Judging by the thread here, the very premise seems difficult to imagine today. But there was a time, indeed, when end users regularly logged in to a Unix system

Judging by the thread here, the very premise seems difficult to imagine today. But there was a time, indeed, when end users regularly logged in to a Unix system as themselves, and their shell specified the program they could run, like a line of business app or something, and short of exploiting a vulnerability in that app, that was all they could access, sitting there at a physical terminal typing on a keyboard. There just weren’t that many other ways to spawn a process. Meanwhile, these days, it seems like the only user ever running anything is docker, and “access control” has an entirely different set of meanings.