Question: minicom device /dev/ttyusb0 is locked?
Answer: Sometimes if the connection to a device via Minicom is lost, the next time you start Minicom you could see an error: Device /dev/ttyS0 is locked. The name /dev/ttyS0 may be different, depending on your COM port. To avoid this issue you should always shut down Minicom using CTRL+A keys and then the Q key.