What resources would you recommend for self-education or some courses in the field of "System Administration"?

Question

System administration

I want to advance in this area to gain experience for further self-realization.

Answer 1

a few thoughts
1. about the courses - the theoretical base is certainly important, but without practice all this will be forgotten
2. it would be nice to get a job as an assistant administrator. a lot of money is unlikely to be given, but those. the base will be larger than at home + real experience from crimping the cable to solving user issues
I give a number of links, maybe this will help you decide
Linux or Windows
system administration unix
installation
gentoo specifically on linux or freebsd
If you want Windows, but immediately install a terminal server + active directory, GPO policies, accesses
I tried to write a coherent, but very general question

Answer 2

In the piggy bank:
Kenin A.M. - Practical Guide for System Administrator - 2010
Kenin A.M. - Self-instruction manual for a system administrator - 2012
Olifer V.G., Olifer N.A. - Fundamentals of Computer Networks - 2009
Nemeth E., Snyder G., Hein T., Waley B. - Unix and Linux. System Administration Guide - 2012
Evi Nemeth - Unix and Linux. System Administrator's Guide - 2012
Filimonov - Building Multiservice Ethernet Networks - 2007
and Journal System Administrator