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For those looking for a simple answer, just use prefix + :, then type in capture-pane -S -3000 + return (Replace 3000 with however many lines you'd like to save.) This copies those lines into a buffer.

Then, to save the buffer to a file, just use prefix + : again, and type in save-buffer filename.txt + return, replacing filename with whatever you'd like.

(By default prefix is ctrl + b.)

With tmux 1.5, the capture-pane command accepts -S and -E to specify the start and end lines of the capture; negative values can be used to specify lines from the history. Once you have the data in a buffer, you can save it with save-buffer.

Here is an example binding (suitable for .tmux.conf) that wraps it all up with a prompt for the filename:

bind-key P command-prompt -p 'save history to filename:' -I '~/tmux.history' 'capture-pane -S -32768 ; save-buffer %1 ; delete-buffer'

This captures (up to) 32768 lines of history plus the currently displayed lines. Starting with tmux 1.6, you can use numbers down to INT_MIN if your pane has a history that is deeper than 32Ki lines (usually up to 2Gi lines). Starting in tmux 2.0, you can use capture-pane -S - to mean “start at the beginning of history” (i.e. no large, hard-coded negative number).

Note: The number of lines in the saved file will not always be equal to the pane’s history limit plus its height.

When a pane’s history buffer is full, tmux discards the oldest 10% of the lines instead of discarding just one line. This means a pane’s effective history depth will sometimes be as low as 90% of its configured limit.

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.

Here's a tmux plugin that enables this:

https://github.com/tmux-plugins/tmux-logging

After you install it, save the entire scrollback with prefix + alt-shift-p.

If you want something you can run from the command line (instead of using your tmux prefix keys), try running:

tmux capture-pane -pS -1000000

If you run it and it seems to not do anything, that's because it's outputting exactly what was just on your screen, so it looks the same.

Of course, you can also pipe it into a file:

tmux capture-pane -pS -1000000 > file.out

See the tmux man page and search for capture-pane for more things you can do (like capture escape sequences in case you want to preserve color, or specify whether you want multiple visual lines to be joined when they don't contain a new line)

This is actually very easy.
Enter the command mode by press prefix key then :.
Then do capture-pane -S -<line number you want to dump>
Then save-buffer <filepath>

That file contains all the scrollback output. You should delete the buffer afterwards for safety reason.

How can I write all the scrollback in a tmux session to a file?

I use this in my ~/.tmux.conf, and now when I exit my running shell, pane output is saved to unique log file:

set -g remain-on-exit
set-hook pane-died 'capture-pane -S - -E - ; save-buffer "$HOME/logs/tmux/tmux-saved.#host_short-#session_id:#window_id:#pane_id-#pane_pid-#client_activity.log"; delete-buffer; kill-pane'