I'm confused by the way you phrase your question.
With the shared hosting, a customer account shares the available resources of a cluster of machines with other customers. Each plan that a customer signs up for determines how much of these resources the customer can use - such as users, disk space, and virtual hosts. No single customer is in charge of a particular machine.
As for as the operating system goes, a shell user gets access to a command line interface by telnet/SSH. But as above, a shell user will be one of many users and you don't get "root".
However the shell user can do a lot of things such as compile your own version of PHP, use cron, run non-CGI scripts and programs, etc.
Perl / MySQL / HTML+CSS