The error message indicates that the avrdude program doesn't have the necessary permissions to access the /dev/ttyUSB0 device. This is a common issue when working with serial devices on Linux. Here are a few steps you can take to resolve this issue:

1. Add Your User to the dialout Group

Serial devices in Linux are often owned by the dialout group. Adding your user to this group will give you the necessary permissions to access the device.

  1. Open a terminal.
  2. Add your user to the dialout group:
sudo usermod -aG dialout $USER
  1. Log out and log back in for the changes to take effect.

2. Change the Ownership of the Device

If you need a temporary solution, you can change the ownership of the device to your user. Note that this change will be reverted after a reboot.

  1. Open a terminal.
  2. Change the ownership of /dev/ttyUSB0:
sudo chown $(whoami) /dev/ttyUSB0

3. Use sudo to Run avrdude

As a last resort, you can run avrdude with sudo to temporarily gain the necessary permissions. This is not recommended for regular use due to security implications.

  1. Open a terminal.
  2. Run avrdude with sudo:
sudo avrdude -v -p atmega328p -c arduino -P /dev/ttyUSB0 -b 115200 -U flash:w:your_sketch.hex

4. Verify the Device Path

Ensure that /dev/ttyUSB0 is the correct path for your device. Sometimes, the device might be listed under a different path such as /dev/ttyACM0.

  1. Open a terminal.