fork() can fail
When I was young and really didn't understand Unix, my friend and were summer students at NBS (now NIST), and one fine afternoon we wondered what would happen if you ran fork() forever.<p>We didn't know, so we wrote the program and ran it.<p>This was on a PDP-11/45 running v6 or v7 Unix. The <i>printing</i> console (some DECWriter 133 something or other) started burping and spewing stuff about fork failing and other bad things, and a minute or two later one of the folks who had 'root' ran into the machine room with a panic-stricken look because the system had mostly just locked up.<p>"What were you DOING?" he asked / yelled.<p>"Uh, recursive forks, to see what would happen."<p>He grumbled. Only a late 70s hacker with a Unix-class beard can grumble like that, the classic Unix paternal geek attitude of "I'm happy you're using this and learning, but I wish you were smarter about things."<p>I think we had to hard-reset the system, and it came back with an inconsistent file system which he had to repair by hand with ncheck and icheck, because this was before the days of fsck and that's what real programmers did with slightly corrupted Unix file systems back then. Uphill both ways, in the snow, on a breakfast of gravel and no documentation.<p>Total downtime, maybe half an hour. We were told nicely not to do that again. I think I was handed one of the illicit copies of Lions Notes a few days later. "Read that," and that's how my introduction to the guts of operating systems began.