1. Reasons

Generally, it is not the root user and has no permission on the port.

2. Solutions

2.1 temporary

1 sudo chmod 777 /dev/ttyUSB0

Modify the permission to be readable, writable and executable. However, this problem will occur again when this setting is restarted and used next time. You need to reset it again.

2.2 permanent

1 sudo usermod -aG dialout usrname

Usrname: user name.

That is, the user name is added to the dialout user group. After restart, it can be used directly.