See it in job adverts more and more in IT these days. Partly I reckon that it's put in there to scare folk off. Anytime I've installed Linux It's been fairly easy to use. I put it akin to using MacOS to be honest.
So what's the big deal? ( I actually prefer Linux to Windows these days)
What should an IT professional be learning to do on Linux? I can do my job on Windows clients and servers mostly without needing to use PowerShell so what is so special about the Linux OS that folk say you need experience in?
Installed Ubuntu 12 on my secondary laptop last night after install of SSD, and it was pretty straight forward. I browsed around the OS and the GUI is pretty straightforward Linux tbh. I reckon it's saving grace is command line based?
Cheers