I want to know whether there's any good guide on how to setup and manage a linux server (specially ubuntu with Nginx). Any one know what areas I should study in order be a good linux administrator?
if you have a server than learn and practice on itself, the best way is running a good site and doing support stuff yourself which will give you challenges to fix things your own, otherwise the next best option is take some linux courses
Here is a little beginning: Ubuntu Server guide: https://help.ubuntu.com/10.04/serverguide/C/index.html Building a Linux Server, Start to Finish, using Webmin (& Debian) http://woodel.com/ How to build the ultimate Ubuntu/Lighttpd/PHP/MySQL server, and keep it running: http://nanotux.com/blog/the-ultimate-server/ Security: Securing Debian manual (Debian is very much like Ubuntu) http://www.debian.org/doc/manuals/securing-debian-howto/ bodhi.zazen's tutorials: http://bodhizazen.net/Tutorials/ Also if I were you, I'd head over to the ubuntuforums.org for specific help with Ubuntu.
Yeah if you referring to ubuntu, there are plenty of official guides. You can head down to howtoforge as well as their guides are proven tested and working by many followers. They teach you how to setup many standard stuff like hosting with panels, vpns , etc.