How to select rectangles in TMUX

Just add to your .tmux.conf file:

set-window-option -g mode-keys vi
bind-key -T copy-mode-vi 'v' send -X begin-selection
bind-key -T copy-mode-vi 'y' send -X copy-selection-and-cancel
bind-key -T copy-mode-vi 'r' send -X rectangle-toggle