I agree with the previous posting that two weeks is certainly not enough if you ask now where to start! If the exam can not be done later, or if you really need it for your job, then you should get yourself a spare PC and install RHEL or CentOS on it. Then start using it for quite everything ranging from bash scripting to web serving, logging in via SSH, running and accessing ftp, setting up a bind server, making backups etc, plus and all kind of weird things that effectively can break the system - you have to do this the whole day for the next two weeks if you want to come to speed on these issues. Be prepared for a lot of re-installs. This will be a crash course!