tty(4)

✨ tty(4) — Kernel Interfaces Manual ✨

okay bestie, sit down, because we're talking about tty(4) — the little manpage with main character energy 💅 welcome to the Kernel Interfaces Manual, section 4, where the cool stuff lives.

🎀 NAME 🎀

tty — controlling terminal 🖥️✨

🌸 DESCRIPTION 🌸

So. The file /dev/tty is a character file. Not like a character character, like a device file. It has major number 5 and minor number 0, and its mode is usually 0666 with ownership root:tty. It's literally a synonym for the controlling terminal of a process — if there is one. If there isn't… well. That's a vibe check it might not pass 🙈

On top of all the ioctl(2) requests that the device tty points at already supports, there's one extra request that gets supported here: TIOCNOTTY. she's special, your honor 👑

💫 TIOCNOTTY 💫

Basically: detach the calling process from its controlling terminal. bye bestie 👋

If the process is the session leader, then SIGHUP and SIGCONT signals get sent to the foreground process group, and all processes in the current session lose their controlling tty. not a drill 😭

careful with this one — it ripples out to the whole session when a session leader calls it, fr fr

Okay and super important: this ioctl(2) call works only on file descriptors connected to /dev/tty. Only. Just that one. no substitutes 🚫

So like, who even uses this? Daemon processes, when a user invokes them at a terminal. Here's the move they pull:

1. The process attempts to open /dev/tty 🫶
2. If the open succeeds, it detaches itself from the terminal by using TIOCNOTTY ✂️
3. If the open fails, it is obviously not attached to a terminal and does not need to detach itself. no harm, no foul, no drama 💅

iconic honestly. ate and left no crumbs.

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📁 FILES 📁

• /dev/tty

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👀 SEE ALSO 👀

• chown(1)
• mknod(1)
• ioctl(2)
• ioctl_console(2)
• ioctl_tty(2)
• termios(7)
• ttyS(4)
• vcs(4)
• pty(7)
• agetty(8)
• mingetty(8)

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and that's the whole page, bestie, no cap 💖 this lil slice of the Linux man-pages 6.20 dropped on 2026-07-02, and you now know it through and through. periodt. 🦋✨