Classic deep-dive into Linux TTY subsystem: history from 1869 teletypes through UARTs, line disciplines, PTYs, and job control signals.
Key Takeaways
The TTY subsystem layers UART driver, line discipline (N_TTY), and TTY driver together; each is a passive object invoked by process or interrupt context.
Line discipline sits between UART and application, providing cooked/raw mode, edit buffer, echo, and linefeed conversion before bytes reach userspace.
Session management and job control (foreground process group, SIGTSTP, SIGHUP) are handled by the TTY driver cooperating with the shell as session leader.
Pseudo terminals (PTYs) move terminal emulation to userland while keeping TTY session management intact; xterm, ssh, and screen all stack PTYs.
The kernel communicates asynchronously with processes via signals, not ioctl, making TTY signal handling notoriously complex.
Hacker News Comment Review
No substantive HN discussion yet; single comment notes the page is a long-standing reference that resurfaces periodically as a recommended deep read.
