the TTY driver is the most obscure part of the system

You almost never need to think about it, but when I’ve wanted to do something weird (like put a terminal in a web browser) understanding the driver is SO USEFUL

when you start your terminal emulator, it asks the OS to create a “pseudoterminal pair” which is a pair of two files

terminal emulator <-> TTY <-> TTY driver <-> TTY <-> program

a “TTY” is the program’s side of the pair

programs use it to:

• communicate with the terminal emulator by reading/writing bytes
• configure the TTY driver (more on the next page!)

Run tty fo see the current TTY!

the TTY driver is why Ctrl+C does the same thing relatively consistently

program: you press Ctrl+C, I send a signal!
well, unless the program tells me it wants the raw bytes!

some things the TTY driver is in charge of

(you might think “these are unrelated” and you’d be right)

• storing the terminal window’s size
• sending a SIGHUP signal when you close your terminal
• a basic mode for entering text called “canonical mode”
• pausing the output and confusing you when you press Ctrl+S
• tracking which process is in the “foreground” and sending what you type there