To scroll within history of the output You would use
You can then use M+V to page up and ^V to page down. I don't know if You can use the real PgUp and PgDown though. My terminal does not send these keys to the tmux. Instead it scrolls itself and not the tmux history.
To exit the copy mode, press ESC
To use your mouse in this mode (called copy mode) press
and enter following:
setw -g mouse on
Note: In tmux < 2.1, the option was named
mode-mouse, and not
Now when You change to the copy mode you can use your mouse to scroll through it.
You can put this command in your ~/.tmux.conf if You want so it loads every time You run tmux.
Update: As of tmux 1.5 this option makes using the scroll wheel automatically switch to copy mode and scroll back the tmux scrollback buffer. It is not necessary to first hit
[ any more. Scrolling back down to the prompt also ends copy mode automatically.