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Remote access to a Linux host's desktop with VNC

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 in combination with your eth_network_password.
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 your Linux 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 your Linux host

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

Initiate a SSH connection to your Linux host

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. 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.

Kill 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.

Startup after previous setup

View and control the desktop on your Linux host

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 own on your home computer.

TigerVNC viewer is installed on managed Linux clients
On managed Windows clients, RealVNC viewer is installed on request

Check (student) host availability

Check with the command htop if any other users are using C'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

And Mac users?

To be documented. Hint: Everything you need is already available in macOS.

VNC on Wikipedia (1)

-  ⇤ ← Revision 1 as of 2020-03-22 19:47:51 → 
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+   ← Revision 4 as of 2020-03-22 22:10:32 → ⇥
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-Deletions are marked like this.
+Additions are marked like this.
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-The following article explains how to access the desktop of a Linux host residing inside the ETH network from another host on the in- and outside. Throughout the article, the following placeholders are used:
 * Host '''A'''<<BR>>
 This is a remote host in- or outside the ETH network, i.e. your home computer. It will run the software to view a desktop, the [[#VNC_viewer_software|VNC viewer]].
 * Host '''B'''<<BR>>
 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. It is not necessary when you're using VPN.
 * Host '''C'''<<BR>>
 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_.28student.29_host_availability|check it's availability]] at login.
+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 __V__irtual __N__etwork __C__omputing (VNC)<<FootNote([[https://en.wikipedia.org/wiki/Virtual_Network_Computing|VNC on Wikipedia]])>>. 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_software|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_.28student.29_host_availability|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''.
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-== How to access a host with VNC ==
Activate your VPN connection to ETH if your host '''A''' resides outside of the ETH network. The eduroam WLAN is outside the ETH network.
Initiate a SSH connection to host '''C'''
Start a VNC server on host '''C'''
Connect from host '''A''' to host '''C'''
+== 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.<<BR>>
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 [[https://password.ethz.ch/|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 [[https://sslvpn.ethz.ch/|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'' in combination with your ''eth_network_password''.
 * If you have access to additional realms, a.k.a virtual private Zones (VPZ), you can list them by visiting [[https://realms.ethz.ch/|realms.ethz.ch]].

=== Initiate a VPN connection to your Linux 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 your Linux host ==
To start a VNC server instance on ''internal_host'', you need to initiate a SSH connection to it.

=== Initiate a SSH connection to your Linux host ===
 * 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 [[https://www.chiark.greenend.org.uk/~sgtatham/putty/|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. 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.<<BR>>
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.<<BR>>
Otherwise the vncserver process terminates after you log out of your desktop environment.

==== Kill 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.

==== Startup after previous setup ====


== View and control the desktop on your Linux host ==

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