Windows and Linux from a DBA prospective

I’m considering moving into the DBA field and have begun reading in areas of SQL and Database design theory however I’m not sure how to approach Windows and Linux.

I’ve passed the CompTIA A+ in 2006 so I’m familiar with Windows for a 1st line support perspective however should I be reading literature which is more catered toward DBA and if so can anyone suggests an appropriate book?

I will also need a suggestion for Linux.

Many thanks