I had standard key bindings which appeared to be a bit different than in @jasonwryan's answer and didn't change anything in config.

Below is recipe that worked for me. Maybe you will find it useful if you don't want to make any changes in tmux config and just want to quickly copy some of the scrollback.

Prefix == Ctrl+b in my tmux (tmux 1.6, debian 7).

1. Enter select mode: Prefix + [.
2. Start selection: Space.
3. Highlight necessary text using vim navigation (for instance, use arrow keys or press gg to reach beginning of output history).
4. Actually copy in internal clipboard using Enter. You will be exited from copy mode.
5. Open any file using vim (probably on new tmux tab) and paste content you copied before using Prefix + ].
6. Then you may do cat of that file or use output how you need.

I had standard key bindings which appeared to be a bit different than in @jasonwryan's answer and didn't change anything in config.

Below is recipe that worked for me. Maybe you will find it useful if you don't want to make any changes in tmux config and just want to quickly copy some of the scrollback.

Prefix == Ctrl+b in my tmux (tmux 1.6, debian 7).

1. Enter select mode: Prefix + [.
2. Start selection: Space.
3. Highlight necessary text using vim navigation (for instance, use arrow keys or press gg to reach beginning of output history).
4. Actually copy in internal clipboard using Enter. You will be exited from copy mode.
5. Open any file using vim (probably on new tmux tab) and paste content you copied before using Prefix + ].
6. Then you may do cat of that file or use output how you need.

I had standard key bindings which appeared to be a bit different than in @jasonwryan 's answer and didn't change anything in config.

Below is recipe that worked for me. Maybe you find it useful if you don't want make any changes in tmux config and just want quickly copy some of scrollback.

Prefix == Ctrl+b in my tmux (tmux 1.6, debian 7).

1. Enter select mode: Prefix + [.
2. Start selection: Space.
3. Highlight necessary text using vim navigation (for instance, use arrow keys or press gg to reach beginning of output history).
4. Actually copy in internal clipboard using Enter. You will be exited from copy mode.
5. Open any file using vim (probably on new tmux tab) and paste content you copied before using Prefix + ].
6. Then you may do cat of that file or use output how you need.

I had standard key bindings which appeared to be a bit different than in @jasonwryan's answer and didn't change anything in config.

Below is recipe that worked for me. Maybe you will find it useful if you don't want to make any changes in tmux config and just want to quickly copy some of the scrollback.

Prefix == Ctrl+b in my tmux (tmux 1.6, debian 7).

1. Enter select mode: Prefix + [.
2. Start selection: Space.
3. Highlight necessary text using vim navigation (for instance, use arrow keys or press gg to reach beginning of output history).
4. Actually copy in internal clipboard using Enter. You will be exited from copy mode.
5. Open any file using vim (probably on new tmux tab) and paste content you copied before using Prefix + ].
6. Then you may do cat of that file or use output how you need.