So, you decided you need GitLab (well, the only good open source Git on premise) and want to install it. You could do so by following this and later HUGE installation guide. BUT then you would definitely come across different problems such as described here. Good luck with troubleshooting them. I doubt you will be successful, because even I wasn’t.
So what’s the solution? Well DO follow this guide and you will be installing GitLab from packager.io. Not only it is very easy and straightforward to install it. But you can also configure it very easily, much more than from “normal” installation guide.