Added postgresql update fix.

modules/ROOT/pages/index.adoc

@@ -45,6 +45,52 @@ Before you start the process you should use `df -h` to check the root file syste
 
 If you use postgresql, please note that the major version has increased from 16.9 to 18.0. This means that the database tables need to be adapted.
 
+[CAUTION]
+==== 
+The update will break Postgresql runtime and requires extra effort! 
+====
+
+Fedora 43 updates Postgresql from version 16 directly to version 18, skipping one major version. However, the update utility cannot process data from version 16. Therefore, perform the following steps:
+
+1. Verify that Postgresql failed to start and perform a backup.
++
+[source]
+----
+[…]$ systemctl status postgresql
+[…]$ sudo tar -cvJf /var/lib/pgsql/backups/postgres16-bak.tzx  /var/lib/pgsql/data/ 
+----
+2. Replace installed version 18 by version 17 und use it to update your database
++
+[source]
+----
+[…]$ sudo dnf install postgresql17-server postgresql17-upgrade --allowerasing 
+[…]$ sudo -u postgres postgresql-upgrade /var/lib/pgsql/data
+----
+3. Stop postgres and activate checksums which is a new default in version 18
++
+[source]
+----
+[…]$ systemctl stop postgresql
+[…]$ sudo -u postgres pg_checksums -D /var/lib/pgsql/data -e -P 
+----
+4. Reinstall version 18 and update the data again
++
+[source]
+----
+[…]$ mv /var/lib/pgsql/data_old  /var/lib/pgsql/data_old_16
+[…]$ sudo dnf install postgresql-server postgresql-upgrade --allowerasing
+[…]$ sudo -u postgres postgresql-upgrade /var/lib/pgsql/data
+----
+5. Start postgresql und check if everything works again
++
+[source]
+----
+[…]$ sudo systemctl start postgresql
+[…]$ sudo systemctl status postgresql
+----
+6. Execute the maintenance steps as recommended by the update program and fix collation issues if exist.
+7. Done
+
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