This is for those whose have problem migrating.
I migrated from Debian 7 to Debian 9, new server
I wanted to use the OST 1.7 but I could never had 1.7 work on the new Debian because of PHP 7 (Coming from PHP 5.3 I got from Apache error 500)
I decided to upgrade Osticket 1.7 to 1.12
I started to install OST 1.12 over the 1.7 database but the update finished with an unknown error. (Of course, I copied the ost-config.php form 1.7 to 1.12 folder first)
After different try I decided to install 1.12 over a new database, so I created a database and started the update wizard and indicated the new database during the wizard questions. It worked....
My surprise is that I had all my data from 1.7 !!!!! The reason is that I forgot to remove the ost-config.php config file and the wizard did not overwrite it.
This was cool, but I verified that my old database/table structure was identical to the new one. I found only one table that need a new field. (do not ask I forgot which one, I think a group) and two other fields that were not needed anymore.
Ok it is not real tutorial, it just a trick for those who are stuck.