What is the adequate process to upgrade and migrate to RTC 4.0.5

Nicolas, you can find detailed steps for work you need to do here: https://pic.dhe.ibm.com/infocenter/clmhelp/v4r0m5/nav/0_6 . Also always look into the upgrade tips on the new version e.g. here: https://jazz.net/downloads/rational-team-concert/releases/4.0.5?p=upgrading

I have not done this myself, but you have 3 possible scenarios.

Scenario 1:

1. Migrate to the new OS (and database?)
   
2. Upgrade to the new version

Scenario 2:

1. Upgrade to the new version
2. Migrate to the new OS (and database?)

Scenario 3:

1. Upgrade to the new version and migrate to the new OS (and database?) in 1 step
   

Scenario 3 would be the most complex and depends on the migration tools copying the required configuration data over for you. You would have to make sure to include and copy data that does not get copied over automatically (such as the index files)  manually over. You would also have to manually edit the configuration files e.g. to point to the locations of the index files.

You would also have to make sure to rename the host name of the new machine to the host name of the old machine before turning on the new machine (and deactivating or changing the name of the old host) to keep your public URI stable.

For the 2 other scenarios, you would want to look into https://jazz.net/wiki/bin/view/Deployment/BackupCLM and do a backup of your configuration on the old machine and restore it on the new one. If you don't change the database, you would have to backup all other data and restore it. If you change the database server as well, you would have to change the configuration files to point to the new one. If you change the DB vendor you want to look up how to do that in the help.

I think Scenarios 1 and 2 are less complex, because you can test after each step.

I would suggest to test your migration and upgrade in an isolated test environment, before you do the production upgrade.

I hope this helps a bit.