There must be some general principals though? The same thing could be said of programming however you are going be a useless Java programmer if you don't understand encapsulation. Also if you applied for a Java job you are expected to know the core set of Java functions.
... or the other 3 for that matter...
There are general principles, sure, but when it goes to systems administration, at its most basic, it is doing specific single tasks, being running a command, editing an option in a conf file, etc, and knowing the general principles of any aspect of the OS may not really help you in being able to successfully carry out a task. And it's been my experience that tech interviewers ask questions about specific tasks. About the only questions I've ever had posed to me related to principles, is shell theory, which to some is like arguing politics or religion.