On Linux, the USB-CEC Adapter appears as a serial device at /dev/ttyACM0. If your user account does not have permission to access this device, cec-client will fail with a permission error even though the adapter is correctly detected by the system.
Symptom
When running cec-client or attempting to use the adapter through Kodi, you see an error such as:
error opening serial port '/dev/ttyACM0': Permission denied
or in Kodi:
Couldn't initialise CEC adapter
The adapter is visible in lsusb output and cec-client -l lists it, but attempting to connect fails.
Cause
The /dev/ttyACM0 device is owned by the dialout group on most Linux distributions. Your user account — or the account Kodi runs under — has not been added to this group and therefore cannot open the device.
Fix — Add User to the dialout Group
Run the following command, replacing username with your actual Linux username:
sudo usermod -aG dialout username
Then log out and log back in. The group membership change does not take effect until you start a new session — simply opening a new terminal window is not sufficient.
To confirm the change has taken effect, run:
groups
dialout should appear in the list. Then retry cec-client or restart Kodi.
dialout group, not just your own login account.Alternative — udev Rule
If you prefer not to add a user to the dialout group, you can create a udev rule to grant the correct permissions to the adapter directly. Create a file at /etc/udev/rules.d/99-cec.rules with the following content:
SUBSYSTEM=="tty", ATTRS{idVendor}=="2548", ATTRS{idProduct}=="1002", MODE="0666"Then reload udev rules:
sudo udevadm control --reload-rules sudo udevadm trigger
Unplug and replug the adapter. The device will now be accessible by all users without requiring group membership.