umount - it is used to unmounts a mounted filesystem, informing the system to complete any pending read or write operations, and safely detaching it

To unmount all the filesystems mentioned in /etc/mtab $ sudo umount -a

To forcefully unmount a filesystem $ sudo umount -f /backup

To lazy unmount of a filesystem $ sudo umount -l /backup

To unmount a Partition or Filesystem $ sudo umount /mnt

To recursively unmount a target with all its children $ sudo umount -R /mnt

To umount without writing in /etc/mtab $ sudo umount -n /mnt

To unmount more than mount point in a single execution $ sudo umount /mnt /backup

regards, T.Dhanasekar