X11vnc

From Leo's Notes
Last edited on 25 January 2023, at 00:29.

x11vnc is a VNC server which mirrors the current on the X11 display rather than creating a separate X11 display such as Xvnc. This is useful for remote control purposes. It may also be used as a remote desktop solution, but keep in mind that x11vnc will only display the desktop and does not support audio.

Usage

x11vnc can be started by just running the x11vnc binary. There are a few additional files that you should be aware of:

  • $HOME/.vnc/passwd should contain your VNC password generated using x11vnc -storepasswd and enabled with the -rfbauth $filename option.
  • ~/.x11vncrc is the x11vnc rc file which contains should contain all available options as well its default values.
  • ~/.x11vnc.log.* should be the log file for your VNC session (can be changed with the -logfile option)

Configuration

You can configure x11vnc by editing the ~/.x11vncrc file. Here's my configuration: 

-bg				# default: off
-defer 10			# default:  20
-forever			# default: off
-logfile /home/leo/.x11vnc.log.hostname:5900	# default:  ""
-ncache				# default: on
-repeat
-overlay_nocursor		# default: off
-nevershared
-wait 10			# default:  20
-noxdamage
-xkb				# default: off
-shared

The options in the RC file can be overridden by passing its option to x11vnc when invoking the command. For example, I can run x11vnc -rfbauth $HOME/.vnc/passwd to override whatever value was defined in the .x11vncrc file.

Starting x11vnc

The most basic usage is to just run x11vnc on a console. The VNC port number will be printed after it has started.

Starting with systemd

To run x11vnc for a specific user when they log in, create the following systemd service file:

$HOME/.config/systemd/user/x11vnc.service 

[Unit]
Description=start x11vnc

[Service]
ExecStart=/usr/bin/x11vnc -noncache -forever -loop -noxdamage -repeat -rfbauth /home/leo/.vncpasswd

[Install]
WantedBy=default.target

Enable and start the service as a user with: 

$ systemctl --user enable x11vnc.service
$ systemctl --user start x11vnc.service
$ systemctl --user status x11vnc.service

Troubleshooting

Multiple connections are not working

When using X11vnc with Guacamole, multiple connections to the same VNC session isn't working. Subsequent connections render a "The remote desktop server is currently unavailable. If the problem persists, please notify your system administrator" error message even though the VNC connection on Guacamole's configuration allow sfor multiple connections.

According to the VNC logs, the second connection is getting refused:

24/01/2023 17:11:10 rfbProcessClientSecurityType: executing handler for type 2
24/01/2023 17:11:10 -dontdisconnect: Not shared & existing client
24/01/2023 17:11:10   refusing new client 10.1.2.11

To fix this, edit the .x11vncrc file and add a -shared option.