This post outlines the process of installing the XFCE desktop environment and configuring a VNC server for remote graphical access on an Ubuntu 22.04 server without a monitor. For a foundational understanding of the X Window System, refer to the earlier blog Understanding and using the X Window System.

XFCE Desktop Environment

XFCE is a lightweight desktop environmnet ideal for low-resource computing infrastructure like lightweight VMs in the cloud. Similarly, tigervnc is a lightweight X-Server suitable for VMs to access the XFCE desktop remotely.

Install the XFCE desktop environment and the VNC server

$ sudo apt install xfce4 xfce4-goodies tigervnc-standalone-server

In most linux distros, the package is called tigervnc-server. After installing the server, a user needs to create a password.

$ vncpasswd

This will create a directory ~/.vnc with all config, log and process files for the VNC server. If it does not exist, create a config file ~/.vnc/config with some example parameters.

geometry=1024x768
localhost=no

The geometry options set the xfce desktop size on your remote desktop. In some default installation, the vncserver starts with the localohost=yes option that will not accept any connections from outside.

Opening Ports in Firewall

The TCP port utilized by the VNC server is decided by the server’s starting display number. Without a specified display number, the server defaults to the lowest free one. VNC connections occur on port 5900+ display. Here, choosing display number :1 means connecting to remote port 5901. Typically, you might need to allow port access via the firewall. The commands will depend on the linux distro.

ufw allow 5901/tcp

Setting up xstartup

Create (if does not exist) and add the following shell comands to ~/.vnc/xstartup

#!/bin/sh
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
/usr/bin/startxfce4
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
x-window-manager &

Using unset SESSION_MANAGER prevents conflicts with other session managers when starting a desktop in a VNC session. Similarly, unset DBUS_SESSION_BUS_ADDRESS initiates a fresh D-Bus session for VNC, avoiding communication issues. /usr/bin/startxfce4 then starts the XFCE desktop environment as the main interface for VNC connections.

[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup: Executes the script if /etc/vnc/xstartup is present and executable, allowing for session initialization. If executed after startxfce4, it indicates startxfce4 failed or ran in the background.

[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources If the .Xresources file is readable, it loads X resources (e.g., terminal colors and fonts) to customize X applications in the VNC session.

x-window-manager & starts the window manager, which controls window placement, appearance, and behavior in an X session. This command is typically a symbolic link to the default system window manager such as openbox, twm, ctwm, or mwm.

Now you can start the server:

$ vncserver :1

Connect to the remote desktop using a VNC client, such as tightVNC for Windows. Enter the server’s Public IP in the client’s Host Name field to access the XFCE desktop environment remotely.

VNC connections are not encrypted by default. Use an SSH tunnel via PuTTY to secure them. Open PuTTY and enter user@IP-Address as the host name. In Connections, under SSH > Tunnels, set 5901 as source port and IP-Address:5901 as destination, select Local and Auto. Click Add, save the session, and open the connection. Log in with your credentials. To access the XFCE session, use a VNC client like tightVNC and connect to localhost:1.

Troubleshooting

Start the vncserver, and run sudo netstat -plutn. If it shows 127.0.0.1:1 or ::1, it’s running on localhost and inaccessible from outside. Ensure ~/.vnc/config includes localhost=no. To check if the port is open on Windows, use netstat -ano | grep 5901, yielding output like:

TCP 127.0.0.1:5901 0.0.0.0:0 LISTENING 7856
TCP [::1]:5901 [::]:0 LISTENING 7856

References

Rout S., “Understanding and using the X Window System”, SRBlog 2024. Link.