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<chapter>
  <header>
    <copyright>
      <year>2003</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>Releases</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>release_structure.xml</file>
  </header>
  <marker id="releases section"></marker>
  <p>This section is to be read with the <c>rel(4)</c>, <c>systools(3)</c>,
  and <c>script(4)</c> manual pages in SASL.</p>

  <section>
    <title>Release Concept</title>
    <p>When you have written one or more applications, you might want
      to create a complete system with these applications and a
      subset of the Erlang/OTP applications. This is called a
      <em>release</em>.</p>
    <p>To do this, create a
    <seeguide marker="#res_file">release resource file</seeguide> that
      defines which applications are included in the release.</p>
    <p>The release resource file is used to generate
      <seeguide marker="#boot">boot scripts</seeguide> and
      <seeguide marker="#pack">release packages</seeguide>. A system
      that is transferred to and installed at another site is called a
      <em>target system</em>. How to use a release package to create a
      target system is described in System Principles.</p>
  </section>

  <section>
    <marker id="res_file"></marker>
    <title>Release Resource File</title>
    <p>To define a release, create a <em>release resource file</em>,
      or in short a <c>.rel</c> file. In the file, specify the name and
      version of the release, which ERTS version it is based on,
      and which applications it consists of:</p>
    <code type="none">
{release, {Name,Vsn}, {erts, EVsn},
 [{Application1, AppVsn1},
   ...
  {ApplicationN, AppVsnN}]}.</code>
    <p><c>Name</c>, <c>Vsn</c>, <c>EVsn</c>, and <c>AppVsn</c> are
    strings.</p>
    <p>The file must be named <c>Rel.rel</c>, where <c>Rel</c> is a
      unique name.</p>
    <p>Each <c>Application</c> (atom) and <c>AppVsn</c> is
      the name and version of an application included in the release.
      The minimal release based on Erlang/OTP consists of
      the Kernel and STDLIB applications, so these
      applications must be included in the list.</p>
    <p>If the release is to be upgraded, it must also include
      the SASL application.</p>
    <marker id="ch_rel"></marker>
    <p><em>Example: </em> A release of <c>ch_app</c> from
      <seeguide marker="applications#ch_app">Applications</seeguide>
      has the following <c>.app</c> file:</p>
    <code type="none">
{application, ch_app,
 [{description, "Channel allocator"},
  {vsn, "1"},
  {modules, [ch_app, ch_sup, ch3]},
  {registered, [ch3]},
  {applications, [kernel, stdlib, sasl]},
  {mod, {ch_app,[]}}
 ]}.</code>
    <p>The <c>.rel</c> file must also contain <c>kernel</c>,
      <c>stdlib</c>, and <c>sasl</c>, as these applications are required
      by <c>ch_app</c>. The file is called <c>ch_rel-1.rel</c>:</p>
    <code type="none">
{release,
 {"ch_rel", "A"},
 {erts, "5.3"},
 [{kernel, "2.9"},
  {stdlib, "1.12"},
  {sasl, "1.10"},
  {ch_app, "1"}]
}.</code>
  </section>

  <section>
    <marker id="boot"></marker>
    <title>Generating Boot Scripts</title>
    <p><c>systools</c> in the SASL application includes tools to
      build and check releases. The functions read the <c>rel</c> and
      <c>.app</c> files and perform syntax and dependency checks.
      The <c>systools:make_script/1,2</c> function is used to generate
      a boot script (see System Principles):</p>
    <pre>
1> <input>systools:make_script("ch_rel-1", [local]).</input>
ok</pre>
    <p>This creates a boot script, both the readable version,
    <c>ch_rel-1.script</c>, and the binary version, <c>ch_rel-1.boot</c>,
    used by the runtime system.</p>
    <list type="bulleted">
      <item><c>"ch_rel-1"</c> is the name of the <c>.rel</c> file,
      minus the extension.</item>
      <item><c>local</c> is an option that means that the directories
      where the applications are found are used in the boot script,
      instead of <c>$ROOT/lib</c> (<c>$ROOT</c> is the root directory
      of the installed release).</item>
    </list>
    <p> This is a useful way to test a generated boot script locally.</p>
    <p>When starting Erlang/OTP using the boot script, all applications
    from the <c>.rel</c> file are automatically loaded and started:</p>
    <pre>
% <input>erl -boot ch_rel-1</input>
Erlang (BEAM) emulator version 5.3

Eshell V5.3  (abort with ^G)
1>
=PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
          supervisor: {local,sasl_safe_sup}
             started: [{pid,&lt;0.33.0>},
                       {name,alarm_handler},
                       {mfa,{alarm_handler,start_link,[]}},
                       {restart_type,permanent},
                       {shutdown,2000},
                       {child_type,worker}]

...

=PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
         application: sasl
          started_at: nonode@nohost

...
=PROGRESS REPORT==== 13-Jun-2003::12:01:15 ===
         application: ch_app
          started_at: nonode@nohost</pre>
  </section>

  <section>
    <marker id="pack"></marker>
    <title>Creating a Release Package</title>
    <p>The <c>systools:make_tar/1,2</c> function takes a <c>.rel</c> file
    as input and creates a zipped tar file with the code for the specified
    applications, a <em>release package</em>:</p>
    <pre>
1> <input>systools:make_script("ch_rel-1").</input>
ok
2> <input>systools:make_tar("ch_rel-1").</input>
ok</pre>
   <p>The release package by default contains:</p>
   <list type="bulleted">
     <item>The <c>.app</c> files</item>
     <item>The <c>.rel</c> file</item>
     <item>The object code for all applications, structured according
     to the
     <seeguide marker="applications#app_dir">application directory
     structure</seeguide></item>
     <item>The binary boot script renamed to <c>start.boot</c></item>
   </list>
    <pre>
% <input>tar tf ch_rel-1.tar</input>
lib/kernel-2.9/ebin/kernel.app
lib/kernel-2.9/ebin/application.beam
...
lib/stdlib-1.12/ebin/stdlib.app
lib/stdlib-1.12/ebin/beam_lib.beam
...
lib/sasl-1.10/ebin/sasl.app
lib/sasl-1.10/ebin/sasl.beam
...
lib/ch_app-1/ebin/ch_app.app
lib/ch_app-1/ebin/ch_app.beam
lib/ch_app-1/ebin/ch_sup.beam
lib/ch_app-1/ebin/ch3.beam
releases/A/start.boot
releases/A/ch_rel-1.rel
releases/ch_rel-1.rel</pre>
    <p>A new boot script was generated, without
      the <c>local</c> option set, before the release package was made.
      In the release package, all application directories are placed
      under <c>lib</c>. You do not know where the release package
      will be installed, so no hard-coded absolute paths are allowed.</p>
    <p>The release resource file <c>mysystem.rel</c> is duplicated in
      the tar file. Originally, this file was only stored in
      the <c>releases</c> directory to make it possible for
      the <c>release_handler</c> to extract this file
      separately. After unpacking the tar file, <c>release_handler</c>
      would automatically copy the file
      to <c>releases/FIRST</c>. However, sometimes the tar file is
      unpacked without involving the <c>release_handler</c> (for
      example, when unpacking the first target system) and the file
      is therefore now instead duplicated in the tar file so no manual
      copying is necessary.</p>
    <p>If a <c>relup</c> file and/or a system configuration file called
      <c>sys.config</c>, or a <c>sys.config.src</c>, is found, these files
      are also included in the release package. See
      <seeguide marker="release_handling#req">Release Handling</seeguide>.</p>
    <p>Options can be set to make the release package include source
      code and the ERTS binary as well.</p>
    <p>For information on how to install the first target system, using
      a release package, see System Principles. For information
      on how to install a new release package in an existing system, see
      <seeguide marker="release_handling">Release Handling</seeguide>.</p>
  </section>

  <section>
    <marker id="reldir"></marker>
    <title>Directory Structure</title>
    <p>The directory structure for the code installed by the release handler
      from a release package is as follows:</p>
    <code type="none">
$ROOT/lib/App1-AVsn1/ebin
                    /priv
         /App2-AVsn2/ebin
                    /priv
         ...
         /AppN-AVsnN/ebin
                    /priv
     /erts-EVsn/bin
     /releases/Vsn
     /bin</code>
     <list type="bulleted">
       <item><c>lib</c> - Application directories</item>
       <item><c>erts-EVsn/bin</c> - Erlang runtime system executables</item>
       <item><c>releases/Vsn</c> - <c>.rel</c> file and boot script
       <c>start.boot</c>; if present in the release package, <c>relup</c>
       and/or <c>sys.config</c> or <c>sys.config.src</c></item>
       <item><c>bin</c> - Top-level Erlang runtime system executables</item>
     </list>
    <p>Applications are not required to be located under directory
      <c>$ROOT/lib</c>. Several installation directories, which contain
      different parts of a system, can thus exist.
      For example, the previous example can be extended as follows:</p>
    <pre>
$SECOND_ROOT/.../SApp1-SAVsn1/ebin
                             /priv
                /SApp2-SAVsn2/ebin
                             /priv
                ...
                /SAppN-SAVsnN/ebin
                             /priv

$THIRD_ROOT/TApp1-TAVsn1/ebin
                        /priv
           /TApp2-TAVsn2/ebin
                        /priv
           ...
           /TAppN-TAVsnN/ebin
                        /priv</pre>
    <p><c>$SECOND_ROOT</c> and <c>$THIRD_ROOT</c> are introduced as
      <c>variables</c> in the call to the <c>systools:make_script/2</c>
      function.</p>

    <section>
      <title>Disk-Less and/or Read-Only Clients</title>
      <p>If a complete system consists of disk-less and/or
        read-only client nodes, a <c>clients</c> directory is to be
        added to the <c>$ROOT</c> directory. A read-only node is
        a node with a read-only file system.</p>
      <p>The <c>clients</c> directory is to have one subdirectory
        per supported client node. The name of each client directory
        is to be the name of the corresponding client node. As a
        minimum, each client directory is to contain the <c>bin</c> and
        <c>releases</c> subdirectories. These directories are used to
        store information about installed releases and to appoint the
        current release to the client. The <c>$ROOT</c>
        directory thus contains the following:</p>
      <code type="none">
$ROOT/...
    /clients/ClientName1/bin
                        /releases/Vsn
            /ClientName2/bin
                        /releases/Vsn
            ...
            /ClientNameN/bin
                        /releases/Vsn</code>
      <p>This structure is to be used if all clients are running
        the same type of Erlang machine. If there are clients running
        different types of Erlang machines, or on different operating
        systems, the <c>clients</c> directory can be divided into one
        subdirectory per type of Erlang machine. Alternatively, one
	<c>$ROOT</c> can be set up per type of machine. For each
        type, some of the directories specified for the <c>$ROOT</c>
        directory are to be included:</p>
      <code type="none">
$ROOT/...
    /clients/Type1/lib
                  /erts-EVsn
                  /bin
                  /ClientName1/bin
                              /releases/Vsn
                  /ClientName2/bin
                              /releases/Vsn
                  ...
                  /ClientNameN/bin
                              /releases/Vsn
            ...
            /TypeN/lib
                  /erts-EVsn
                  /bin
                  ...</code>
      <p>With this structure, the root directory for clients of
        <c>Type1</c> is <c>$ROOT/clients/Type1</c>.</p>
    </section>
  </section>
</chapter>
