ddcutil(1) General Commands Manual ddcutil(1)

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. The 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 settings vary from monitor to monitor.

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.

Common use cases include changing monitor brightness and color. Using scripts, the changes can be effected by keystrokes, or in response to the time of day. Another common use case is to switch the monitor input source.

A more complex 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.

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. If option --verbose is specifeid in conjunction with --help, more extensive help on option arguments is shown.

Option --hh shows all options recognized by ddcutil. These include deprecated option names (which have been replaced by more descriptive names), experimental options, and options only of interest to developers.

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

These are the most used ddcutil commands.

Find monitors that have a Virtual Control Panel.
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
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.
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.

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,
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.
Discard cached files used for performance improvement.
Lists functions that can be specifically traced using an option like --trcfunc or --trcfrom

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.

feature-code

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

feature-group

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".

new-value

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.

display-number logical display number (starting from 1)
bus-number I2C bus number
device number hiddev device number
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

Normally, getvcp does not report unsupported features when querying a feature-group. This option forces output.
Normally, getvcp does not report Table type features when querying a feature-group. --show-table forces output. --no-table is the default.
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.

Show brief detail. For command getvcp, the output is in machine readable form.
Show extended detail

Options for program information.

Show program version.
Report option settings in effect.
Show program help.
Show program help including hidden options. Hidden options include alternative option names, experimental and deprecated options, and ones for debugging.

Options for diagnostic output

Reports DDC protocol errors. These may reflect I2C bus errors, or deviations by monitors from the MCCS specification. Formerly named --ddc,
Report execution statistics. I2C bus communication is 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.
Like --stats, but includes per-display statistics.
Like --vstats, but includes additional internal information.
Write messages of the specified or more urgent severity level to the system log. The ddcutil default is WARN. The libddcutilP default is NOTICE.
Direct trace output to the specified file instead of the terminal. This is a libddcutil only option.
Trace all functions in a trace class. For a list of trace classes, use --help --verbose.
Trace a specific function.

Options that tune execution

Enable or disable caching of capabilities strings, improving performance. The default is --enable-capabilities-cache
Dynamically adjust the sleep-multiplier over multiple ddcutil invocations, improving performance. The default is --enable-dynamic-sleep
Modify the dynamic sleep algorithm to never adjust the sleep multiplier below this value. This option can help dampen swings in sleep multiplier values.
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. In general, newer option --enable-dynamic-sleep will provide better 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.
If there are several monitors, initial DDC checks are performed in multiple threads, improving performance. This option was formerly (and ambiguously) named --async. The default is --ddc-checks-async-min 3
Assume DDC communication works and monitors properly use the invalid feature flag in a DDC/CI Reply packet to indicate an unsupported feature, improving display detection performance.
Discard cached display information and/or dynamic sleep data.

Options that modify behavior

Adjust the number of retries. A value of "." or "0" leaves the setting for a retry type unchanged.
Verify or do not verify values set by setvcp or loadvcp. --noverify is the default.
Tailor command input and output to a particular MCCS version, e.g. 2.1
Enable or disable support for user supplied feature definitions. The default is --enable-udf
Enable or disable support for monitors that implement USB communication 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.
Force ddcutil to ignore a particular USB device, specified by /dev/usb/hiddev device number
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. Nvidia proprietary driver are built in a way such that the ioctl interface 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 with file-io, not with ioctl-io.
Coordinates /dev/i2c device access across multiple instance of ddcutil and libddcutil. The default is --enable-cross-instance-locks
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.
Use this as the source address in DDC packet, instead of the normal value. This option has been found to enable access some control functions when using some displays, particularly from LG.
Allow setvcp of unknown features.

Do not process the configuration file

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

2024-01-11