Thanks for the replies and the luck which I need the most
, it really helped a lot.
I will try the Institte provided books for basic ubderstanding, as going deeper without basic knowledge will lead me nowhere, so I will try the labs at the end of each unit and some other labs.
But still I would want to know which are the main topics I can focus on, like Apache, NFS, Squid, DHCP, DNS, etc. Your views are of great help to me.