Remote access to a Linux host's desktop with VNC

The following article explains how to access the desktop of a Linux host residing inside the ETH network from another host on the in- or outside by using Virtual Network Computing (VNC)¹. Throughout his article, the following placeholders are used:

• current_host: This is a remote host in- or outside the ETH network, i.e. your office computer or home computer; the host you are currently working on. It will run the software to view a remote Linux desktop, the VNC viewer.

• gateway_host: This is the entrance gateway to the ETH network to bypass the firewall restrictions for connections from the outside, by the name of login.ee.ethz.ch. It is used to tunnel SSH connections in case you choose not to use VPN.

• internal_host: This is the target host you intend to connect to. If it's your personal PC in your office you know its name. Students can use an arbitrary shared student room PC like tardis-d12. If you're using a shared student PC, check it's availability at login.

• eth_username: This is the username you use to log in anywhere on an ETH provided IT service.

• eth_password: This is your password used in combination with your eth_username which lets you access ETH provided IT services, except for network authentications (see below).

• eth_network_password: This is your password also used in combination with your eth_username which is used for authentication to network services like Wifi and VPN. It is different from your eth_password.

Connect to the ETH network

If current_host resides outside of the ETH network, you need to connect to it by initiating a VPN connection. The following steps explain the necessary prerequisites.
If current_host is alreay inside the ETH network, skip to the next paragraph.

Know your ETH network password

If you're unsure about your eth_network_password, login on password.ethz.ch with your regular eth_password and change your former eth_network_password to a new password.

Install the VPN client on your current host

• Go to sslvpn.ethz.ch and follow the instructions provided there to download, install and configure the Cisco AnyConnect VPN client provided by central IT services.

• To log in here you have to use your eth_username with an added realm in combination with your eth_network_password, as described on sslvpn.ethz.ch.

• If you have access to additional realms, a.k.a virtual private Zones (VPZ), you can list them by visiting realms.ethz.ch.

Initiate a VPN connection to internal_host

• Now you are ready to connect the VPN client on current_host to the ETH network and continue with the following steps.

Start a VNC server on internal_host

To start a VNC server instance on internal_host, you need to initiate a SSH connection to it.

Initiate a SSH connection to internal_host

• Make sure your VPN connection to the ETH network is active

• If current_host is a Linux client, issue the command

  ssh eth_username@internal_host

  in your terminal and log in with your eth_password.

• If current_host is a Windows 10 client you can use the optional installable feature (Apps -> Optional features -> OpenSSH Client) to issue the command as described for a Linux client above.

• Alternatively, you can follow the article about WindowsDirectSSHAccess for a comfortable setup with putty on Windows.

Setup and start the VNC server

Configuration and start of a VNC server works with an ISG-provided wrapper script by issuing the command

vncserver

in your shell connected to internal_host.

Setup and first startup

If this is the first time you start vncserver, you will be asked to provide a password to allow access to the VNC server instance you start now and in the future. It is possible to set the password to allow only observing or also interacting with the VNC session. Seelct a strong password, as anyone on the ETH network can connect to your internal_host while a VNC server is running. The password should contain:

• 8 characters²

• Uppercase letters
• Lowercase letters
• Numbers

The standard VNC implementation uses the password as a DES key, which is the reason it's truncated after 8 characters.
The setup followed by the startup process will look like this:

Creating directory /home/eth_username/.vnc......
Creating startup_file /home/eth_username/.vnc/xstartup.....

You will require a password to access your desktops.

Password:
Verify:
Would you like to enter a view-only password (y/n)? n

New 'default' desktop is internal_host:N

Creating default config /home/eth_username/.vnc/config
Starting applications specified in /home/eth_username/.vnc/xstartup
Log file is /home/eth_username/.vnc/internal_host:N.log

Note the virtual display number N of your VNC server appearing after internal_host:. It is needed later to connect your VNC viewer on current_host to the VNC server instance on internal_host or to kill a vncserver process manually.
The default desktop started now is Xfce4. If you prefer a different desktop you have to kill the running vncserver process and start it again with the desktop of your choice.
Otherwise the vncserver process terminates after you log out of your desktop environment.

Terminating a running VNC server process

Issue the command

vncserver -kill :N

in a shell on internal_host.

Choose a non-default desktop

To start the VNC session with a non-default desktop, provide one of the options [xfce|gnome|kde|light|xterm]:

vncserver gnome

• Option light starts the light desktop Fluxbox

• Option xterm starts a minimal desktop with a window manager and a xterm terminal window. This option should be used if you intend to use your session to run only one application at the time and start said application on the command line.

Use a VNC viewer to view and control the desktop on internal_host

• If your current_host is an ISG-managed Linux computer a VNC viewer is installed.

• If it is a ISG-managed Windows computer you have to request installation of a VNC viewer.
• If you use your self-managed office or your personal home computer you have to install a viewer yourself.

VNC viewer software

The listed VNC software contains a viewer component and is available for both Linux and Windows:

• TightVNC: Opensource

• TigerVNC: Opensource, a fork of TightVNC with additional features

• TurboVNC: Opensource, a fork of TightVNC with peak 3D/video performance as a goal

• RealVNC: Freeware

The above list is not meant to be complete, feel free to install other solutions on your self-managed computer.

• TigerVNC viewer is installed on managed Linux clients
• On managed Windows clients, RealVNC viewer is installed on request.
• On private Windows clients, use of RealVNC is discouraged. Some versions show error messages similar to "RFB protocol error bad rectangle size 10794x10794" and fail to connect.

Connect your VNC viewer to the VNC server on internal_host

On a Linux client

On a Linux client issue the command

vncviewer internal_host:N

On a Windows or Mac client

On a Windows or Mac client enter the hostname of internal_host and the display number N as shown in the following example for TurboVNC viewer:

If you terminate your VNC viewer without logging out of your desktop environment, your VNC session will stay active and you can reconnect to it later on.

Mac client alternative

On a Mac client the built-in VNC viewer may be started by pressing Command-K and entering the url vnc://internal_host:590N. No support is given for this way to connect to a VNC session.

Misc

Check (student) host availability

Check with the command htop if any other users are using internal_host 's resources right now. If they do, log out and log in to a different host.
A list of student hosts can be shown by issuing the command grep tardis /etc/hosts

Advanced usage

Some advanced configuration or usage examples have not yet been migrated from the previous documentation about VNC.

Virtual display size

The size of the virtual display can be set by entering its dimensions in pixel in either /home/eth_username/.vnc/config.turbo for gnome sessions or /home/eth_username/.vnc/config for all other sessions by adding a line similar to the following:

geometry=3840x1200