scroll mode

tmux has a scroll mode where you can use page up/page down and arrows to scroll the buffer back. To enter scroll mode, C-b <page up>. To get out of scroll mode, <Esc>. Also C-b [ turns on scroll mode.

sharing

Poor man's screen sharing:

$ tmux -S /tmp/tmux-shared new-session -s session-name
(detach)
$ chmod 777 /tmp/tmux-shared
(attach)

Person 2 attaches:

$ tmux -S /tmp/tmux-shared attach-session -s session-name