While performing an upgrade through UMC or on command line the upgrade process just stalls and you do not see any progress. Not even after waiting a couple of hours or a day.
While the progress is stalled you see a process called “cdrom” in the process list:
ps ax | grep cdrom 23277 ? R+ 0:00 cdrom 24415 pts/0 R+ 0:00 grep cdrom
This indicates the updater tries to access a cdrom which is not inserted and waits for a key to be pressed when the cdrom is inserted. In this case the cdrom entry was added manually earlier.
Remove all previously added lines in your file
echo > /etc/apt/sources.list apt update
Restart the upgrade process then.