Linux Remote Desktop Components

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Remote desktop service components support only desktop systems based on X Display Server. Wayland is currently not supported.
In addition, only the VNC remote desktop protocol is currently supported.

Component Categories

A complete Linux Desktop with remote desktop capabilities consists of the following component categories.

Category	Target	Functionality Provided	Impact If a Problem Occurs	Common Components
Remote Desktop	End Users	Remote desktop interaction and session management	Users cannot use the remote desktop feature	VNC Server, Xrdp
End-User Applications	End Users	Complete specific tasks through a graphical interface	Users cannot use desktop applications	Firefox, Chromium, Thunderbird
Desktop Environment / Window Manager	End Users	Manage graphical applications on the desktop	Desktop interaction is unavailable, including window management such as dragging, minimizing, and maximizing, as well as the Dock, App Indicator, and App Launcher	Common Window Manager options include i3wm and dwm. Common Desktop Environment options include Xfce, KDE Plasma, GNOME, and Cinnamon
Display Backend	Upper-Layer Graphical Applications	Provide interfaces for rendering graphics and receiving/responding to input device events such as the keyboard and mouse	Problems in this layer prevent upper-layer graphical applications from working properly	Xorg, Wayland, XWayland
Hardware Access	Upper-Layer Display Server	Provide interfaces that abstract interactions with hardware	Physical devices cannot work as expected	Input Drivers, framebuffer (fbdev), Direct Rendering Manager (DRM)

VNC Customization

Use the vncserver command provided by the vncserver service to start a remote desktop session.
The platform extends vncserver with several custom features, such as:

• Session isolation: By default, VNC session files are stored in the user's HOME directory. If the HOME directory is located on shared storage, multiple nodes may share the same VNC session, causing conflicts.
  To ensure that the VNC session on each node is isolated, the platform provides custom extensions for vncserver.
• High-resolution support: By default, VNC sessions use a relatively low resolution. The platform extends vncserver so that higher resolutions are supported.

VNC Initialization Process

Use vncserver to initialize a remote desktop session.

A complete remote desktop session includes:

• X Server
• VNC Server
• X Client

X Server Initialization

Use Xtigervnc to initialize the X Server.

Xtigervnc is an X Server that virtualizes a physical display. This means it can output graphics even when no physical display is attached. Graphical applications run as its clients, and their graphical output is rendered on this virtual display.
In addition, it is also a VNC Server, responsible for communicating with the VNC Client so that the session can be accessed and the graphical interface can be rendered.

X Client Initialization

Use the xstartup script to initialize the X Client.

Internally, it calls xinit to start the X Client.

The X Client to be started here includes the desktop management components, because they provide the entry point for end users, who use them to launch desktop applications.
xinit is a script responsible for X Client initialization.
Startup behavior differs between distributions, but the entry point is consistently /etc/X11/xinit/xinitrc.

CentOS (6.9, 7.5)

On CentOS, initialization is delegated to /etc/X11/xinit/Xclients.

It supports only GNOME and KDE.
This means that after either of these desktops is installed, VNC remote desktop can be used without modifying the configuration file.
If another desktop environment is required, manually configure this file by changing the PREFERRED variable to the full binary path of the desired desktop.

Using i3wm as an example, run the following command to modify the configuration file:

sudo sed -i 's/^PREFERRED=.*$/PREFERRED=$(type -p i3)/' /etc/X11/xinit/Xclients

Ubuntu (18.04, 20.04, 22.04)

On Ubuntu, initialization is delegated to /etc/X11/Xsession, which then runs scripts in the /etc/X11/Xsession.d/ directory.

Eventually, the desktop is started through /etc/alternatives/x-session-manager. This file is a symbolic link. Use the following command to check where it points:

readlink /etc/alternatives/x-session-manager
# For example: /usr/bin/gnome-session

After installing the desktop environment, make sure /etc/alternatives/x-session-manager points to the correct desktop startup script.
If the launched desktop is not the expected one, manually update this symbolic link.

Using xfce4 as an example, run the following commands:

sudo rm /etc/alternatives/x-session-manager
sudo ln -s /usr/bin/startxfce4 /etc/alternatives/x-session-manager