Good question. Depends on the OS. In the case of Linux (and other Unixish OSes), getty is the program that makes a terminal or console session work on the host

Good question. Depends on the OS. In the case of Linux (and other Unixish OSes), getty is the program that makes a terminal or console session work on the host side. Getty usually launches a program, login, that takes your username and password, retrieves your account's settings and launches your interactive shell (something like bash, zsh, fish or oil) when you successfully authenticate. Incidentally, tools like screen and byobu allow multiple terminals to attach to the same shell by multiplexing the terminal (not the shell).