How do I scroll in tmux?

Ctrl-b then [ then you can use your normal navigation keys to scroll around (eg. Up Arrow or PgDn). Press q to quit scroll mode.

Alternatively you can press Ctrl-b PgUp to go directly into copy mode and scroll one page up (which is what it sounds like you will want most of the time)

In vi mode (see below), you can also scroll the page up/down line by line using Shift-k and Shift-j (if you're already in scroll mode). Unshifted, the cursor moves instead of the page.

Excerpts from the man page:

tmux may be controlled from an attached client by using a key combination of a prefix key, ‘C-b’ (Ctrl-b) by default, followed by a command key.

 The default command key bindings are:

[           Enter copy mode to copy text or view the history.

Function                     vi              emacs
--------                     --              -----
Half page down               C-d             M-Down
Half page up                 C-u             M-Up
Next page                    C-f             Page down
Previous page                C-b             Page up
Scroll down                  C-Down or C-e   C-Down
Scroll up                    C-Up or C-y     C-Up
Search again                 n               n
Search again in reverse      N               N
Search backward              ?               C-r
Search forward               /               C-s

Plus a bunch more. Note that you have to press C-b twice if you use that for page up since C-b is bound as the command key. See the man page for information on prefacing a copy mode command with a repeat count.

You can set the key binding mode using Ctrl-b, then

:set-window-option mode-keys emacs

or vi.

Well, you should consider the proper way to set scrolling: add in your ~/.tmux.conf

set -g mouse on        #For tmux version 2.1 and up

or

set -g mode-mouse on   #For tmux versions < 2.1

It worked for me in windows and panes. Now tmux is just perfect.

Practical tmux has more info on tmux.conf files.

From my .tmux.conf:

# Sane scrolling
set -g terminal-overrides 'xterm*:smcup@:rmcup@'

This enables native xterm scrolling.