I recently completed the first week of Red Hat Systems Admin training. Mostly basic stuff and items I was fairly familiar with, with two notable exceptions: Logical Volume Management and SELinux.  I only had a rudimentary understanding of their use and usefulness and I anticipated that I would not see the need for either one or both of them. I am now convinced they are very useful and not as difficult to manage as I thought. I have already put some of the skills I learned to very good use on one of our departmental file servers — and saving a great deal of time — rather than doing what was needed without using them.  What would have taken possibly hours was accomplished in 15 minutes or so.