Why does tmux set TERM=screen?

Question

How does tmux set the terminal to use (as reflected in the TERM environment variable).

For example. If I log in via ssh bash reports:

>set | grep TERM
TERM=xterm-256-color

If I then run tmux and from within tmux and do the same:

>set | grep TERM
TERM=screen

I think this is not always the case though since noticing it I have not managed to make tmux say anything else.

This relates to fake/mock/background terminal for testing an ncurses application

Where I am I trying to understand how the terminal emulation affects the resulting behaviour of an ncurses app.

Answer 1

That's controlled by the default-terminal server option in .tmux.conf:

set -g default-terminal "screen-256color"

From the docs:

default-terminal terminal Set the default terminal for new windows created in this session - the default value of the TERM environment variable. For tmux to work correctly, this must be set to ‘screen’, ‘tmux’ or a derivative of them.

It is considered good practice to not touch the TERM variable directly (do not set it manually in .bashrc or .zshrc but instead rely on tmux to generate it from .tmux.conf).