ddcutil - Query and change monitor settings



ddcutil − Query and change monitor settings


ddcutil [options] command [command-arguments] [options]

Options can be written either before or after the command and its arguments.


ddcutil is used to query and change monitor settings.

ddcutil communicates with monitors that implement the Monitor Control Command Set (MCCS) using the DDC/CI protocol on an I2C bus. Normally, the video driver for the monitor exposes the I2C bus as devices named /dev/i2c-n. Alternatively, ddcutil can communicate with monitors that use USB to communicate MMCS, provided the monitors meet 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.

The monitor settings that can be controlled by ddcutil are, generally speaking, those that 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 describes ddcutil commands and options most important to the typical user. For complete documentation, use the --help option or see the web site http://www/ddcutil.com.


ddcutil does not support laptop monitors, which do not implement DDC/CI.


Primary Commands

These are the most used ddcutil commands.


"Report monitors"

vcpinfo [ feature-code | feature-group ]

Describe VCP feature codes. as defined in the MCCS specification. Use option --verbose to see values for Non-Continuous features.


Query the monitor’s capabilities string

getvcp [ feature-code | feature-group ] ...

Report a VCP feature value, or a group of feature values. More than one feature code can be specified. However feature codes and groups cannot be combined.

setvcp feature-code [+|-] new-value ...

Set a VCP feature value. If + or - is specified, it must be surrounded by blanks, and indicates a relative value change of a continuous VCP feature. Multiple feature/value pairs (with or without [+|1]) can be specified.

Secondary Commands

These commands address special situations.

Save color profile related VCP feature values in a file. If no file name is specified, one is generated and the file is saved in $HOME/.local/share/ddcutil,

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.


Issue DDC/CI Save Current Settings request. Most monitors do not implement this command. A few require it for values changed by setvcp to take effect.


Tests if a hiddev device may be a USB connected monitor, for use in udev rules.

Diagnostic commands

These commands diagnose issues in the system configuration that affect ddcutil operation, and that gather information for remote problem diagnosis.

Probe the ddcutil installation environment.


Probe USB aspects of the ddcutil installation environment.


Explore the capabilities and features of a single monitor.


Collect maximum information for problem diagnosis. Includes the output of ddcutil environment --verbose andfor each detected monitor, the output of ddcutil capabilities --verbose and ddcutil probe --verbose.



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. 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".


Normally, this is a decimal number in the range 0..255, or a hexadecimal number in the range x00..xff. More generally, this is actually a two byte value, i.e. x00..xffff, and a few features on some monitors use this extended range.


Options for monitor selection. If none are specified, the default is the first detected monitor. Options --mfg, --model and --sn can be specified together.
-d , --dis , --display

display-number logical display number (starting from 1)


bus-number I2C bus number


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.

Feature selection filters
-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.

Options that 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

Options for program information.

Show program help.

-V, --version

Show program version.


Report option settings in effect.

Options for diagnostic output


Reports DDC protocol errors. These may reflect I2C bus errors, or deviations by monitors from the MCCS specification.

[--stats|--vstats] [all|errors|tries|calls|elapsed|time]

Report execution statistics.
I2C bus communication is an inherently unreliable. It is the responsibility of the program using the bus, i.e. ddcutil, to manage retries in case of failure. This option reports retry counts and various performance statistics. If no argument is specified, or ALL is specified, then all statistics are output. ELAPSED is a synonym for TIME. CALLS implies TIME.

--vstats [all|errors|tries|calls|elapsed|time]

Like --stats, but includes per-display statistics.

--syslog[ debug|verbose|info|notice|warn|error|never ]

Write messages of the specified or more urgent severity level to the system log. The default is WARN.

Options that tune execution
--enable-capabilities-cache, --disable-capabilities-cache

Enable or disable caching of capabilities strings, improving performance. The default is --enable-capabilities-cache

--enable-displays-cache, --disable-displays-cache

Enable or disable caching of information about detected displays, improving performance. The default is --enable-displays-cache

--sleep-multiplier decimal number

Adjust the length of waits listed in the DDC/CI specification by this number to determine the actual wait time. Well behaved monitors work with sleep-multiplier values less than 1.0, while monitors with poor DDC implementations may require sleep-multiplier values greater than 1.0.

--enable-dynamic-sleep, --disable-dynamic-sleep

Dynamically adjust the sleep-multiplier over multiple ddcutil invocations, improving performance. The default is --enable-dynamic-sleep


If there are several monitors, initial checks are performed in multiple threads, improving performance.


Peform mandated sleeps before the next DDC/CI operation instead of immediately after the DDC/CI operation that specified a delay, marginally improving performance.

Options that modify behavior
(max-read-tries, max-write-read-tries, max-multi-part-tries)

Adjust the number of retries. A value of "." or "0" leaves the setting for a retry type unchanged.

--verify | --noverify

Verify or do not verify values set by setvcp or loadvcp. --noverify is the default.

--mccs MCCS version

Tailor command input and output to a particular MCCS version, e.g. 2.1

--enable-udf, --disable-udf

Enable or disable support for user supplied feature definitions. The default is --enable-udf

--enable-usb, --disable-usb

Enable or disable support for monitors that implement USB commuincation with the Virtual Control Panel. (These options are available only if ddcutil was built with USB support.) The default is --disable-usb


Force ddcutil to ignore a particular USB device, specified by its 4 hex digit vendor id and its 4 hex digit product id.

--ignore-hiddev hiddev-device-number

Force ddcutil to ignore a particular USB device, specified by /dev/usb/hiddev device number

--use-file-io | --use-ioctl-io

Cause ddcutil to use the write()/read() interface or the ioctl interface of driver dev-i2c to send and receive I2C packets. By default, ddcutil uses the ioctl interface. Depending on how the Nvidia proprietary driver was built, this can fail, in which case ddcutil switches to using the file io interface.


Take control of slave addresses on the I2C bus even they are in use. Has use only for the proprietary Nvidia video driver.

--edid-read-size 128|256

Force ddcutil to read the specified number of bytes when reading the EDID. This option is a work-around for certain driver bugs. The default is 256.


Requires read/write access to /dev/i2c devices. See http://www.ddcutil.com/i2c_permissions


Some Nvidia cards using the proprietary Nvidia driver require special settings to properly enable I2C support. See http://www.ddcutil.com/nvidia.


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: http://www.ddcutil.com


Sanford Rockowitz (rockowitz at minsoft dot com)
Copyright 2015−2023 Sanford Rockowitz

Updated 2024-01-29 - jenkler.se | uex.se