Write all tmux scrollback to a file

https://unix.stackexchange.com/questions/26548/write-all-tmux-scrollback-to-a-file

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.)