I was using OJS since 2010, Currently i wan to migrate all hosted services to New Ubuntu Server, 16.04
how ever I couldn’t use OJS on this server, may be PHP 7 compatibility problem.
Have you tried updating via sudo apt-get update in a shell? You can also use which php to see where your PHP is and then compare with your installation to see if the pointers are correct.
What version of OJS3 you are using?
OJS 3.0.2 works perfectly on Ubuntu16.04 with latest PHP. I recently updated the system and all soft for latest versions on our production site.
You need to check your PHP logs for errors. Look for fatal errors.