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<comref>
  <header>
    <copyright>
      <year>1999</year><year>2021</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>run_erl</title>
    <prepared>Kent Boortz</prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date>1999-12-15</date>
    <rev></rev>
    <file>run_erl.xml</file>
  </header>
  <com>run_erl</com>
  <comsummary>Redirect Erlang input and output streams on Unix systems.</comsummary>
  <description>
    <p>The <c><![CDATA[run_erl]]></c> program is specific to Unix systems.
      This program redirects the standard input and standard
      output streams so that all output can be logged. It also lets the
      program <c><![CDATA[to_erl]]></c> connect to the Erlang console, making
      it possible to monitor and debug an embedded system remotely.</p>

    <p>For more information about the use, see the
      <seeguide marker="system/embedded:embedded_solaris">
      Embedded System User's Guide</seeguide> in System Documentation.</p>
  </description>

  <funcs>
    <func>
      <name>run_erl [-daemon] pipe_dir/ log_dir "exec command
        arg1 arg2 ..."</name>
      <fsummary>Start the Erlang emulator without attached terminal.</fsummary>
      <desc>
        <p>Arguments:</p>
        <taglist>
          <tag><c>-daemon</c></tag>
          <item>
            <p>This option is highly recommended. It makes <c>run_erl</c> run
              in the background completely detached from any controlling
              terminal and the command returns to the caller immediately.
              Without this option, <c>run_erl</c> must be started using several
              tricks in the shell to detach it completely from the
              terminal in use when starting it. The option must be the
              first argument to <c>run_erl</c> on the command line.</p>
          </item>
          <tag><c>pipe_dir</c></tag>
          <item>
            <p>The named pipe, usually <c><![CDATA[/tmp/]]></c>. It must be
              suffixed by a <c><![CDATA[/]]></c> (slash), that is,
              <c><![CDATA[/tmp/epipes/]]></c>, not
              <c><![CDATA[/tmp/epipes]]></c>.</p>
          </item>
          <tag><c>log_dir</c></tag>
          <item>
            <p>The log files, that is:</p>
            <list type="bulleted">
              <item>
                <p>One log file, <c><![CDATA[run_erl.log]]></c>, which logs
                  progress and warnings from the <c><![CDATA[run_erl]]></c>
                  program itself.</p>
              </item>
              <item>
                <p>Up to five log files at maximum 100 KB each with the content
                  of the standard streams from and to the command. (Both the
                  number of logs and sizes can be changed by environment
                  variables, see section <seecom
                  marker="#environment_variables">Environment Variables</seecom>
                  below.)</p>
                <p>When the logs are full, <c><![CDATA[run_erl]]></c> deletes
                  and reuses the oldest log file.</p>
              </item>
            </list>
          </item>
          <tag><c>"exec command arg1 arg2 ..."</c></tag>
          <item>
	    <p>A space-separated string specifying the program to be executed.
	      The second field is typically a command name such as <c>erl</c>.</p>
          </item>
        </taglist>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Notes concerning the Log Files</title>
    <p>While running, <c>run_erl</c> sends all output,
      uninterpreted, to a log file. The file is named
      <c><![CDATA[erlang.log.N]]></c>, where <c>N</c> is an integer. When the
      log is "full" (default log size is 100 KB), <c>run_erl</c> starts to log
      in file <c><![CDATA[erlang.log.(N+1)]]></c>, until <c>N</c> reaches a
      certain number (default 5), whereupon <c>N</c> starts at 1 again and
      the oldest files start getting overwritten.</p>

    <p>If no output comes from the Erlang shell, but
      the Erlang machine still seems to be alive, an "ALIVE" message is
      written to the log; it is a time stamp and is written, by default,
      after 15 minutes of inactivity. Also, if output from Erlang is
      logged, but more than 5 minutes (default) has passed since last time
      we got anything from Erlang, a time stamp is written in the
      log. The "ALIVE" messages look as follows:</p>

    <code type="none"><![CDATA[
===== ALIVE <date-time-string>    ]]></code>

    <p>The other time stamps look as follows:</p>

    <code type="none"><![CDATA[
===== <date-time-string>    ]]></code>

    <p><c><![CDATA[date-time-string]]></c> is the date and time the message is
      written, default in local time (can be changed to UTC if needed).
      It is formatted with the ANSI-C function <c><![CDATA[strftime]]></c>
      using the format string <c><![CDATA[%a %b %e %T %Z %Y]]></c>, which
      produces messages like
      <c><![CDATA[===== ALIVE Thu May 15 10:13:36 MEST 2003]]></c>; this can
      be changed, see the next section.</p>
  </section>

  <section>
    <marker id="environment_variables"/>
    <title>Environment Variables</title>
    <p>The following environment variables are recognized by <c>run_erl</c>
      and change the logging behavior. For more information, see the previous
      section.</p>

    <taglist>
      <tag><c>RUN_ERL_LOG_ALIVE_MINUTES</c></tag>
      <item>
        <p>How long to wait for output (in minutes) before writing an
          "ALIVE" message to the log. Defaults to 15, minimum is 1.</p>
      </item>
      <tag><c>RUN_ERL_LOG_ACTIVITY_MINUTES</c></tag>
      <item>
        <p>How long Erlang needs to be inactive before output is
          preceded with a time stamp. Defaults to
          <c>RUN_ERL_LOG_ALIVE_MINUTES div 3</c>, minimum is 1.</p>
      </item>
      <tag><c>RUN_ERL_LOG_ALIVE_FORMAT</c></tag>
      <item>
        <p>Specifies another format string to be used in the <c>strftime</c>
          C library call. That is, specifying this to
          <c><![CDATA["%e-%b-%Y, %T %Z"]]></c> gives
          log messages with time stamps like
          <c><![CDATA[15-May-2003, 10:23:04 MET]]></c>. For more information,
          see the documentation for the C library function <c>strftime</c>.
          Defaults to <c><![CDATA["%a %b %e %T %Z %Y"]]></c>.</p>
      </item>
      <tag><c>RUN_ERL_LOG_ALIVE_IN_UTC</c></tag>
      <item>
        <p>If set to anything else than <c>0</c>, it makes all
          times displayed by <c>run_erl</c> to be in UTC (GMT, CET, MET,
          without Daylight Saving Time), rather than in local time.
          This does not affect data coming from Erlang,
          only the logs output directly by <c>run_erl</c>. Application
          SASL can be modified accordingly by setting the Erlang
          application variable <c><![CDATA[utc_log]]></c> to
          <c><![CDATA[true]]></c>.</p>
      </item>
      <tag><c>RUN_ERL_LOG_GENERATIONS</c></tag>
      <item>
        <p>Controls the number of log files written before older
          files are reused. Defaults to 5, minimum is 2, maximum is 1000.</p>
	<p>Note that, as a way to indicate the newest file, <c>run_erl</c> will
	delete the oldest log file to maintain a "hole" in the file
	sequences. For example, if log files #1, #2, #4 and #5 exists, that
	means #2 is the latest and #4 is the oldest. You will therefore at most
	get one less log file than the value set by
	<c>RUN_ERL_LOG_GENERATIONS</c>.</p>
      </item>
      <tag><c>RUN_ERL_LOG_MAXSIZE</c></tag>
      <item>
        <p>The size, in bytes, of a log file before switching to a
          new log file. Defaults to 100000, minimum is 1000, maximum is
          about 2^30.</p>
      </item>
      <tag><c>RUN_ERL_DISABLE_FLOWCNTRL</c></tag>
      <item>
        <p>If defined, disables input and output flow control for the pty
          opend by <c>run_erl</c>. Useful if you want to remove any risk of
          accidentally blocking the flow control by using Ctrl-S (instead of
          Ctrl-D to detach), which can result in blocking of the entire Beam
          process, and in the case of running heart as supervisor even the
          heart process becomes blocked when writing log message to terminal,
          leaving the heart process unable to do its work.</p>
      </item>
    </taglist>
  </section>

  <section>
    <title>See Also</title>
    <p><seecom marker="start"><c>start(1)</c></seecom>,
      <seecom marker="start_erl"><c>start_erl(1)</c></seecom></p>
  </section>
</comref>
