This is a program which locks a terminal. It's like vlock or lock(1)
from the BSDs. It's meant to be used with tmux's lock-command.

Please note that this doesn't prevent attaching a new tmux session.
It doesn't prevent switching to TTY2, logging in, and running kill
-9 tlock. It doesn't prevent <Enter>~<Control+Z> if the tmux session
is accessed over ssh (although ssh -e none should prevent that).