Write all tmux scrollback to a file

gistfile1.md

1. Use prefix + :, then type in capture-pane -S -3000 + Return. (Replace -3000 with however many lines you'd like to save, or with - for all lines.) This copies those lines into a buffer.
2. Then, to save the buffer to a file, just use prefix + : again, and type in save-buffer /home/{user}/filename.txt + return.

(By default Prefix is Ctrl+B.)