Just have installed tmux 2.1 on Ubuntu Server and faced the same problem. The solution for me is to delete all those unknown options and add those lines instead:
set -g mouse-utf8 on
set -g mouse on
Now in tmux 2.1 I can choose a pane, a window and resize everything with a mouse as it was in tmux 1.8
MOUSE SUPPORT section of ‘man tmux’:
“The default key bindings allow the mouse to be used to select and resize panes, to copy text and to change window using the status line. These take effect if the mouse option is turned on.”
UPDATE (since there are a lot of questions):
0 Install:
brew cask install easysimbl
1 Download .dmg file here: https://bitheap.org/mouseterm/
2 Execute:
cd /Volumes/MouseTerm && cp -r MouseTerm.bundle /Library/Application\ Support/SIMBL/Plugins
3 Add this to your .tmux.conf file:
set -g mouse-utf8 on
set -g mouse on
bind -n WheelUpPane select-pane -t= \; copy-mode -e \; send-keys -M
bind -n WheelDownPane select-pane -t= \; send-keys -M
4 Reload tmux
5 Scroll!!!1
I hope this will help. Works for me on iTerm 2/OS X El Capitan/tmux-2.1