I'm looking for a Linux distro (or some Unix flavor...) that is similar to HP-UX so that I practice the command line as well as other things. This is in order to get CSA Certification. Which distro should I use? I already know Linux basics.
I'm afraid no Linux distribution resemble HP-UX (or AIX, Solaris for that matter) enough to be helpful in your case.
While all Unix and Unix like OSes share a similar posix layer, there is a major difference on the system administration side which is what CSA certification is about I presume.