I got these error messages when trying to unmount /dev/sda3

I got these error messages when trying to unmount /dev/sda3.

root@marudhu:~# umount -t /dev/sda3
umount: bad usage
Try 'umount --help' for more information.
root@marudhu:~# umount -t/dev/sda3
umount: bad usage
Try 'umount --help' for more information.
root@marudhu:~#

From man umount :

-t, --types type...
              Indicate that the actions should only be taken on filesystems of
              the  specified  type.

You haven't specified a filesystem after the -t flag. Use the following command that doesn't have the optional -t flag in it. Also you don't need to be root user to run the following command if you preface the same command with sudo instead as follows:

sudo umount /dev/sda3