I'm thinking of it as a test for the simplest possible thing I can ask someone that will tell me immediately if they're worth talking to or not. I mentioned this in another post, the one I use that people bomb most often is: "I want to run this command on 100 files. Write me a for-loop in the shell of your choice to do it."
That's kind of terrifying that someone can't do that can say they are an SA. Did anyone you interviewed mention xargs as a BTW solution after presenting the for-do loop? I'm currently trying to figure out if one of the SA's at a current client actually does not know how to use tar, gzip, and scp, so I know where you are coming from, but still.
When you previously said "complicated applications in (python|perl|ruby)", did you mean someone who knew both front- and back-end? That implies someone who also knows Javascript, CSS, HTML, and a few databases, not to speak of one or more web frameworks, proxies, load balancers, etc.
When you say "debug and port C/C++ programs", did you mean someone who knows enough about Windows to port a program written there to run on Linux? Or someone who knows enough about BSD to port to Linux? Or someone who knows enough about [AIX|HP-UX|Solaris] to port to Linux? Port what, pure userland programs or stuff that messes around with ioctl calls? Debug from a hand-built in-memory circular log, core with no symbol table, using Dtrace, or just some judicious printfs or logging?
Depending upon how you specify what you want, you don't have to go far these days to stray a long distance from a "Linux SA" role, where even a "Senior Linux SA" job title won't cut it; you are moving closer to a Free Electron, and those people don't come cheap.