Difference between revisions of "VNC"

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Other VNC viewers will also work, such as [https://www.tightvnc.com/download.php TightVNC] and RealVNC
 
Other VNC viewers will also work, such as [https://www.tightvnc.com/download.php TightVNC] and RealVNC
  
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=== Mac or Linux ===
 
  
 
The instructions given when you started the session on <code>portal1</code> are OK but it always tells you to start a session (in a terminal on your mac or linux machine command line)
 
The instructions given when you started the session on <code>portal1</code> are OK but it always tells you to start a session (in a terminal on your mac or linux machine command line)
  
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  ssh -L5905:portal1:59zw jumpgate-phasta.colorado.edu
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  ssh -L59zw:portal1:59zw jumpgate-phasta.colorado.edu
  
 
where <code>zw</code> will be different for each user. That suggestion is OK if you never plan to connect to anyone else's session but since we often collaborate but sharing VNC sessions, the better practice we adopt is to use <code>zw</code> in place of the suggested 05 (which just an arbitrary local port on your laptop). So if when I created a session the last for numbers were <code>5923</code> then <code>zw</code> for me is <code>23</code> and the best practice is to ignore the script suggestion in favor of
 
where <code>zw</code> will be different for each user. That suggestion is OK if you never plan to connect to anyone else's session but since we often collaborate but sharing VNC sessions, the better practice we adopt is to use <code>zw</code> in place of the suggested 05 (which just an arbitrary local port on your laptop). So if when I created a session the last for numbers were <code>5923</code> then <code>zw</code> for me is <code>23</code> and the best practice is to ignore the script suggestion in favor of
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  ssh -L5923:portal1:5923 jumpgate-phasta.colorado.edu
 
  ssh -L5923:portal1:5923 jumpgate-phasta.colorado.edu
  
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=== Windows ===
 
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The PuTTY SSH client can handle ssh tunneling on Windows based machines. You can download it [http://www.chiark.greenend.org.uk/~sgtatham/putty/ here].
 
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When you open putty, enter <code>jumpgate-phasta.colorado.edu</code> in the "Host Name" box. Then click the + button next to SSH on the left pane (to expand the SSH tree node). Choose the "Tunnels" page. The <code>start_vnc.sh</code> script should tell you to run <code>ssh -L59xy:portal1:59zw jumpgate-phasta.colorado.edu</code> on your machine. Those instructions are OK but a better practice is to ignore what that script suggested for <code>xy</code> (it always suggests 05 currently) and instead use <code>ssh -L59zw:portal1:59zw jumpgate-phasta.colorado.edu" where <code>zw</code> varies for each new session created.  If you get <code>23</code> that just means there were <code>22</code> sessions created before you created this one (but the plan is for you to keep using 23 until the machine gets rebooted). Enter <code>59zw</code> in the "Source Port" box. Enter <code>portal1:59zw</code> in the "Destination" box (starting and ''click the add button''). Putty is a little strange about saving the session which you want to do to avoid having to do all the above every time you re-connect. ''BEFORE'' you click the "Open" button, you want to name your session (your choice) and click save.  Then in the future when you start putty you should be able to just click that saved session name and click load. Then click "Open" and login as normal. You will then be able to use a vncviewer as instructed by the script.
 
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Example:
 
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The script says:
 
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<code>ssh -L5905:portal1:5923 jumpgate-phasta.colorado.edu</code>
 
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your <code>zw</code> from the instructions above is <code>23</code>
 
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enter <code>5923</code> in the "Source Port" box
 
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enter <code>portal1:5923</code> in the destination box.
 
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====Connecting to your VNC with PuTTY====
 
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Once we SSH to jumpgate (on the default SSH port 22), our main desktop on portal1 can be accessed via a VNC session as follows.
 
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# The VNC server should already be running on portal1 using port 59zw.
 
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#* To check the port, on portal1 run <code>/opt/vnc_script/findsession.sh</code>
 
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#* To confirm the VNC server is running (and see port), run <code>ps aux | grep vnc</code>
 
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# Open PuTTY on your local machine.
 
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# Under "Session", SSH to <code>USERNAME@jumpgate-phasta.colorado.edu:22</code>, where <code>USERNAME</code> is your username on <code>jumpgate</code>, and <code>22</code> is the standard SSH port.
 
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# Under "Session">"SSH">"Tunnels", select source port <code>59##</code> and destination port <code>portal1:59##</code>, where <code>##</code> is the two-digit number of your VNC session. Select destination <code>local</code> and click "Add".
 
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#* We select <code>local</code> because we have a service (VNC Server) running on a machine (<code>portal1</code>) that can be reached from the remote machine (<code>jumpgate</code>), and we want to access it directly from the <code>local</code> machine.
 
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# Confirm the dialog by clicking "Open", thus establishing an SSH connection between <code>localhost</code> and <code>jumpgate</code>, and tunneling <code>localhost:59##</code> to <code>portal1:59##</code> via this connection.
 
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# Open RealVNC, and connect to <code>localhost:##</code>, which is shorthand for <code>localhost:59##</code>. VNC ports are enumerated starting with <code>5901</code>, so any two digit port <code>##</code> is assumed to be port <code>59##</code>.
 
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# You should now have access to your desktop on <code>portal1</code>. DON'T FORGET-- no meshing, solving, post-processing, EVEN MATLAB on <code>portal1</code>. To run memory and/or processor and/or graphics intensive jobs you need to create a terminal and type <code>vglconnect -s viz00x</code>  where, at this time <code>x</code> is either 2 or 3.
 
  
 
=== Starting a VNC viewer ===
 
=== Starting a VNC viewer ===

Revision as of 14:20, 9 September 2020

Virtual Network Computing (VNC) is a tool which projects a GUI session over the network. If may be useful if you want to use GUI tools remotely when X forwarding performs poorly.

VNC works on a client-server architecture, where a remote system (server) runs the programs and sends the virtual screen output to the local system (client). Here, the local system would be your laptop/desktop, while the server is located on the PHASTA Group Machines.

VNC on PHASTA Machines

Warning: The VNC password is transmitted in clear text over the network and should not be considered secure

Server-Side Setup for PHASTA Machines

Start VNC Server

portal1 is designated to host VNC sessions.

To start a VNC session type the following with a return after each line: 

 ssh jumpgate-phasta.colorado.edu
 ssh portal1
 source /etc/profile
 start_vnc.sh

Then follow the directions from start_vnc.sh. Make sure to remember your password and port number (59**) so that you can reuse your session.

It is common practice to leave your VNC session running on portal1. Next time you want to access your desktop, just ssh into jumpgate with a tunnel between portal1's VNC port (59**) and some port on your machine. Then use a VNC client to connect to the port on your machine.

Kill VNC Server

If, for some reason, you want to end your session and kill your virtual desktop, run 

 source /etc/profile
 stop_vnc.sh    # ONLY run this if you want to kill your virtual desktop. Most users will never need to do this as the idea is to create one session and continue to use that one for all future usage.

Changing the VNC Password

On portal1: 

 /opt/tigervnc/bin/vncpasswd

View Only Mode

To share your desktop with another user in view only mode set a view only password by running 

 vncpasswd

Have the other user connect in the same way you would but have them set their viewer to be in view only mode and use your view only password. Typically this is done as follows: 

 vncviewer -viewonly

Changing the Size (Resolution) of an Existing Session

Note: In most modern VNC clients, this can (possibly should) be done via the locally running client. See your VNC client's documentation for details. The below is kept for posterity

You can usually use the xrandr tool to change the resolution of a running VNC session. First you'll need to know your session's display number (this should be the last digit or two of the port number). For example, if your VNC session is running on port 5902, then your screen number should be :2. For this example, we'll use screen 2.

Once you know your screen number, you can see the list of supported modes as follows: 

 xrandr -display :2

Once you pick the one you want (generally the same size or smaller than the native resolution of your client), you can choose it by running a command like 

 xrandr -s 1400x1050 -display :2

(this example will set the resolution to 1400 pixels by 1050 pixels)

You'll probably be disconnected at this point, but when you reconnect your screen size should be changed (hopefully without crashing your running programs).

Finding an Existing Session

SSH to portal1 and then run: 

 /opt/vnc_script/findsession.sh

Which will return the shortened port number of each of your currently running sessions.

Client-Side Setup for PHASTA Machines

Clients

portal1 uses TurboVNC from the VirtualGL project, available from their website

Other VNC viewers will also work, such as TightVNC and RealVNC


The instructions given when you started the session on portal1 are OK but it always tells you to start a session (in a terminal on your mac or linux machine command line) 

ssh -L59zw:portal1:59zw jumpgate-phasta.colorado.edu

where zw will be different for each user. That suggestion is OK if you never plan to connect to anyone else's session but since we often collaborate but sharing VNC sessions, the better practice we adopt is to use zw in place of the suggested 05 (which just an arbitrary local port on your laptop). So if when I created a session the last for numbers were 5923 then zw for me is 23 and the best practice is to ignore the script suggestion in favor of 

ssh -L5923:portal1:5923 jumpgate-phasta.colorado.edu


Starting a VNC viewer

Whether you followed the Mac or Linux or Windows instructions above, successful completion will have established a tunnel from your laptop to portal1. The last step is to start a VNC viewer (graphical windowing program) that uses this tunnel to display your portal1 session on the screen of your laptop. There are a variety of choices for each platform and they evolve but their operation seems, thankfully, pretty universal.

The most basic input is that they provide a box that says VNC server. You will want to type localhost:zw in that box and then apply start (or whatever the particular applications action button is). The zw here will need to be whatever you used after the 59zw:portal1..... part of the tunnel. What the number is actually doing is telling this VNC viewer which port you have established a tunnel on for the session you are starting the VNC viewer for. Note it is possible to have several different simultaneous sessions. Each needs its own tunnel (established by repeating the process above with a unique zw) and then a corresponding "new" VNC viewer. In this way we might continue to work in our own session but then take a break to look at a collaborator's session without having to close out the tunnel and viewer pair.

Web Based Viewer

If you can't or don't want to install a VNC viewer you can use a Java based one. You will need a JVM and a Java browser plugin. You will also need the port that the start_vnc script assigned you to be free on your local computer

Forward your session through jumpgate as before before, adding a second port, 580n. For example, if the script tells you to

ssh -L5905:portal1:5902 jumpgate-phasta.colorado.edu you should 

 ssh -L5902:portal1:5902 -L5802:portal1:5802 jumpgate-phasta.colorado.edu

Then point your browser to http://localhost:5802 and log in with the password specified by the script when prompted. (Replace 2 with the value specified by the script)

OpenGL

portal1 is equipped with a VirtualGL install which will allow you to use OpenGL programs (which do not use pthreads)

Simply wrap your OpenGL program with the vglrun command 

 vlgrun glxgears

Our lab has 2 VirtualGL servers you can connect to from portal1. You must connect to one of them for large memory and/or computationally intensive processes. The names of the servers are viz002 and viz003 (viz001 is probably never coming back to life). portal1 doesn't have a particularly fast graphics processor and MUST NOT be used for large memory or computationally intensive process) 

 vglconnect -s viz002

or 

 vglconnect -s viz003

from this connection you will want to run graphic applications (e.g., SimModeler or ParaView) prefaced by the command vglrun. You can test that you have it setup right with the toy-app glxgears as follows 

 vglrun glxgears

Note that VGL uses a number of threads. If you have trouble with vglrun crashing with a message about Thread::Start() make sure you haven't set your stack size too large (remove any ulimit -s or ulimit -n calls from your shell start scripts).

NOTE ALSO: The primary purpose for viz003 is for visualization and for debugging. Production runs should be done elsewhere.

Troubleshooting

If you have used vncserver (It doesn't matter which version) before, you will need to clear your vnc settings for the script to work. You can do this by running rm -rf ~/.vnc

stop_vnc.sh may display some errors; this is normal.

If you have trouble deleting ~/.vnc send an email to Benjamin.A.Matthews@colorado.edu

If any of these commands fail, you may need to source /etc/profile to get the necessary environment variables (this should be fixed soon)

VirtualGL has trouble with some threaded programs. If your OpenGL program exhibits segmentation faults or other issues, this could be the problem. Check back for the solution later.

If the given password is rejected you can run stop_vnc.sh and restart to get a new one. Occasionally the random password generator may generate passwords which VNC doesn't like.

If VirtualGL complains about not being able to get a 24bit FB config either vglconnect to another VirtualGL enabled server or complain to Benjamin.A.Matthews@Colorado.edu

If your VNC connection is very slow, you might want to try changing the compression and encoding options. See your vncviewer's documentation or try this 

 vncviewer -encodings tight -quality 6 -compresslevel 6

If you have trouble with text distortion try adding 

 -nojpeg

If you're running OSX and see an error about Zlib, try changing your compression settings (maximum quality usually works) or use a different client. RealVNC and certain versions of ChickenOfTheVNC both exhibit this issue. The latest build of TigerVNC should work reliably, as does the Java based TightVNC client.

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