Execute the following after the Tmux prefix (ctrl+b by default):

1. Capture scrollback buffer contents: :capture-pane -S -<NUM_LINES_TO_CAPTURE>

2. Write captured contents to file: :save-buffer <OUTPUT_FILE_PATH>

References:

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