X Window System

X Window System provides windowing, graphic display, and device management services to graphic user interface (GUI) applications that run under Linux. X server is the standard implementation of X Window System, and is supported in L4T.
The official X Window System documentation is available on the X.Org Foundation’s X.Org documentation page.
The lightdm or gdm3 service currently is not enabled by default. Therefore, you must start X server manually. This differs from previous releases, in which you could either start X server manually, or make it run by default on the Ubuntu root filesystem started by lightdm or gdm3.

Starting X Server Manually

To start X server
You can define the display configuration in xorg.conf before starting the server. After the server starts, use xrandr to set the runtime configuration. For more information, see Using xrandr for Runtime Configuration.
Enter this command:
$ sudo -b X -ac -noreset -nolisten tcp
The command line arguments may vary depending on platform.
To stop X server
To get the PID of X server, enter this command:
$ ps auX | grep “X”
Then enter this command:
$ sudo kill <pid>

Runtime Configuration

The X server provides several mechanisms for setting configuration and run-time parameters:
Command line options
Environment variables
The configuration files xorg.conf and xorg.conf.d
Fallback defaults
L4T provides utilities for changing the configuration and run-time parameters:
xrandr: A standard X server utility for setting display properties
nvidia-xconfig: An NVIDIA tool that assists in configuring xorg.conf
Customers who support hot plugging of an HDMI™ display must implement an X11 client that reconfigures the HDMI display upon receipt of an RRScreenChangeNotify X11 event. Typically, a gnome-settings-daemon does this.
This solution is required to work around the X11 response to a hot-plugged HDMI display. X11 registers the HDMI output as connected but does not perform an automatic mode-set.

Using xrandr for Runtime Configuration

The NVIDIA® Jetson™ X Driver supports the XRandR 1.2 (X11 Rotate and Resize) extension. This extension allows dynamic enabling, resizing, positioning, and orienting of displays. With the xrandr command line utility, you can control XRandR. That utility is included in the x11-xserver-utils package. The drive-setup.sh installation script installs that package.

Querying Supported Displays and Screen Resolutions

You can use xrandr to get information about supported displays and screen resolutions.
To query attached displays and detect available modes
With X server running, enter this command:
$ xrandr
The output is similar to the following:
Screen 0: minimum 8 X 8, current 2560 X 1600, maximum 16384 X 16384
DP-0 connected primary 2560x1600+0+0 (normal left inverted right X axis y axis) 220mm X 140mm
2560x1600 60.0*+
HDMI-0 disconnected (normal left inverted right X axis y axis)

Obtaining Additional Help

The xrandr utility provides a help menu that lists all supported options and provides guidance on their use.
To get further help and view all available options
Enter this command:
$ xrandr --help

Modifying the Static Configuration (Optional)

The minimal xorg.conf is installed on the target in this location:
Additionally, directories of *.conf fragment files are located in these locations:
By default, xorg.conf contains no specific settings for the screen resolution, virtual desktop size, bit depth, and display select, but instead queries the X driver for the optimum settings based on displays enabled. The Jetson X Driver’s default settings, along with runtime xrandr commands and X server command-line arguments, are meant to be sufficient for most needs. In cases where they are not sufficient, you can configure appropriate settings for screen resolution, bit depth, and display enablement to create custom defaults. You may still use xrandr for runtime manipulation.
NVIDIA recommends that you use the nvidia-xconfig tool to edit the xorg.conf file, rather than edit it by hand. You may have to edit by hand in some circumstances, though.

Using nvidia-xconfig to Configure xorg.conf

The NVIDIA X server configuration tool, nvidia-xconfig, simplifies the task of modifying your xorg.conf file. It parses the file, saves a backup, and modifies the configuration based on your choice of command-line options.

Getting Help with nvidia-xconfig

The nvidia-xconfig tool provides basic and advanced help.
To get help for nvidia-xconfig
To get basic information about the tool, enter the command:
$ nvidia-xconfig --help
To get information about options for modifying xorg.conf, enter:
$ nvidia-xconfig --advanced-help

Specifying a Custom EDID for the Display

The EDID (extended display identification data) is a collection of data in a display which lists its modes of operation (resolutions, refresh rates, etc.).
If X11 does not recognize the mode list of a particular model of display, it may be because the display has an invalid EDID. In this case the X driver cannot accurately determine the capabilities of the display. You can correct this problem by using nvidia-xconfig to specify a valid EDID.
To specify a custom EDID for the display
Enter this command:
$ nvidia-xconfig --custom-edid=HDMI-<n>:<path>
<n> is the index of the HDMI display for which the custom EDID is defined. It is 0 for the first HDMI display, 1 for the second, etc.
<path> is the complete path to a file that contains the custom EDID. The filetype of this file customarily is .bin.

Setting Color Bit-Depth

You can use nvidia-xconfig to set color bit-depth in the xorg.conf file. This makes X11 start with the specified color bit-depth.
To set the color bit-depth
Enter this command:
$ nvidia-xconfig --depth=<depth>
Where <depth> is one of the following supported color bit-depth values: 8, 15, 16, 24, and 30.
For example:
$ nvidia-xconfig --depth=16

Specifying Modes

Use nvidia-xconfig to set a display’s display mode (resolution) in xorg.conf.
To add a mode to the mode list
In a terminal window, enter:
$ nvidia-xconfig -mode=<mode>
Where <mode> is the display mode expressed as X and Y pixels. For example:
$ nvidia-xconfig -mode="1024x768"
If the system has more than one display. You must specify the display whose mode list is to be changed. Enter nvidia-xconfig ‑‑help for information.

Enabling Debug Mode

You can use nvidia-xconfig to enable debug mode in the xorg.conf file. When debug mode is enabled, the X driver logs verbose details about mode validation in the X server log file. You can use this information to troubleshoot mode database issues.
To enable debug mode
Enter this command:
$ nvidia-xconfig -mode-debug
To disable debug mode
Enter this command:
$ nvidia-xconfig -no-mode-debug

Multi-Display X Server Layout

Server layout refers to the number of displays attached to X server, which X screen each display appears on, and the position of each display on its X screen. For example, a server layout might specify that there are two displays, both of which map to one X screen, and display 1 is to the right of display 0 on the X screen.
For single-display systems, the default server layout is sufficient. For multi-display systems you must define your own server layout. NVIDIA X server current supports only a single X screen (a single virtual desktop) mapped to multiple displays.
The default configuration maps a different part of X screen to each display. You can also configure a mirrored layout, which maps the desktop or the same part of the desktop to more than one display. The size of the X screen is the smallest rectangle that covers all of the parts that are mapped to enabled displays.
To enable one X screen (default for span)
Enter this command:
$ nvidia-xconfig -only-one-x-screen
This is an illustration of a one X screen configuration with a side-by-side layout:
Text Description automatically generated
This xrandr command specifies the layout shown above:
$ xrandr --output HDMI-0 --mode 1920x1080 --output DP-0 --mode 1280x1024 --right-of HDMI-0
To enable screen mirroring
Enter this command:
$ nvidia-xconfig --metamode-orientation=clone
To enable screen spanning
Enter this command:
$ nvidia-xconfig --metamode-orientation=<value>
Where <value> specifies the position of display n+1 on the X screen relative to display n:
RightOf (the default)

Configurations that Require Editing xorg.conf

This section describes configuration changes for which you must modify configuration files with a text editor, such as enabling screen saver features, EDID polling, blending, and video overlays.

Enabling Screen Saver Features

By default, X11 features for screen blanking and for suspending and disabling displays are all disabled. You can enable those features by editing this configuration file:

Configuring EDID Polling and Native Resolution

Instead of statically setting the resolution used in the configuration file, the X driver can poll the EDID modes and use each display’s native resolution (usually its highest resolution).
EDID polling is always enabled in the Jetson X Driver. By default, it detects only EDID modes (those reported by the display itself). You can define additional modes as described in Specifying Modes. Remove the added modes to use only modes reported by EDID.

Enabling Blending and Video Overlays

TegraOverlayPriority is a .conf file setting that controls overlay stacking order. Its range is 0 to 255 inclusive, and the default is 255. Larger numbers represent greater depths; thus an overlay with priority 0 is in front of all others, and 255 is behind all others. The value has no meaning when only one overlay is present on the display.
TegraOverlayBlendmode determines how an X overlay is combined with another overlay behind it during scanout. The possible modes are:
Opaque (default)
This value has meaning only when an external process has created a display that is behind the X server.
To set blending and video overlay attributes
In the Device section of xorg.conf, add a setting in the following form:
Option "MetaModes" "<mode_name> { <property> = <value>,... <setting> = <value> }"
<mode_name> specifies the name of the mode whose overlay attributes are to be set. If no <mode_name> is specified, it defaults to nvidia-auto-select.
<property> is the name of a mode property, and <value> is its new value.
This is an example of a complete setting:
Option "MetaModes" "nvidia-auto-select { TegraOverlayBlendmode = PremultSourceAlphaBlend, TegraOverlayPriority = 0 }"
These properties are per-output and can also be queried and modified during run-time via xrandr. To specify a particular display in a multi-display system, use the ‑‑output option. For more information enter the command xrandr ‑q.
To query the blending and video overlay values
Enter this command:
$ xrandr --prop
To modify the blending and video overlay properties
Enter these commands:
$ xrandr --output HDMI-0 --set TegraOverlayPriority 0
$ xrandr --output HDMI-0 --set TegraOverlayBlendmode PremultSourceAlphaBlend
X window system does not support alpha blending, so all alpha blending on the enabled display must be done through OpenGL ES rendering. Alpha blending for natively rendered pixels is undefined.