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Why is it important for a process to close any pipe file descriptors it does not intend to use?
if your pipe spans threads (within the same process), then do not close the unwanted ends of the pipe. This is because the file descriptor is held by the process, and closing it for one thread will close it for all threads, and therefore the pipe will become unusable.
Why must a daemon process close all standard file descriptors?
Unneeded file descriptors should be closed. This prevents the daemon from holding open any descriptors that is may have inherited from its parent (which could be a shell or some other process).
Which is the correct way to close a file descriptor?
In that aspect, close is a bit like free: it is invalidating the value (file descriptor for close, pointer for free) passed to it. When possible, you could set the file descriptor to -1 (or some other invalid value) after a successful close (2), so code close (fd); fd = -1; for example.
What happens to file descriptors when the process is killed?
Yes, the file will be automatically closed when the process terminates, regardless of the reason for the process termination. This is documented in POSIX. In “ Consequences of Process Termination ”, among other consequences:
What happens if FD is the last file descriptor?
If fd is the last file descriptor referring to the underlying open file description (see open (2)), the resources associated with the open file description are freed; if the file descriptor was the last reference to a file which has been removed using unlink (2), the file is deleted. close () returns zero on success.
What happens when no process has an open read descriptor?
When a process tries to write to a pipe for which no process has an open read descriptor, the kernel sends the SIGPIPE signal to the writing process. By default, this signal kills a process. write (), on error, -1 is returned, and errno is set appropriately.