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  <header>
    <copyright>
      <year>1997</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>appup</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
  </header>
  <file>appup</file>
  <filesummary>Application upgrade file.</filesummary>
  <description>
    <p>The <em>application upgrade file</em> defines how an application
      is upgraded or downgraded in a running system.</p>
    <p>This file is used by the functions in <c>systools</c> when
      generating a release upgrade file <c>relup</c>.</p>
  </description>

  <section>
    <title>FILE SYNTAX</title>
    <p>The application upgrade file should be called
      <c>Application.appup</c> where <c>Application</c> is the name of
      the application.  The file should be located in the <c>ebin</c>
      directory for the application.</p>
    <p>The <c>.appup</c> file contains one single Erlang term, which
      defines the instructions used to upgrade or downgrade
      the application.  The file has the following syntax:</p>
    <code type="none">
{Vsn,
  [{UpFromVsn, Instructions}, ...],
  [{DownToVsn, Instructions}, ...]}.
    </code>
    <list type="bulleted">
      <item>
        <p><c>Vsn = string()</c> is the current version of
          the application.</p>
      </item>
      <item>
        <p><c>UpFromVsn = string()</c> is an earlier version of
          the application to upgrade from.</p>
      </item>
      <item>
        <p><c>DownToVsn = string()</c> is an earlier version of
          the application to downgrade to.</p>
      </item>
      <item>
        <p><c>Instructions</c> is a list of <em>release upgrade instructions</em>, see below. It is recommended to use
          high-level instructions only. These are automatically
          translated to low-level instructions by <c>systools</c> when
          creating the <c>relup</c> file.</p>
      </item>
    </list>
  </section>

  <section>
    <title>RELEASE UPGRADE INSTRUCTIONS</title>
    <p>Release upgrade instructions are interpreted by the release
      handler when an upgrade or downgrade is made. For more
      information about release handling, refer to <em>OTP Design Principles</em>.</p>
    <p>A process is said to <em>use</em> a module <c>Mod</c>, if
      <c>Mod</c> is listed in the <c>Modules</c> part of the child
      specification used to start the process, see <c>supervisor(3)</c>.
      In the case of gen_event, an event manager process is said to use
      <c>Mod</c> if <c>Mod</c> is an installed event handler.</p>
    <p><em>High-level instructions</em></p>
    <pre>
{update, Mod}
{update, Mod, supervisor}
{update, Mod, Change}
{update, Mod, DepMods}
{update, Mod, Change, DepMods}
{update, Mod, Change, PrePurge, PostPurge, DepMods}
{update, Mod, Timeout, Change, PrePurge, PostPurge, DepMods}
{update, Mod, ModType, Timeout, Change, PrePurge, PostPurge, DepMods}
  Mod = atom()
  ModType = static | dynamic
  Timeout = int()>0 | default | infinity
  Change = soft | {advanced,Extra}
    Extra = term()
  PrePurge = PostPurge = soft_purge | brutal_purge
  DepMods = [Mod]
    </pre>
    <p>Synchronized code replacement of processes using the module
      <c>Mod</c>. All those processes are suspended using
      <c>sys:suspend</c>, the new version of the module is loaded and
      then the processes are resumed using <c>sys:resume</c>.</p>
    <p><c>Change</c> defaults to <c>soft</c> and defines the type of
      code change. If it is set to <c>{advanced,Extra}</c>, processes
      implemented using gen_server, gen_fsm or gen_event will transform
      their internal state by calling the callback function
      <c>code_change</c>. Special processes will call the callback
      function <c>system_code_change/4</c>. In both cases, the term
      <c>Extra</c> is passed as an argument to the callback function.</p>
    <p><c>PrePurge</c> defaults to <c>brutal_purge</c> and controls
      what action to take with processes that are executing old code
      before loading the new version of the module. If the value
      is <c>brutal_purge</c>, the processes are killed. If the value is
      <c>soft_purge</c>, <c>release_handler:install_release/1</c>
      returns <c>{error,{old_processes,Mod}}</c>.</p>
    <p><c>PostPurge</c> defaults to <c>brutal_purge</c> and controls
      what action to take with processes that are executing old code
      when the new version of the module has been loaded. If the value
      is <c>brutal_purge</c>, the code is purged when the release is
      made permanent and the processes are killed. If the value is
      <c>soft_purge</c>, the release handler will purge the old code
      when no remaining processes execute the code.</p>
    <p><c>DepMods</c> defaults to [] and defines which other modules
      <c>Mod</c> is dependent on. In <c>relup</c>, instructions for
      suspending processes using <c>Mod</c> will come before
      instructions for suspending processes using modules in
      <c>DepMods</c> when upgrading, and vice versa when downgrading.
      In case of circular dependencies, the order of the instructions in
      the <c>appup</c> script is kept.</p>
    <p><c>Timeout</c> defines the timeout when suspending processes.
      If no value or <c>default</c> is given, the default value for
      <c>sys:suspend</c> is used.</p>
    <p><c>ModType</c> defaults to <c>dynamic</c> and specifies if
      the code is "dynamic", that is if a process using the module does
      spontaneously switch to new code, or if it is "static".
      When doing an advanced update and upgrading, the new version of a
      dynamic module is loaded before the process is asked to change
      code. When downgrading, the process is asked to change code before
      loading the new version. For static modules, the new version is
      loaded before the process is asked to change code, both in
      the case of upgrading and downgrading. Callback modules are
      dynamic.</p>
    <p><c>update</c> with argument <c>supervisor</c> is used when
      changing the start specification of a supervisor.</p>
    <pre>
{load_module, Mod}
{load_module, Mod, DepMods}
{load_module, Mod, PrePurge, PostPurge, DepMods}
  Mod = atom()
  PrePurge = PostPurge = soft_purge | brutal_purge
  DepMods = [Mod]
    </pre>
    <p>Simple code replacement of the module <c>Mod</c>.</p>
    <p>See <c>update</c> above for a description of <c>PrePurge</c> and
      <c>PostPurge</c>.</p>
    <p><c>DepMods</c> defaults to [] and defines which other modules
      <c>Mod</c> is dependent on. In <c>relup</c>, instructions for
      loading these modules will come before the instruction for loading
      <c>Mod</c> when upgrading, and vice versa when downgrading.</p>
    <pre>
{add_module, Mod}
  Mod = atom()
    </pre>
    <p>Loads a new module <c>Mod</c>.</p>
    <pre>
{delete_module, Mod}
  Mod = atom()
    </pre>
    <p>Deletes a module <c>Mod</c> using the low-level instructions
      <c>remove</c> and <c>purge</c>.</p>
    <pre>
{add_application, Application}
  Application = atom()
    </pre>
    <p>Adding an application means that the modules defined by
      the <c>modules</c> key in the <c>.app</c> file are loaded using
      <c>add_module</c>, then the application is started.</p>
    <pre>
{remove_application, Application}
  Application = atom()
    </pre>
    <p>Removing an application means that the application is stopped,
      the modules are unloaded using <c>delete_module</c> and then
      the application specification is unloaded from the application
      controller.</p>
    <pre>
{restart_application, Application}
  Application = atom()
    </pre>
    <p>Restarting an application means that the application is
      stopped and then started again similar to using the instructions
      <c>remove_application</c> and <c>add_application</c> in sequence.</p>
    <p><em>Low-level instructions</em></p>
    <pre>
{load_object_code, {App, Vsn, [Mod]}}
  App = Mod = atom()
  Vsn = string()
    </pre>
    <p>Reads each <c>Mod</c> from the directory <c>App-Vsn/ebin</c> as
      a binary. It does not load the modules. The instruction should be
      placed first in the script in order to read all new code from file
      to make the suspend-load-resume cycle less time consuming. After
      this instruction has been executed, the code server with the new
      version of <c>App</c>.</p>
    <pre>
point_of_no_return
    </pre>
    <p>If a crash occurs after this instruction, the system cannot
      recover and is restarted from the old version of the release.
      The instruction must only occur once in a script. It should be
      placed after all <c>load_object_code</c> instructions.</p>
    <pre>
{load, {Mod, PrePurge, PostPurge}}
  Mod = atom()
  PrePurge = PostPurge = soft_purge | brutal_purge
    </pre>
    <p>Before this instruction occurs, <c>Mod</c> must have been loaded
      using <c>load_object_code</c>. This instruction loads the module.
      <c>PrePurge</c> is ignored. See the high-level instruction
      <c>update</c> for a description of <c>PostPurge</c>.</p>
    <pre>
{remove, {Mod, PrePurge, PostPurge}}
  Mod = atom()
  PrePurge = PostPurge = soft_purge | brutal_purge
    </pre>
    <p>Makes the current version of <c>Mod</c> old.
      <c>PrePurge</c> is ignored. See the high-level instruction
      <c>update</c> for a description of <c>PostPurge</c>.</p>
    <pre>
{purge, [Mod]}
  Mod = atom()
    </pre>
    <p>Purges each module <c>Mod</c>, that is removes the old code.
      Note that any process executing purged code is killed.</p>
    <pre>
{suspend, [Mod | {Mod, Timeout}]}
  Mod = atom()
  Timeout = int()>0 | default | infinity
    </pre>
    <p>Tries to suspend all processes using a module <c>Mod</c>. If a
      process does not respond, it is ignored. This may cause
      the process to die, either because it crashes when it
      spontaneously switches to new code, or as a result of a purge
      operation. If no <c>Timeout</c> is specified or <c>default</c> is
      given, the default value for <c>sys:suspend</c> is used.</p>
    <pre>
{resume, [Mod]}
  Mod = atom()
    </pre>
    <p>Resumes all suspended processes using a module <c>Mod</c>.</p>
    <pre>
{code_change, [{Mod, Extra}]}
{code_change, Mode, [{Mod, Extra}]}
  Mod = atom()
  Mode = up | down
  Extra = term()
    </pre>
    <p><c>Mode</c> defaults to <c>up</c> and specifies if it is an
      upgrade or downgrade.</p>
    <p>This instruction sends a <c>code_change</c> system message to
      all processes using a module <c>Mod</c> by calling the function
      <c>sys:change_code</c>, passing the term <c>Extra</c> as argument.</p>
    <pre>
{stop, [Mod]}
  Mod = atom()
    </pre>
    <p>Stops all processes using a module <c>Mod</c> by calling
      <c>supervisor:terminate_child/2</c>. The instruction is useful
      when the simplest way to change code is to stop and restart the
      processes which run the code.</p>
    <pre>
{start, [Mod]}
  Mod = atom()
    </pre>
    <p>Starts all stopped processes using a module <c>Mod</c> by calling
      <c>supervisor:restart_child/2</c>.</p>
    <pre>
{sync_nodes, Id, [Node]}
{sync_nodes, Id, {M, F, A}}
  Id = term()
  Node = node()
  M = F = atom()
  A = [term()]
    </pre>
    <p><c>apply(M, F, A)</c> must return a list of nodes.</p>
    <p>The instruction synchronizes the release installation with other
      nodes. Each <c>Node</c> must evaluate this command, with the same
      <c>Id</c>. The local node waits for all other nodes to evaluate
      the instruction before execution continues. In case a node goes
      down, it is considered to be an unrecoverable error, and
      the local node is restarted from the old release. There is no
      timeout for this instruction, which means that it may hang
      forever.</p>
    <pre>
{apply, {M, F, A}}
  M = F = atom()
  A = [term()]
    </pre>
    <p>Evaluates <c>apply(M, F, A)</c>. If the instruction appears
      before the <c>point_of_no_return</c> instruction, a failure is
      caught. <c>release_handler:install_release/1</c> then returns
      <c>{error,{'EXIT',Reason}}</c>, unless <c>{error,Error}</c> is
      thrown or returned. Then it returns <c>{error,Error}</c>.</p>
    <p>If the instruction appears after the <c>point_of_no_return</c>
      instruction, and the function call fails, the system is
      restarted.</p>
    <pre>
restart_new_emulator
    </pre>
    <p>Shuts down the current emulator and starts a ne one. All
      processes are terminated gracefully. The new release must still
      be made permanent when the new emulator is up and running.
      Otherwise, the old emulator is started in case of a emulator
      restart. This instruction should be used when a new emulator is
      introduced, or if a complete reboot of the system should be done.</p>
  </section>

  <section>
    <title>SEE ALSO</title>
    <p><seealso marker="relup">relup(4)</seealso>,
      <seealso marker="release_handler">release_handler(3)</seealso>,
      supervisor(3),
      <seealso marker="systools">systools(3)</seealso></p>
  </section>
</fileref>

