Unmounting disks in Ubuntu is a bit more challenging than it should be. Say you have an external drive mounted on /media/disk. Trying the standard
sudo umount /media/disk
will often result in an error such as
umount: /media/drive: device is busy.
It is advisable to check what files may be open on the drive with
lsof | grep /media/disk
If something important is still open on the disk, make sure to close the files or programs using the disk. If nothing else should be keeping the disk busy, you can usually achieve an unmount with
sudo umount -vl /mnt/external_disk
This performs a verbose, lazy unmount – i.e. Ubuntu unmounts the disk drive when the device is no longer busy, showing any errors in the unmount if there are any.
To confirm that the device has been properly unmounted, use
mount
This will list all the currently mounted devices – your drive should no longer be in the list. If your list is too long or you don’t feel like scanning it mount | grep /media/disk will return nothing if the device has been successfully unmounted.
In case of an unresponsive NFS mount, you can also try
sudo umount -vf /mnt/nameofnfsmount
The -f argument forces an unmount for unresponsive NFS and usually doesn’t help in other cases.
Although umount should perform this automatically, running sync after the unmount can make sure that the file system was properly synced. Happy unmounting!
