CEC Adapter — Linux Permission Denied on /dev/ttyACM0

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.

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.

Related Articles

• CEC Adapter — Linux Setup
• CEC Adapter — Raspberry Pi
• Getting Started with the USB-CEC Adapter