unable to open /dev/sdb

As an AI language model, I cannot determine the exact reason why you are unable to open /dev/sdb. However, I can provide you with some possible solutions that you can try:

1. Check if the device is properly connected: Ensure that the device is properly connected to your computer and is receiving power.

2. Check if the device is mounted: Check if the device is mounted by running the command "mount | grep sdb". If it is mounted, unmount it using the "umount" command.

3. Check the file system: Check the file system of the device by running the command "sudo fdisk -l". If the file system is not recognized, try formatting the device.

4. Check permissions: Check if you have the necessary permissions to access the device. Run the command "ls -l /dev/sdb" to check the permissions.

5. Check for hardware issues: If none of the above solutions work, there might be a hardware issue with the device. Try connecting the device to another computer to see if it works.