The TTY demystified
The TTY subsystem is central to the design of Linux, and UNIX in general. Unfortunately, its importance is often overlooked, and it is difficult to find good introductory articles about it. I believe that a basic understanding of TTYs in Linux is essential for the developer and the advanced user. Beware, though: What you are about to see is not particularly elegant. In fact, the TTY subsystem — while quite functional from a user's point of view — is a twisty little mess of special cases. To understand how this came to be, we have to go back in time. In 1869, the stock ticker was invented. It was an electro-mechanical machine consisting of a typewriter, a long pair of wires and a ticker tape printer, and its purpose was to distribute stock prices over long distances in realtime. This concept gradually evolved into the faster, ASCII-based teletype. Teletypes were once connected across the world in a large network, called Telex, which was used for transferring commercial telegrams, but th