pty

PTY is an acronym that commonly refers to a pseudo-terminal in Unix-like operating systems. A pseudo-terminal is a pair of devices—a master and a slave—that together emulate the behavior of a physical terminal. The master side is controlled by a program, while the slave side is presented to another process as if it were a real terminal.

How it works: a program that needs terminal interaction allocates a PTY pair. On Linux and Unix, this is typically done by requesting a master device (for example via posix_openpt) and then granting access and unlocking the corresponding slave with grantpt and unlockpt, followed by obtaining the slave’s path with ptsname. The master device is used by the controlling program to send input and read output, while the slave device behaves like a traditional terminal for the process that runs on it (for example a shell or text editor). Terminal semantics such as echoing, line discipline, and character buffering are provided by the system for the slave side.

Typical uses include terminal emulators (such as xterm, GNOME Terminal), remote login services (SSH), and terminal multiplexers (screen, tmux) that require programmatic control of a terminal session. PTYs allow automated tools to interact with interactive programs by simulating a user at a terminal, while keeping the controlling process separate from the program that runs inside the terminal.

In relation to traditional TTYs, a PTY pair creates a virtual TTY where the slave side exposes a real terminal interface to a process, and the master side provides the control channel to another program. Other meanings of the acronym PTY exist in different domains, but in computing this article refers to pseudo-terminals.