What is ttys?

Understanding ttys

A tty (short for "teletypewriter") is a terminal interface, traditionally a physical device, that allows users to interact with a Unix-like operating system. Today, it primarily refers to virtual terminal devices. ttys serve as a bridge between the user and the kernel, enabling input (commands) and output (text) to be exchanged.

Key aspects of ttys:

• Types of ttys:

  • Physical Consoles: The directly attached keyboard and screen (e.g., /dev/console).
  • Virtual Terminals: Multiple logical terminals accessed via keyboard shortcuts (e.g., Ctrl+Alt+F1 through F7).
  • Pseudo-terminals (PTYs): Created by programs like xterm, gnome-terminal, or SSH to provide a terminal interface within a graphical environment or over a network. These are usually in /dev/pts/*.
  • Serial Ports: Older devices connecting via serial communication protocols.

• Naming Convention: Ttys are typically represented as files in the /dev directory. For example, /dev/tty1, /dev/tty2, /dev/pts/0, etc.

• Purpose:

  • Provide a text-based interface for user interaction.
  • Allow users to execute commands and run programs.
  • Display output from programs.

• Controlling Terminal: Each process connected to a tty has a controlling terminal. Signals (like Ctrl+C) are sent to all processes in the foreground process group of the controlling terminal.

• Utilities: Common commands for working with ttys:

  • tty: Prints the name of the current tty.
  • who: Shows who is logged in and on which ttys.
  • ps: Can be used to determine which processes are associated with a specific tty.

• Importance: Ttys are fundamental to the operation of Unix-like systems, providing a crucial link between the user and the operating system kernel. They are essential for command-line interaction, scripting, and remote access.