Which distribution enables this by default ?

EDIT: Apparently Ubuntu, but not Debian, SuSE, Arch, etc. Well, TIL.

> No, you can't. Try it.

You definitely can, it's just that that as you said, gdb just can't attach to anything but a child process; making gdb only work with a process it spawned itself.

Anyway, in addition to changing .profile, you still can do practically everything including modifying SHM segments, writing to pipes, sockets, etc. You could start closing feature by feature (e.g. remove /proc like Android), but for some reason it doesn't seem like the right approach.