I use byobu on sh and was doing some program which was left over for at least 24 hours, I had disconnected from the machine and logged in back after 24 hours is there a way I could see the messages which were on screen in this case.I am using Ubuntu 11.10
Just run
again and it will re-attach to the current session in the background (for the current user). If there is no, it will create a new session.
In case a lot of output has been produced and you'd like to scroll up, use the Copy mode by pressing F7. It will "disconnect" the cursor and allows you to scroll up and search. Use the arrow keys (↑ ↓ → ←) or PageUp / PageDown keys to move around, and Esc to get control back on the shell.
See also: Can Mouse Wheel Scrolling be enabled in Byobu?