What's a file descriptor's “exception”?

Question

When one calls select() asking which file descriptors have \"exceptions\" waiting, what does that mean?

How does one trigger one of these \"exceptions\"?

If anyo

Answer 1

Indeed there seems to be very little information on this. Thankfully there's an existing question with a very good answer.

In the case of Linux, for example, it can denote out-of-band data being received on a stream socket, or "a state change occuring on a pseudoterminal slave connected to a master that is in packet mode" (TLPI 63.2.1).