The Virtual Network Computing (VNC) is a graphical desktop sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer). It transmits the keyboard and mouse events from one computer to another, relaying the graphical screen updates back in the other direction, over a network.
Vnc-based connections are usually faster (require less network bandwidth) then X11 applications forwarded directly through ssh.
In this chapter we show how to create an underlying ssh tunnel from your client machine to one of our login nodes. Then, how to start your own vnc server on our login node and finally how to connect to your vnc server via the encrypted ssh tunnel.
Create VNC Password¶
Local VNC password should be set before the first login. Do use a strong password.
[username@login2 ~]$ vncpasswd Password: Verify:
To access VNC a local vncserver must be started first and also a tunnel using SSH port forwarding must be established.
See below for the details on SSH tunnels.
You should start by choosing your display number. To choose free one, you should check currently occupied display numbers - list them using command:
[username@login2 ~]$ ps aux | grep Xvnc | sed -rn 's/(\s) .*Xvnc (\:[0-9]+) .*/\1 \2/p' username :79 username :60 .....
As you can see above, displays ":79" and ":60" we had occupied already. Generally, you can choose display number freely except these occupied numbers. Also remember that display number should be less or equal 99. Based on this we have choosen display number 61 for us, so this number you can see in examples below.
Your situation may be different so also choose of your number may be different. Please choose and use your own display number accordingly!
Start your VNC server on choosen display number (61):
[username@login2 ~]$ vncserver :61 -geometry 1600x900 -depth 16 New 'login2:1 (username)' desktop is login2:1 Starting applications specified in /home/username/.vnc/xstartup Log file is /home/username/.vnc/login2:1.log
Check whether VNC server is running on choosen display number (61):
[username@login2 .vnc]$ vncserver -list TigerVNC server sessions: X DISPLAY # PROCESS ID :61 18437
Another way to check it:
[username@login2 .vnc]$ ps aux | grep Xvnc | sed -rn 's/(\s) .*Xvnc (\:[0-9]+) .*/\1 \2/p' username :61 username :102
The VNC server runs on port 59xx, where xx is the display number. So, you get your port number simply as 5900 + display number, in our example 5900 + 61 = 5961. Another example for display number 102 is calculation of TCP port 5900 + 102 = 6002 but be aware, that TCP ports above 6000 are often used by X11. Please, calculate your own port number and use it instead of 5961 from examples below!
To access the VNC server you have to create a tunnel between the login node using TCP port 5961 and your machine using a free TCP port (for simplicity the very same) in next step. See examples for Linux/Mac OS and Windows.
The tunnel must point to the same login node where you launched the VNC server, eg. login2. If you use just cluster-name.it4i.cz, the tunnel might point to a different node due to DNS round robin.
Linux/Mac OS Example of Creating a Tunnel¶
At your machine, create the tunnel:
local $ ssh -TN -f email@example.com -L 5961:localhost:5961
Issue the following command to check the tunnel is established (note the PID 2022 in the last column, you'll need it for closing the tunnel):
local $ netstat -natp | grep 5961 (Not all processes could be identified, non-owned process info will not be shown, you would have to be root to see it all.) tcp 0 0 127.0.0.1:5961 0.0.0.0:* LISTEN 2022/ssh tcp6 0 0 ::1:5961 :::* LISTEN 2022/ssh
Or on Mac OS use this command:
local-mac $ lsof -n -i4TCP:5961 | grep LISTEN ssh 75890 sta545 7u IPv4 0xfb062b5c15a56a3b 0t0 TCP 127.0.0.1:5961 (LISTEN)
Connect with the VNC client:
local $ vncviewer 127.0.0.1:5961
In this example, we connect to VNC server on port 5961, via the ssh tunnel. The connection is encrypted and secured. The VNC server listening on port 5961 provides screen of 1600x900 pixels.
You have to destroy the SSH tunnel which is still running at the background after you finish the work. Use the following command (PID 2022 in this case, see the netstat command above):
Windows Example of Creating a Tunnel¶
Start vncserver using command vncserver described above.
Search for the localhost and port number (in this case 127.0.0.1:5961).
[username@login2 .vnc]$ netstat -tanp | grep Xvnc (Not all processes could be identified, non-owned process info will not be shown, you would have to be root to see it all.) tcp 0 0 127.0.0.1:5961 0.0.0.0:* LISTEN 24031/Xvnc
On the PuTTY Configuration screen go to Connection->SSH->Tunnels to set up the tunnel.
Fill the Source port and Destination fields. Do not forget to click the Add button.
WSL (Bash on Windows)¶
Windows Subsystem for Linux is another way to run Linux software in a Windows environment.
At your machine, create the tunnel:
local $ ssh firstname.lastname@example.org -L 5961:localhost:5961
Example of Starting VNC Client¶
Run the VNC client of your choice, select VNC server 127.0.0.1, port 5961 and connect using VNC password.
In this example, we connect to VNC server on port 5961, via the ssh tunnel, using TigerVNC viewer. The connection is encrypted and secured. The VNC server listening on port 5961 provides screen of 1600x900 pixels.
Use your VNC password to log using TightVNC Viewer and start a Gnome Session on the login node.
You should see after the successful login.
Disable Your Gnome Session Screensaver¶
Open Screensaver preferences dialog:
Uncheck both options below the slider:
Kill Screensaver if Locked Screen¶
If the screen gets locked you have to kill the screensaver. Do not to forget to disable the screensaver then.
[username@login2 .vnc]$ ps aux | grep screen username 1503 0.0 0.0 103244 892 pts/4 S+ 14:37 0:00 grep screen username 24316 0.0 0.0 270564 3528 ? Ss 14:12 0:00 gnome-screensaver [username@login2 .vnc]$ kill 24316
Kill Vncserver After Finished Work¶
You should kill your VNC server using command:
[username@login2 .vnc]$ vncserver -kill :61 Killing Xvnc process ID 7074 Xvnc process ID 7074 already killed
Or this way:
[username@login2 .vnc]$ pkill vnc
Do not forget to terminate also SSH tunnel, if it was used. Look on end of this section for the details.
GUI Applications on Compute Nodes Over VNC¶
The very same methods as described above, may be used to run the GUI applications on compute nodes. However, for maximum performance, proceed following these steps:
Open a Terminal (Applications -> System Tools -> Terminal). Run all the next commands in the terminal.
Allow incoming X11 graphics from the compute nodes at the login node:
$ xhost +
Get an interactive session on a compute node (for more detailed info look here). Use the -v DISPLAY option to propagate the DISPLAY on the compute node. In this example, we want a complete node (16 cores in this example) from the production queue:
$ qsub -I -v DISPLAY=$(uname -n):$(echo $DISPLAY | cut -d ':' -f 2) -A PROJECT_ID -q qprod -l select=1:ncpus=16
Test that the DISPLAY redirection into your VNC session works, by running a X11 application (e. g. XTerm) on the assigned compute node:
Example described above: