I'm a PHP web developer and I'd like to start learning more about system administration and was wondering if anyone had any good resources/starting points to look at. I have an old computer I can install Linux on and play around with if necessary. The server a couple of my apps run on right now use CentOS so I was thinking just learning that but if that is not a good starter I'm open to using other distros.
I'm comfortable with very basic UNIX commands right now (cd, cp, ls, rm, really weak sauce stuff like that). My main motivation to learn about this is I want to play around with tools for web development (like XHProf, buildBot, Selenium, etc) but realized I don't even know how to install anything. I'm very comfortable developing web apps but I feel like I should know at least a little bit about how web servers work. I also would like to eventually be able to monitor server load, performance, etc since I am into performance.