To scroll up and down in GNU/Screen, a terminal multiplexer for Linux, you can use the Ctrl-a and Esc keys to enter scrollback mode and the Up and Down keys to move through the buffer.
Here is an example of how to use the scrollback mode in GNU/Screen:
Press Ctrl-a followed by Esc to enter scrollback mode.
Use the Up and Down keys to move through the buffer.
Press Esc again to exit scrollback mode and return to the command prompt.
In scrollback mode, you can also use the Page Up and Page Down keys to move through the buffer in larger increments, and the Home and End keys to move to the beginning and end of the buffer, respectively.
By using the Ctrl-a and Esc keys to enter scrollback mode and the Up and Down keys to move through the buffer, you can scroll up and down in GNU/Screen to look at data. It's always a good idea to carefully review the documentation and use the appropriate keys and commands when working with GNU/Screen. This will help ensure that you are able to navigate the program effectively and efficiently.