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Can I upgrade it to latest one, without disturbing my OS?
Sure, that’s up to you.
If OS or PHP or My SQL need to upgrade, how to upgrade?
In order to run v1.16.1 you must upgrade your PHP to 8.0 and it’d be best to upgrade MySQL to 8 as well. If you do not know how to upgrade them please refer to your server’s documentation.
If I will install a fresh RHEL 8.2 will all PHP and MY SQL to latest one, am i able to restore the SQL from old OSTicket?
Yes, you can install all the requirements on a new server, mysqldump your current database, move the sql dump file to the new server, copy your include/ost-config.php
file to the new server, import your data dump to MySQL on the new server, put the new osticket code in place, place the config file in the include
directory, and update the database information in the config file to match your new server.
Cheers.