When opening a serial port to access a Z-Wave controller, the library may indicate an error such as:

Cannot open serial port /dev/ttyUSB0: Permission denied

On Linux machines, this is often due to the fact that, to control serial ports, the user must be a member of the “dialout” group.

Edit /etc/group to add the user to this group, then log out and log back in to make this group membership effective.