Tmux scrolling

To begin scrolling you need to press Ctrl-b + [ ,assuming Ctrl-b is set as the prefix, and then use the arrow keys (or hjkl if you use vi mode) to move around.

To scroll a little bit faster you can use the following, adding the key bidings for vi mode as that is what I use.

Function Key Combination
Half page down C-d
Half page up C-u
Next page C-f
Previous page C-b

Source