I2C Device Permissions

ddcutil requires read/write access to /dev/i2c devices, or more precisely all /dev/i2c devices associated with video cards. It can, of course, be run as root.

(For USB devices, see USB Device Permissions).

Starting with release 1.4.0, ddcutil installed udev rule 60-ddcutil.rules that grants read/write access to the logged on user.

As of release ddcutil 2.0, this has changed to files 60-ddcutil-i2c.rules and 60-ddcutil-usb.rules.

Granting I2C Device Permissions on Versions Prior to 1.4.0

The simplest way to grant I2C device permissions on versions prior to 1.4.0 is to manually install file /etc/udev/rules.d/60-ddcutil-i2c.rules:

SUBSYSTEM=="i2c-dev", KERNEL=="i2c-[0-9]*", ATTRS{class}=="0x030000", TAG+="uaccess"
SUBSYSTEM=="dri", KERNEL=="card[0-9]*", TAG+="uaccess"

Granting I2C Device Permissions using group i2c.

The original method for granting /dev/i2c device permissions relied on group i2c. These instructions are retained for reference, in case they are useful for some corner cases.