Even when the I2C ports on the Raspberry Pi are enabled as described here, they are only accessible when running in supervisor mode, which is not terribly convenient. To fix that, it’s possible to add a udev rule to change the mode of the devices. The description here is borrowed from my friend at Jumpnow incidentally.
Create a file /etc/udev/rules.d/90-i2c.rules and add the line:
Reboot the Pi and then the I2C ports will be accessible without having to run stuff with sudo.