If you are going to be doing sysadmin work, and you want to get a feel for the attacker mentality, there are a few things you could do. If you have the money,

If you are going to be doing sysadmin work, and you want to get a feel for the attacker mentality, there are a few things you could do. If you have the money, know at least 1 scripting language, and have an aptitude for technology, the OCSP certification course is pretty good. If you want to go the cheaper route, there are lots of books. One introductory text a lot of people like is Hacking: the Art of Exploitation. If you want to learn about web security, the Web Application Hacker's Handbook is a great book. For something less intensive, The Tangled Web would suffice. If you want to learn to harden Linux servers, reedit.com/r/linuxadmin, /r/linux and /r/linux4noobs are great resources. Before you post questions, however, I suggest using the search function because lots of people ask for hardening guides.