path: root/system/doc/installation_guide/otp_version.xml

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<chapter>
  <header>
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      <year>2014</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
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      The contents of this file are subject to the Erlang Public License,
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    <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>