232                         <varlistentry>
 233                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 234
 235                                 <listitem><para>Set by the init system
 236                                 for supervised processes for status
 237                                 and start-up completion
 238                                 notification. This environment variable
 239                                 specifies the socket
 240                                 <function>sd_notify()</function> talks
 241                                 to. See above for details.</para></listitem>
 242                         </varlistentry>
 243                 </variablelist>
 244         </refsect1>
 245
 246         <refsect1>
 247                 <title>Examples</title>
 248
 249                 <example>
 250                         <title>Start-up Notification</title>
 251
 252                         <para>When a daemon finished starting up, it
 253                         might issue the following call to notify
 254                         the init system:</para>
 255
 256                         <programlisting>sd_notify(0, "READY=1");</programlisting>
 257                 </example>
 258
 259                 <example>
 260                         <title>Extended Start-up Notification</title>
 261
 262                         <para>A daemon could send the following after
 263                         completing initialization:</para>
 264
 265                         <programlisting>sd_notifyf(0, "READY=1\n"
 266               "STATUS=Processing requests...\n"
 267               "MAINPID=%lu",
 268               (unsigned long) getpid());</programlisting>
 269                 </example>
 270
 271                 <example>
 272                         <title>Error Cause Notification</title>
 273
 274                         <para>A daemon could send the following shortly before exiting, on failure</para>
 275
 276                         <programlisting>sd_notifyf(0, "STATUS=Failed to start up: %s\n"
 277               "ERRNO=%i",
 278               strerror(errno),
 279               errno);</programlisting>
 280                 </example>
 281         </refsect1>
 282
 283         <refsect1>
 284                 <title>See Also</title>
 285                 <para>
 286                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 287                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 288                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 289                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 290                         <citerefentry><refentrytitle>sd_watchdog_enabled</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 291                 </para>
 292         </refsect1>
 293
 294 </refentry>