Question

When reading about pipes in Advanced Programming in the UNIX Environment, I noticed that after a fork the parent can close() the read end of a pipe and it doesn’t close the read end for the child. When a process forks, does its file descriptors get retained?

What I mean by this is that before the fork the pipe read file descriptor had a retain count of 1, and after the fork 2. When the parent closed its read side the fd went to 1 and is kept open for the child. Is this essentially what is happening? Does this behavior also occur for regular file descriptors?

Answer 1

As one can read on the man page about fork():

The child process shall have its own copy of the parent’s file
descriptors. Each of the child’s file
descriptors shall refer to the same
open file description with the
corresponding file descriptor of the
parent.

So yes, the child have exact copy of parent’s file descriptors and that refers to all of them, including open files.