A file descriptor is a small integer representing a kernel-managed object that a process may read from or write to. A process may obtain a file descriptor by opening a file, directory, or device,or by creating a pipe, or by duplicating an existing descriptor. For simplicity we’ll often refer to the object a file descriptor refers to as a “file”; the file descriptor interface abstracts away the differences between files, pipes, and devices, making them all look like streams of bytes. We’ll refer to input and output as I/O.