system/doc/installation_guide/otp_version.xml


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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>2014</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>OTP version</title>
    <prepared></prepared>
    <responsible></responsible>
    <docno></docno>
    <approved></approved>
    <checked></checked>
    <date>2014-02-19</date>
    <rev></rev>
    <file>otp_version.xml</file>
  </header>
    <p>As of OTP release 17, the OTP release number corresponds to
    the major OTP version number. In the normal case, the OTP version
    number will be constructed as
    <c>&lt;Major&gt;.&lt;Minor&gt;.&lt;Patch&gt;</c>. However more
    dot separated parts may exist. If all parts less significant than
    <c>Minor</c> equals <c>0</c>, they are omitted when printing the
    version. Release candidates have an <c>-rc&lt;N&gt;</c> suffix. The
    OTP version as a concept was introduced in OTP 17.</p>
    <p>OTP of a specific version is a set of applications of
    specific versions. The application versions identified by
    an OTP version corresponds to application versions that
    have been tested together by the Erlang/OTP team at Ericsson AB.
    An OTP system can however be put together with applications from
    different OTP versions. Such a combination of application versions
    has not been tested by the Erlang/OTP team. It is therefore
    <em>always preferred to use OTP applications from one single OTP
    version</em>.</p>
    <p>In an OTP source code tree as well as in an installed OTP
    development system, the OTP version can be read from the text
    file <c>OTP_VERSION</c> in the OTP installation root directory
    (<seealso marker="kernel:code#root_dir/0"><c>code:root_dir()</c></seealso>).</p>
    <p>If the version read from the <c>OTP_VERSION</c> file in a
    development system has a <c>**</c> suffix, the system has been
    patched using the <c>$ERL_TOP/otp_build patch_app</c> tool. In
    this case, the system consists of application versions from
    multiple OTP versions. The version preceding the <c>**</c>
    suffix corresponds to the OTP version of the base system that
    has been patched.</p>
    <p>On a target system (see the
    <seealso marker="doc/system_principles:create_target">system principles</seealso>
    documentation) no <c>OTP_VERSION</c> file will exist. This since
    one easily can create a target system where it is hard to even
    determine the base OTP version.</p>
    <p>Note that if a development system is updated by other means
    than <c>$ERL_TOP/otp_build patch_app</c>, the <c>OTP_VERSION</c>
    file may identify wrong OTP version.</p>
</chapter>