My current config for tmux is to use ` for prefix key
set-option -g prefix `
How can I change this to use the
ALT key. Nothing else in combination.
The ALT key doesn't send a specific key code to the terminal; rather, it modifies the key code sent by another key when it is held down simultaneously. As such, the ALT key by itself cannot be used as the tmux prefix.
[Edit: As Keith points out, the following will technically work but will almost certainly not behave the way you like.]
One workaround might be to configure your local setup or terminal emulator to change the behavior of the ALT key, perhaps to act as the Escape key. Then the following could work: