I am sure this is a Linux issue per se. This problem has been replicated across three different flavors of Linux on my Ubuntu Macbook Pro. Mavproxy does not have permission to access the serial port. Manually adding the user account to the tty and dialout groups make no difference.
Not sure what the /dev/serial/by-id/ is about either and why it is not a tty port.
WARNING: You should uninstall ModemManager as it conflicts with APM and Pixhawk
Auto-detected serial ports are:
Connecting to /dev/serial/by-id/usb-ArduPilot_mRoX21_370044001051353336333832-if00
Connect /dev/serial/by-id/usb-ArduPilot_mRoX21_370044001051353336333832-if00 source_system=255
Failed to connect to /dev/serial/by-id/usb-ArduPilot_mRoX21_370044001051353336333832-if00 : [Errno 13] could not open port /dev/serial/by-id/usb-ArduPilot_mRoX21_370044001051353336333832-if00: [Errno 13] Permission denied: ‘/dev/serial/by-id/usb-ArduPilot_mRoX21_370044001051353336333832-if00’
No mode mapping available
Telemetry log: mav.tlog