cheatsheet for GNU
Suppose user1st and user2nd are the login names of the would-be collaborators on a single computer where the screen session
Commands for user1st who starts the screen session
screen <hit a key to dismiss intro screen> <ctrl-a> :multiuser on <ctrl-a> :addacl user2nd
Note the space between ctrl-a keystroke and : is not meant to be typed; just here for readability (makes the : less likely to be overlooked)
Command for user2nd to join the same screen session
screen -rx user1st/
Start scrollback mode
Note if you are already in scrollback mode when you do this sequence, you will receive the cryptic status message "Must be on a window layer" but it doesn’t hurt anything (you will still be in scrollback mode as intended).
Can use arrow keys, page-up/page-down keys, vi-style navigation, and/or emacs-style navigation. This includes navigation by searching for literal strings, with both vi-style / (forwards) ? (backwards) and emacs-style <ctrl-s key-mappings supported.
End scrollback mode
You will see status message "Copy mode aborted"
Start logging to a file /tmp/scroll-session.txt
<ctrl-a> :logfile /tmp/scroll-session.txt <ctrl-a> :log on
You will see status "Creating logfile /tmp/scroll-session.txt" if the file doesn’t exist; status "Appending to logfile /tmp/scroll-session.txt" if it already does exist.
<ctrl-a> :log off
The resulting status message "Logfile /tmp/scroll-session.txt closed" will remind you where your logfile is located.