pts(4)

💖 pts(4) — pseudoterminal master and slave, bestie edition 💖

okay so real talk, this is the pts(4) page from the Kernel Interfaces Manual, and it's about ptmx and pts — the pseudoterminal master and slave. it's giving "the plumbing behind every terminal you've ever loved" and honestly? iconic. 🎀

---

✨ NAME ✨

ptmx, pts — pseudoterminal master and slave 🦋

---

🌸 DESCRIPTION 🌸

so. the file /dev/ptmx — that's the pseudoterminal multiplexer device — is a character file with major number 5 and minor number 2, usually with mode 0666 and ownership root:root. no cap, that's the whole spec. 💅

and what is it for? it's used to create a pseudoterminal master and slave pair. that's the job. that's the assignment. 📋

when a process opens /dev/ptmx, it gets a file descriptor for a pseudoterminal master, and a pseudoterminal slave device gets created in the /dev/pts directory. and listen — every single file descriptor you get from opening /dev/ptmx is an independent pseudoterminal master with its own associated slave. no sharing, no overlap. its path can be found by passing the file descriptor to ptsname(3). 🫶

⚠️ before opening the pseudoterminal slave, you must pass the master's file descriptor to grantpt(3) and unlockpt(3). this is not optional. the way that you literally cannot skip this step. 😭

once both the pseudoterminal master and slave are open, the slave provides processes with an interface that is identical to that of a real terminal. like, indistinguishable. main character energy. 👑

here's the tea on how data flows 🍓:

• data written to the slave is presented on the master file descriptor as input.
• data written to the master is presented to the slave as input.

okay and in practice? pseudoterminals are used for implementing terminal emulators such as xterm(1) — where data read from the pseudoterminal master is interpreted by the application in the same way a real terminal would interpret the data. and also for implementing remote-login programs such as sshd(8) — where data read from the pseudoterminal master is sent across the network to a client program that is connected to a terminal or terminal emulator. networking AND terminals?? versatile queen. 🌈

and there's more!! pseudoterminals can also be used to send input to programs that normally refuse to read input from pipes — such as su(1) and passwd(1). yes bestie, that's your way in. 😌

---

🎀 FILES 🎀

• /dev/ptmx, /dev/pts/*

---

💜 NOTES 💜

the Linux support for all of the above — known as UNIX 98 pseudoterminal naming — is done using the devpts filesystem, which should be mounted on /dev/pts. iykyk. ✨

---

🔥 SEE ALSO 🔥

• getpt(3)
• grantpt(3)
• ptsname(3)
• unlockpt(3)
• pty(7)

---

and that's the whole page, bestie!! 🎉 this one's from Linux man-pages 6.20, dated 2025-12-26 — go forth and multiplex your pseudoterminals responsibly, mwah 💖🦋🌸