Yesterday, I had my external USB hard drive (NTFS) connected to a client's laptop running Ubuntu 18 because I wanted to get some data off of it.
When I was done, I would normally type umount /media/dtweed/Seagate-4TB at the command prompt and then unplug the drive once the command prompt came back. But in this case, I had already closed all of my terminal windows, so I right-clicked on the drive icon on the desktop and selected "Safely remove hardware", and when the icon disappeared, I unplugged the USB cable. This has always worked fine on my own systems (up through Ubuntu 16), but apparently not here. I immediately got a pop-up saying "unable to stop /dev/sdd", and now the filesystem is corrupted.
Needless to say, I'm rather upset about this. It's almost a terabyte of data — not irreplaceable, but it's going to cost me several days to collect it all together in one place again if I can't repair the filesystem.
So, what is the correct way to initiate disconnecting an external drive and be sure that the system is finished updating it?