Can't open /dev/sdb1 exclusively. Mounted filesystem?

This error message suggests that the device `/dev/sdb1` is already mounted and in use by another process, preventing you from accessing it exclusively.

To resolve this issue, you will need to unmount the device first before attempting to access it exclusively. You can do this by running the following command:

umount /dev/sdb1

If the device is still in use by another process, you may need to identify the process and terminate it before you can unmount the device. You can use the `fuser` command to identify the process that is using the device, and then terminate it using the `kill` command.

Once you have unmounted the device, you should be able to access it exclusively without encountering the error message.