GNU Screen is the original terminal multiplexer and still ships by default on countless servers. Its core promise is simple but powerful: start a session, detach from it, and your processes keep running even if your connection drops. Reattach hours later and everything is exactly as you left it.

It remains popular precisely because it's everywhere—if you SSH into an unfamiliar machine, Screen is often already installed when tmux isn't. Key features include detachable persistent sessions, window splitting, and a built-in serial-port terminal mode that's genuinely useful for talking to routers and embedded devices. Configuration lives in ~/.screenrc.

bash
screen -S deploy      # start a named session
# Ctrl-a c            create a new window
# Ctrl-a d            detach
screen -r deploy      # reattach later

While tmux has overtaken it in modern setups, Screen's ubiquity and rock-solid stability keep it firmly in the sysadmin toolbox.