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ddcutil(1) General Commands Manual ddcutil(1)


ddcutil - Query and change monitor settings


ddcutil [--adl|-a adapter-index.display-index] [--async] [--bus|-b busno] [--ddc] [--display|--dis|-d dispno] [--edid 256 hex character EDID] [--excp] [-f|--force] [--force-slave-address] [--hiddev hiddevdevicenumber] [--mfg|-g manufacturer code] [--maxtries (comma-separated-list)] [--model|-l model name] [--nodetect] [--sn|-n serial number] [ --rw | --ro | --wo] [--show-table|--no-table] [-s|--stats [stats-class]] [-t|--terse|--brief|-v|--verbose] [-U|--show-unsupported] [--usb|-u busnum.devicenum] [--verify | --noverify] [-V|--version] [h|--help] detect | capabilities | scs | probe | getvcp [feature-code|feature-group] |setvcp feature-code new-value ] | vcpinfo [feature-code|feature-group] | dumpvcp [filename] | loadvcp filename ] | environment | usbenvironment'| interrogate


ddcutil is used to query and change monitor settings.

ddcutil communicates with monitors implementing MCCS (Monitor Control Command Set) using the DDC/CI protocol on the I2C bus. Normally, the video driver for the monitor exposes the I2C bus as devices named /dev/i2c-n. Alternatively, ddcutil can communicate with USB connected monitors implementing the USB Monitor Control Class Specification.

The Monitor Control Command Set describes a collection of Virtual Control Panel (VCP) features that a monitor can implement. Each feature is identified using a single byte. For example, feature x10 is the brightness control.

In general, the monitor settings that can be controlled by ddcutil are a superset of what can be changed using the buttons on a monitor and its on screen display. The specific capabilities vary from monitor to monitor.

A particular use case for ddcutil is as part of color profile management. Monitor calibration is relative to the monitor color settings currently in effect, e.g. red gain. ddcutil allows color related settings to be saved at the time a monitor is calibrated, and then restored when the calibration is applied.

Another common use case is to switch the monitor input source.

This man page includes only abbreviated documentation of trace and other program diagnostic facilities.

For extended documentation, use the "--help" option, and see


detect Report monitors
vcpinfo [ feature-code | feature-group ]
Describe VCP feature codes that ddcutil knows how to interpret
Query the monitor's capabilities string
getvcp [ feature-code | feature-group ]
Report a single VCP feature value, or a group of feature values
setvcp [+|-] feature-code new-value
Set a single VCP feature value. If + or - is specified, it must be surrounded by blanks, and indicates a relative value change of a Continuous VCP feature.
dumpvcp filename
Save color profile related VCP feature values in a file. If no file name is specified, one is generated and the file is saved <describe location>
loadvcp filename
Set VCP feature values from a file. The monitor to which the values will be applied is determined by the monitor identification stored in the file. If the monitor is not attached, nothing happens.
Probe the ddcutil installation environment.
Issue DDC/CI Save Current Settings request.
Probe USB aspects of the ddcutil installation environment.
Explore the capabilities and features of a single monitor.
Collect maximum information for problem diagnosis.
Tests if hiddev device is a USB connected monitor, for use in udev rules.



A feature-code is specified by its 2 character hex feature number, with or without a leading "0x", e.g. 0x10, 10


The following are the most useful feature groups recognized. For a complete list, use the --help option.

All feature codes understood by ddcutil
Scan color related feature codes
Subset of color related feature codes that are saved and restored by dumpvcp and loadvcp
Scan all possible feature codes 0x00..0xff, except those known the be write-only

Feature group names can be abbreviated to the first 3 characters. Case is ignored. e.g. COL, pro


A decimal number in the range 0..255, or hexadeciaml number in the range x00..xff.


Options for monitor selection. If none are of these options are specified, the default is the first detected monitor. Options --mfg, --model and --sn can be specified together.
display-number logical display number (starting from 1)
bus-number I2C bus number
-a,--adl adapterIndex.displayIndex
ADL adapter and display indexes
device number hiddev device number
-u,--usb busnum.devicenum
USB bus and device numbers
3 letter manufacturer code
model name
serial number. (This is the "serial ascii" field from the EDID, not the binary serial number.)
256 hex character representation of the 128 byte EDID. Needless to say, this is intended for program use.

Options to control the amount and form of output.

-t, --terse, --brief
Show brief detail. For command getvcp, the output is in machine readable form.
-v, --verbose
Show extended detail
-U, --show-unsupported
Normally, getvcp does not report unsupported features when querying a feature-group. This option forces output.
--show-table | --no-table
Normally, getvcp does not report Table type features when querying a feature-group. --show-table forces output. --no-table is the default.
--rw, --ro, --wo
Limit getvcp or vcpinfo output to read-write, read-only, or (for vcpinfo) write-only features.
--mccs MCCS version
Tailor vcpinfo output to a particular MCCS version, e.g. 2.1

Options for diagnostic output.

--stats [all|errors|tries|calls|elapsed|time]
Report execution statistics. If no argument is specified, or ALL is specified, then all statistics are output. elapsed is a synonym for time. calls implies time.
I2C bus communication is an inherently unreliable. It is the responsibility of the program using the bus to manage retries in case of failure. This option reports retry counts and various performance statistics.
Reports DDC protocol errors. These may reflect I2C bus errors, or deviations by monitors from the MCCS specification.

Options for program information.

Show program help.
-V, --version
Show program version.

Options to tune execution:

--maxtries (max-read-tries, max-write-read-tries, max-multi-part-tries)
Adjust the number of retries
Take control of slave addresses on the I2C bus even they are in use.
-f, --force
Do not check certain parameters.
Verify values set by setvcp or loadvcp. (default)
Do not verify values set by setvcp or loadvcp.
If there are multiple monitors, initial checks are performed in multiple threads, improving performance.
If the monitor is specified by its I2C bus number (option --busno) skip the monitor detection phase, improving performance.


Requires read/write access to /dev/i2c devices. See


Some newer Nvidia cards (e.g. GTX660Ti) require special settings to properly enable I2C support. If you are using this driver and ddcctool does not work with your Nvidia card (TODO: Describe symptoms), you can try the following:

Copy file /usr/local/share/ddcutil/data/90-nvidia-i2c.conf to directory /etc/X11/xorg.conf.d

sudo cp /usr/local/share/ddcutil/data/90-nvidia-i2c.conf /etc/X11/xorg.conf.d

This file will work "out of the box" if you do not have an /etc/X11/xorg.conf file. If you do, adjust the Identifier value in the file to correspond to the value in the master xorg.conf file.

(Note that the above instructions assume that datadir was set to /usr/local/share when ddcutil was installed. YMMV)

For further discussion of Nvidia driver settings, see


AMD's proprietary video driver fglrx does not expose the I2C bus. Instead, it provides access to the bus through the AMD Display Library, aka ADL. Owing to copyright restrictions, the ADL header files are not distributed with the ddcutil source. Additional steps are required to build ddcutil with fglrx support.

To see if your copy of ddcutil was built with fglrx support, issue the command:
ddcutil --version

ADL identifies monitors using an adapter-number/display-number pair. To select a monitor using these numbers, specify the --adl option with a period separating the adapter-number and display-number, e.g.
--adl 0.1


Virtualized video drivers in VMWare and VirtualBox do not provide I2C emulation. Use of normal video drivers with PCI passthrough is possible.


ddcutil detect

Identify all attached monitors.

ddcutil getvcp supported

Show all settings that the default monitor supports and that ddcutil understands.

ddctpp getvcp 10 --display 2
Query the luminosity value of the second monitor.

ddcutil setvcp 10 30 --bus 4

Set the luminosity value for the monitor on bus /dev/i2c-4.

ddcutil vcpinfo --verbose

Show detailed information about VCP features that ddcutil understands.

ddcutil interrogate > ~/ddcutil.out

Collect maximum information about monitor capabilities and the execution environment, and direct the output to a file.


Returns 0 on success, 1 on failure.

Requesting help is regarded as success.


The project homepage:


Sanford Rockowitz (rockowitz at minsoft dot com)
Copyright 2015-2018 Sanford Rockowitz

01 April 2018