I must second Arnold's statement. Quite frankly you are wasting your time learning how to install WeBWorK 2.17 (or any version before that). WeBWorK 2.17 relies on modperl2 which is practically obsolete. So eventually, you will need to upgrade and then you will have to learn how to work with 2.18 and beyond, and as Arnold stated, from the administrative standpoint it is completely different since it uses the modern Perl library Mojolicious instead of modperl2. In addition, there are many new features and improvements to WeBWorK 2.18 (and more in 2.19) that you (and your users) will be missing out on. Eventually (actually already for some problems), you will also run into problems with PG 2.17, because the OPL is being updated to work with new things in PG that were not in previous versions of PG.