Document upgrade instructions restart_new_emulator and restart_emulator

1 files changed, 44 insertions, 8 deletions

diff --git a/system/doc/design_principles/release_handling.xml b/system/doc/design_principles/release_handling.xml
index 1d62c242c0..8ed36f3c56 100644
--- a/system/doc/design_principles/release_handling.xml
+++ b/system/doc/design_principles/release_handling.xml
@@ -4,7 +4,7 @@
 <chapter>
   <header>
     <copyright>
-      <year>2003</year><year>2009</year>
+      <year>2003</year><year>2011</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -313,18 +313,35 @@
     </section>
 
     <section>
+      <marker id="restart_new_emulator_instr"></marker>
       <title>restart_new_emulator (low-level)</title>
       <p>This instruction is used when changing to a new emulator
-        version, or if a system reboot is needed for some other reason.
-        Requires that the system is started with heart beat
+        version, or when any of the core applications kernel, stdlib
+        or sasl is upgraded. If a system reboot is needed for some
+        other reason, the <c>restart_emulator</c> instruction should
+        be used instead.</p>
+      <p>Requires that the system is started with heart beat
         monitoring, see <c>erl(1)</c> and <c>heart(3)</c>.</p>
-      <p>When the release handler encounters the instruction, it shuts
-        down the current emulator by calling <c>init:reboot()</c>, see
+      <p>The <c>restart_new_emulator</c> instruction shall always be
+        the very first instruction in a relup. If the relup is
+        generated by <c>systools:make_relup/3,4</c> this is
+        automatically ensured.</p>
+      <p>When the release handler encounters the instruction, it first
+        generates a temporary boot file, which starts the new versions
+        of the emulator and the core applications. Then it shuts down
+        the current emulator by calling <c>init:reboot()</c>, see
         <c>init(3)</c>. All processes are terminated gracefully and
         the system can then be rebooted by the heart program, using
-        the new release version. This new version must still be made
-        permanent when the new emulator is up and running. Otherwise,
-        the old version is used in case of a new system reboot.</p>
+        the temporary boot file. After the reboot, the rest of the
+        relup instructions are executed. This is done as a part of the
+        boot script.</p>
+      <p>An info report is written when the upgrade is completed. To
+        programatically find out if the upgrade is complete,
+        call <c>release_handler:which_releases/0</c> and check if the
+        expected release has status <c>current</c>.</p>
+      <p>The new version must be made permanent when the new emulator
+        is up and running. Otherwise, the old version will be used in
+        case of a new system reboot.</p>
       <p>On UNIX, the release handler tells the heart program which
         command to use to reboot the system. Note that the environment
         variable <c>HEART_COMMAND</c>, normally used by the heart
@@ -333,6 +350,25 @@
         by using the SASL configuration parameter <c>start_prg</c>, see
         <c>sasl(6)</c>.</p>
     </section>
+
+    <section>
+      <marker id="restart_emulator_instr"></marker>
+      <title>restart_emulator (low-level)</title>
+      <p>This instruction is not related to upgrades of erts or any of
+        the core applications. It can be used by any application to
+        force a restart of the emulator after all upgrade instructions
+        are executed.</p>
+      <p>There can only be one <c>restart_emulator</c> instruction in
+	a relup script, and it shall always be placed at the end. If
+	the relup is generated by <c>systools:make_relup/3,4</c> this
+	is automatically ensured.</p>
+      <p>When the release handler encounters the instruction, it shuts down
+        the emulator by calling <c>init:reboot()</c>, see
+        <c>init(3)</c>. All processes are terminated gracefully and
+        the system can then be rebooted by the heart program using the
+        new release version. No more upgrade instruction will be
+        executed after the restart.</p>
+    </section>
   </section>
 
   <section>