Ubuntu Manpage: ddcutil - Query and change monitor settings

NAME

       ddcutil - Query and change monitor settings

SYNOPSIS

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

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

DESCRIPTION

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(which have been replaced by more descriptive names), experimental options, and options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.

RESTRICTIONS

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

COMMANDS

Primary Commands
These are the most used ddcutil commands.

detect Find monitors that have a Virtual Control Panel.

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.

capabilities
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.

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 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.

scs 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.

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

discard all|capabilities|dsa cache[s]
Discard cached files used for performance improvement.

traceable-functions
Lists functions that can be specifically traced using an option like --trcfunc or
--trcfrom

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

environment
Probe the ddcutil installation environment.

usbenv Probe USB aspects of the ddcutil installation environment.

probe Explore the capabilities and features of a single monitor.

interrogate
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.

COMMAND ARGUMENTS

       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|KNOWN
              All feature codes understood by ddcutil
       COLOR  Scan color related feature codes
       PROFILE
              Subset  of  color  related feature codes that are saved and restored by dumpvcp and
              loadvcp
       SCAN   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

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)
-b,--bus
bus-number I2C bus number
--hiddev
device number hiddev device number
-u,--usb busnum.devicenum
USB bus and device numbers
-g,--mfg
3 letter manufacturer code
-l,--model
model name
-n,--sn
serial number. (This is the "serial ascii" field from the EDID, not the binary
serial number.)
-e,--edid
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.
-V, --version
Show program version.
--settings
Report option settings in effect.
-h,--help
Show program help.
--hh Show program help including hidden options. Hidden options include alternative
option names, experimental and deprecated options, and ones for debugging.

Options for diagnostic output
--ddcdata
Reports DDC protocol errors. These may reflect I2C bus errors, or deviations by
monitors from the MCCS specification. Formerly named --ddc,
--stats [all|errors|tries|calls|elapsed|time]
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.
--vstats [all|errors|tries|calls|elapsed|time]
Like --stats, but includes per-display statistics.
--istats [all|errors|tries|calls|elapsed|time]
Like --vstats, but includes additional internal information.
--syslog [debug|verbose|info|notice|warn|error|never ]
Write messages of the specified or more urgent severity level to the system log.
The ddcutil default is WARN. The libddcutilP default is NOTICE.
--libddcutil-trace-filefilename
Direct trace output to the specified file instead of the terminal. This is a
libddcutil only option.
--tracetrace-class-name
Trace all functions in a trace class. For a list of trace classes, use --help
--verbose.
--trcfuncfunction-name
Trace a specific function.

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-dynamic-sleep, --disable-dynamic-sleep
Dynamically adjust the sleep-multiplier over multiple ddcutil invocations,
improving performance. The default is --enable-dynamic-sleep
--min-dynamic-multiplier decimal number
Modify the dynamic sleep algorithm to never adjust the sleep multiplier below this
value. This option can help dampen swings in sleep multiplier values.
--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. In general, newer option --enable-
dynamic-sleep will provide better performance.
--lazy-sleep
Peform mandated sleeps before the next DDC/CI operation instead of immediately
after the DDC/CI operation that specified a delay, marginally improving
performance.
--ddc-checks-async-min
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
--skip-ddc-checks
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-cache [capabilities|dsa|all
Discard cached display information and/or dynamic sleep data.

Options that modify behavior
--maxtries (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 communication with the
Virtual Control Panel. (These options are available only if ddcutil was built with
USB support.) The default is --disable-usb
--ignore-usb-vid-pid vid:pid
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. 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.
--force-slave-address
Take control of slave addresses on the I2C bus even they are in use. Has use only
with file-io, not with ioctl-io.
--enable-cross-instance-locks | --disable-cross-instance-locks
Coordinates /dev/i2c device access across multiple instance of ddcutil and
libddcutil. The default is --enable-cross-instance-locks
--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.
--i2c-source-addr hex-addr
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.
--permit-unknown-feature
Allow setvcp of unknown features.

--noconfig
Do not process the configuration file

NVIDIA PROPRIETARY DRIVER

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

VIRTUAL MACHINES

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

EXAMPLES

       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.

DIAGNOSTICS

       Returns 0 on success, 1 on failure.

       Requesting help is regarded as success.

AUTHOR

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

                                            2024-01-11                                 ddcutil(1)