# VNC
The **Virtual Network Computing** (**VNC**) is a graphical [desktop sharing](http://en.wikipedia.org/wiki/Desktop_sharing "Desktop sharing") system that uses the [Remote Frame Buffer protocol (RFB)](http://en.wikipedia.org/wiki/RFB_protocol "RFB protocol") to remotely control another [computer](http://en.wikipedia.org/wiki/Computer "Computer"). It transmits the [keyboard](http://en.wikipedia.org/wiki/Computer_keyboard "Computer keyboard") and [mouse](http://en.wikipedia.org/wiki/Computer_mouse") events from one computer to another, relaying the graphical [screen](http://en.wikipedia.org/wiki/Computer_screen "Computer screen") updates back in the other direction, over a [network](http://en.wikipedia.org/wiki/Computer_network "Computer network").
Vnc-based connections are faster (require less network bandwidth) then [X11](x-window-system) applications forwarded directly through ssh.
The recommended clients are [TightVNC](http://www.tightvnc.com) or [TigerVNC](http://sourceforge.net/apps/mediawiki/tigervnc/index.php?title=Main_Page) (free, open source, available for almost any platform).
## Create VNC Password
!!! note
Local VNC password should be set before the first login. Do use a strong password.
```console
[username@login2 ~]$ vncpasswd
Password:
Verify:
```
## Start Vncserver
!!! note
To access VNC a local vncserver must be started first and also a tunnel using SSH port forwarding must be established.
[See below](vnc.md#linux-example-of-creating-a-tunnel) for the details on SSH tunnels. In this example we use port 61.
You can find ports which are already occupied. Here you can see that ports " /usr/bin/Xvnc :79" and " /usr/bin/Xvnc :60" are occupied.
```console
[username@login2 ~]$ ps aux | grep Xvnc
username 5971 0.0 0.0 201072 92564 ? SN Sep22 4:19 /usr/bin/Xvnc :79 -desktop login2:79 (username) -auth /home/vop999/.Xauthority -geometry 1024x768 -rfbwait 30000 -rfbauth /home/username/.vnc/passwd -rfbport 5979 -fp catalogue:/etc/X11/fontpath.d -pn
username 10296 0.0 0.0 131772 21076 pts/29 SN 13:01 0:01 /usr/bin/Xvnc :60 -desktop login2:61 (username) -auth /home/vop999/.Xauthority -geometry 1600x900 -depth 16 -rfbwait 30000 -rfbauth /home/vop999/.vnc/passwd -rfbport 5960 -fp catalogue:/etc/X11/fontpath.d -pn
.....
```
Choose free port e.g. 61 and start your VNC server:
```console
[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 if VNC server is started on the port (in this example 61):
```console
[username@login2 .vnc]$ vncserver -list
TigerVNC server sessions:
X DISPLAY # PROCESS ID
:61 18437
```
Another command:
```console
[username@login2 .vnc]$ ps aux | grep Xvnc
username 10296 0.0 0.0 131772 21076 pts/29 SN 13:01 0:01 /usr/bin/Xvnc :61 -desktop login2:61 (username) -auth /home/vop999/.Xauthority -geometry 1600x900 -depth 16 -rfbwait 30000 -rfbauth /home/username/.vnc/passwd -rfbport 5961 -fp catalogue:/etc/X11/fontpath.d -pn
```
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 this case).
!!! note
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:
```console
local $ ssh -TN -f username@login2.cluster-name.it4i.cz -L 5961:localhost:5961
```
Issue the following command to check the tunnel is established (please note the PID 2022 in the last column, you'll need it for closing the tunnel):
```console
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:
```console
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:
```console
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):
```console
kill 2022
```
## Windows Example of Creating a Tunnel
Use PuTTY to log in on cluster.
Start vncserver using command vncserver described above.
Search for the localhost and port number (in this case 127.0.0.1:5961).
```console
[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**.
Run the VNC client of your choice, select VNC server 127.0.0.1, port 5961 and connect using VNC password.
## Example of Starting TigerVNC Viewer
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.
## Example of Starting TightVNC Viewer
Use your VNC password to log using TightVNC Viewer and start a Gnome Session on the login node.
## Gnome Session
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.
```console
[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:
```console
[username@login2 .vnc]$ vncserver -kill :61
Killing Xvnc process ID 7074
Xvnc process ID 7074 already killed
```
Or this way:
```console
[username@login2 .vnc]$ pkill vnc
```
## 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:
```console
$ xhost +
```
Get an interactive session on a compute node (for more detailed info [look here](../../../anselm/job-submission-and-execution/)). Use the **-v DISPLAY** option to propagate the DISPLAY on the compute node. In this example, we want a complete node (24 cores in this example) from the production queue:
```console
$ qsub -I -v DISPLAY=$(uname -n):$(echo $DISPLAY | cut -d ':' -f 2) -A PROJECT_ID -q qprod -l select=1:ncpus=24
```
Test that the DISPLAY redirection into your VNC session works, by running a X11 application (e. g. XTerm) on the assigned compute node:
```console
$ xterm
```
Example described above:
