path: root/erts/doc/src/epmd.xml

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  <header>
    <copyright>
      <year>1996</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.
    
      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.
    
    </legalnotice>

    <title>epmd</title>
    <prepared>Claes Wikstr&ouml;m</prepared>    
    <responsible></responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>98-01-05</date>
    <rev>A</rev>
    <file>epmd.xml</file>
  </header>
  <com>epmd</com>
  <comsummary>Erlang Port Mapper Daemon </comsummary>
  <description>
    <p>This daemon acts as a name server on all hosts  involved  in
      distributed  Erlang computations. When an Erlang node 
      starts, the node has a name and it obtains an address from the host 
      OS kernel.
      The name and the address are sent to the
      <c><![CDATA[epmd]]></c> daemon running on the local host.
      In a TCP/IP environment, the address consists
      of the IP address and a port number. The name of the node is
      an atom on the form of <c><![CDATA[Name@Node]]></c>.
      The job of the <c><![CDATA[epmd]]></c> daemon is to keep track of which
      node name listens on which address. Hence, <c><![CDATA[epmd]]></c> map
      symbolic node names to machine addresses.</p>
    <p>The daemon is started automatically by the Erlang start-up script.</p>
    <p>The program <c><![CDATA[epmd]]></c> can also be used for a variety of other 
      purposes, for example checking the DNS (Domain Name System) 
      configuration of a host.</p>
  </description>
  <funcs>
    <func>
      <name>epmd [-daemon] </name>
      <fsummary>Start a name server as a daemon</fsummary>
      <desc>
        <p>Starts a name server as a daemon. If it has no argument, the
          <c><![CDATA[epmd]]></c> runs as a normal program with the controlling terminal 
          of the shell in which it is started. Normally, it should run as a 
          daemon.</p>
      </desc>
    </func>
    <func>
      <name>epmd -names</name>
      <fsummary>Request the names of the registered Erlang nodes on  this host</fsummary>
      <desc>
        <p>Requests the names of the local Erlang nodes <c><![CDATA[epmd]]></c> has 
          registered.</p>
      </desc>
    </func>
    <func>
      <name>epmd -kill</name>
      <fsummary>Kill the <c><![CDATA[epmd]]></c>process</fsummary>
      <desc>
        <p>Kills the <c><![CDATA[epmd]]></c> process.</p>
      </desc>
    </func>
    <func>
      <name>epmd -help</name>
      <fsummary>List options</fsummary>
      <desc>
        <p>Write short info about the usage including some debugging
          options not listed here.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="environment_variables"></marker>
    <title>Environment variables</title>
    <taglist>
      <tag><c><![CDATA[ERL_EPMD_PORT]]></c></tag>
      <item>
        <p>This environment variable can contain the port number epmd will use.
          The default port will work fine in most cases. A different port can
          be specified to allow several instances of epmd, representing
          independent clusters of nodes, to co-exist on the same host.
          All nodes in a cluster must use the same epmd port number.</p>
      </item>
    </taglist>
  </section>

  <section>
    <title>Logging</title>
    <p>On some operating systems <em>syslog</em> will be used for
      error reporting when epmd runs as an daemon. To enable
      the error logging you have to edit <path unix="" windows="">/etc/syslog.conf</path>
      file and add an entry</p>
    <code type="none"><![CDATA[
      !epmd
      *.*<TABs>/var/log/epmd.log
    ]]></code>
    <p>where &lt;TABs&gt; are at least one real tab character. Spaces will
      silently be ignored.
      </p>
  </section>
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