Comment by Mike Scheutzow for The linux account you are using to run ROS probably does not have read-write permission for the device /dev/i2c-0. As a quick hack, you can issue this command:sudo chmod 666 /dev/i2c-0but this will need to be repeated if you reboot the machine.The better thing to do is to create a udev rule which will change the permissions on this device each time the machine boots.