How do I copy files from old iMac (2009) to usb using single user mode if I can't remember the exact names of the files?
First open a terminal. There you can do all things you would do with Finder.

The Terminal offers a range of commands you can use:


To see, what is in the current directory, run ls.
To copy a file, use cp &lt;from&gt; &lt;to&gt; (and replace  and  with the correct filenames or paths)
To see where disks are mounted, you can use df, mount or ls /Volumes
To change folders use cd &lt;foldername&gt;


You don't need to fully type out all filenames. You can use autocomplete using the Tab key.