Knowing something in theory and experiencing something for real are two different things. I know of course that Android is based on a Linux kernel and shares many things with desktop Linux distributions. But it's all nicely hidden under the Android user interface so the concept felt quite abstract to me, even after using 'adb' for a long time and having experience with Debian running on ARM driven Raspberry Pis and all. But when I recently opened a terminal on the device itself and used the shell like I would use one on a PC with a hardware keyboard, auto command completion and on top of that write shell scripts with my favorite shell based text editor 'nano', e.g. to issue the commands to enable write access of the system partition and start the editor to modify the 'hosts' file, it started to feel quite different. Yes, there's really something under the hood I'm quite familiar with and it 'feels' very good indeed.