You really should use mysqli_* or else one day in the future when you upgrade PHP, your code will just stop working, and you'll have PHP complaining that mysql_connect() doesn't exist. When functions are deprecated, it is a sign that you must begin migrating to the alternatives. I highly recommend using mysqli_* as the syntax is pretty much the same as mysql_*.
If you still insist to use mysql_*, then you can tell PHP not to report the use of deprecated functions. Look through /etc/php/php.ini and search for error_reporting. Append & ~E_DEPRECATED to it. For example, my PHP config has: