Postmaster start up problems (can't create lock file )

I'm trying to start my postgres server and it gives me the following errror

FATAL:  could not create lock file "/var/run/postgresql/.s.PGSQL.5432.lock": Permission denied

Now obviously to touch the file that the error message is talking about, one needs root permission that the user account under which my postmaster is runnnig doesn't have.

Can anyone tell me the fix.

Thanks