Doc updates to install, migration, and after migration sections

doc/adoc/user_guide.adoc

@@ -92,6 +92,13 @@ If your system is not configured for it, it is recommended that at least
 one of the users on the system has a `~/.ssh/authorized_keys` file with a
 private key accessible by the person executing the system upgrade.
 
+Requirement for root filesystem::
+Root "/" and all core OS functional folders such as /var, /etc, /usr must
+be on a single partition. Multiple partition support, such as LVM, is limited
+to configurations where the separated partitions do not contain OS critical
+data or processes. For example, DMS will function if /home is its own
+partition, but not if /var is on a separate partition from root.
+
 == Upgrade Pre-Checks
 The suse-migration-pre-checks package contains the `suse-migration-pre-checks`
 script that checks for possible incompatibilities when doing a migration.
@@ -138,19 +145,16 @@ For data center customers it is recommended to continue to use the
 documented offline distribution upgrade using the next distribution
 version installation media.
 
-To install the distribution migration system run:
-
-[listing]
-tux > sudo zypper in SLES15-Migration
-
 The distribution migration process can be invoked using different methods.
 One method of activating the migration is the `run_migration` included with
 the SLES15-Migration package. The second method to invoking the migration
 process is via reboot after installing the suse-migration-sle15-activation
 package.
 
+Option 1 - Trigger via run_migration::
+
 [listing]
-tux > sudo zypper in suse-migration-sle15-activation
+tux > sudo zypper in SLES15-Migration
 
 The `run_migration` uses `kexec` to boot into the kernel delivered with the
 upgrade image delivered by the SLES15-Migration package. Once this system
@@ -159,6 +163,19 @@ started. However, `kexec` is not supported and does not function in certain
 conditions. The `run_migration` utility does not work in Xen based
 environments.
 
+If kexec causes a kernel panic this can cause the system to hang and the 
+distribution migration to fail. In that case refer to this TID:
+https://www.suse.com/support/kb/doc/?id=000019733
+And set the "soft_reboot" customization option:
+
+[listing]
+echo "soft_reboot: false" >> /etc/sle-migration-service.yml
+
+Option 2 - Trigger via reboot::
+
+[listing]
+tux > sudo zypper in SLES15-Migration suse-migration-sle15-activation
+
 Starting the migration via reboot after installing the
 suse-migration-sle15-activation package covers the Xen use case but does
 not work in cases where there is no direct access to the root file system
@@ -284,19 +301,25 @@ independent initrd can be created by setting
 build_host_independent_initrd: true|false
 
 == Run the Migration
+Migration can be triggered either via run_migration or via reboot.
+
+Option 1 - Running Migration via run_migration::
 After the install of the `SLES15-Migration` package, start the migration
-by calling the following command:
+process by calling the following command:
 
 [listing]
 tux > sudo run_migration
 
+Option 2 - Running Migration via reboot::
 [NOTE]
-If the `suse-migration-sle15-activation` package was installed,
-start the migration by a reboot of the system as follows:
+If using the `reboot` method and install option was used,
+reboot system:
 
 [listing]
 tux > sudo reboot
 
+After Migration has been triggered via either method::
+[NOTE]
 After the upgrade has started, the only way to access the system during the
 upgrade process is via ssh with a user called `migration`:
 
@@ -314,6 +337,13 @@ Whether the upgrade succeeded or not, a log file is available in
 upgrade process. If the upgrade failed, the file `/etc/issue` will contain
 a pointer to the respective log file.
 
+In addition, the distribution migration RPM packages `SLES15-Migration`
+and `suse-migration-sle15-activation` will be removed.
+This is to prevent the migration from being run multiple times and causing
+a failure loop.
+To start the migration again, the RPMs will need to be reinstalled following
+the commands from the Installation Section of this document.
+
 == Caveats and Unsupported Conditions
 * Configuration files that have been modified in the original system will
   not be overwritten by the upgrade process. The new version of the respective