Permission denied opening serial USB port

[barry manilow]

Just installed Weewx 5 and new install of Bookworm 32 bit on Raspberry pi 4. I'm using a USB Serial interface with my Davis Vantage Vue, which has worked perfectly for the past few years.

After completing setup I started with sudo service weewx start. 

No data appeared to be sent, so checked weewx status and got this error:

 $ sudo service weewx status
× weewx.service - WeeWX
     Loaded: loaded (/lib/systemd/system/weewx.service; enabled; preset: enabled)
     Active: failed (Result: exit-code) since Wed 2024-06-05 16:07:17 BST; 53s ago
   Duration: 299ms
       Docs: https://weewx.com/docs
    Process: 1733 ExecStart=weewxd /etc/weewx/weewx.conf (code=exited, status=4)
   Main PID: 1733 (code=exited, status=4)
        CPU: 299ms

Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL weewx.engine:     ****                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL weewx.engine:     ****    File "/usr/lib/python3/dist-packages/serial/serialutil.py", line 244, in __init__
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL weewx.engine:     ****      self.open()
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL weewx.engine:     ****    File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 325, in open
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL weewx.engine:     ****      raise SerialException(msg.errno, "could not open port {}: {}".format(self._port, msg))
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL weewx.engine:     ****  serial.serialutil.SerialException: [Errno 13] could not open port /dev/ttyUSB0: [Errno 13] Permission denied: '/dev/ttyUSB0'
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL __main__: Unable to load driver: [Errno 13] could not open port /dev/ttyUSB0: [Errno 13] Permission denied: '/dev/ttyUSB0'
Jun 05 16:07:17 raspberrypi weewxd[1733]: CRITICAL __main__:     ****  Exiting...
Jun 05 16:07:17 raspberrypi systemd[1]: weewx.service: Main process exited, code=exited, status=4/NOPERMISSION
Jun 05 16:07:17 raspberrypi systemd[1]: weewx.service: Failed with result 'exit-code'

Something has changed with permissions I think, but no idea what.

Any ideas on what has happened? Thanks!

[Pierre-Yves]

Hi Barry,

Maybe you should look at https://github.com/weewx/weewx/wiki/Understanding-permissions

PY

[vince]

Did you even try to look for the answer to this very frequently asked question ?

Please use the 'search conversations within weewx-user' box at the top of the browser and look for your exact error message "serial.serialutil.SerialException: [Errno 13] could not open port /dev/ttyUSB0: [Errno 13] Permission denied: '/dev/ttyUSB0'"

Any of the top five returned results provide the answer.   My answer from March to somebody else in https://groups.google.com/g/weewx-user/c/duGfSg6cQZ4/m/adiOz1FUAAAJ provides links to the why.

ALWAYS ALWAYS ALWAYS SEARCH FOR YOUR EXACT ERROR MESSAGE.   The odds are very very high that it has been asked and answered here before.

[barry manilow]

Yes, it was a permissions issue. Thanks for the info.

I checked serial/USB adapter permissions using

ls- l /dev/ttyS0

and added weewx to the dialout group

sudo usermod -aG dialout weewx