VNC: Difference between revisions

First you will need to install a VNC client on your machine to connect to the VNC server.  We recommend using [http://tigervnc.org/ TigerVNC].  A TigerVNC package is available for Windows, MacOS and most Linux distributions.  The following shows how to download, install and configure TigerVNC securely for each operating system.  The certificate configuration steps are only required for connecting to VDI Nodes so the signing authority of the certificate presented by the vncserver is known. If a popup about a certificate issue occurs either you have not configured it properly or you are not connected to our server and should not enter your password.

Download and run the latest [https://bintray.com/tigervnc/stable/tigervnc/ tigervnc64-x.y.z.exe] installer.  Be sure to uncheck both "Register new TigerVNC Server as a system service and "Start or restart TigerVNC service" - these options are for sharing your desktop and not for connecting to our systems.  Next, click to download [https://curl.haxx.se/ca/cacert.pem cacert.pem] to a local directory.  Configure the default viewer settings by clicking the desktop TigerVNC Viewer icon.  In the "VNC Viewer: Connection Details" window that appears click "Options -> Security" then tick all boxes except Encryption None and enter your  <code>C:\full\directory\pathto\cacert.pem</code> in the "Path to X509 CA Certificate" field.  To save the settings click OK and then click Connect (if Connect is not clicked the settings will not be saved).  Lastly, to create secure tunnels from your desktop to the vncserver as described in the below sections, you will need to open a terminal window and run the ssh command.  This maybe done using PowerShell standard on Windows 10 since the 1809 October Update.

Download and run the latest [https://bintray.com/tigervnc/stable/tigervnc/ tigerVNC-x.y.z.dmg] package installer.  Configure the default viewer settings by clicking the desktop TigerVNC Viewer icon. In the "VNC Viewer: Connection Details" window that appears click "Options -> Security" then tick all boxes except Encryption None and enter <b>/etc/ssl/cert.pem</b> in the "Path to X509 CA Certificate" field.  To save the settings click OK and then click Connect.  If Connect is not clicked the settings will not be saved.

First install TigerVNC viewer with the package manager for your linux version:

Next start TigerVNC by either finding it in the Applications menu or running <code>vncviewer</code> on the command line.  In the "VNC Viewer: Connection Details" window that appears click "Options -> Security" then tick all boxes except Encryption None and enter one of the following paths in the "Path to X509 CA Certificate" field.   

To save the settings click OK and then click Connect.  If Connect is not clicked the settings will not be saved.

Now you need a VNC server to connect to.  This can be either a persistent vncserver running on dedicated VDI Nodes which are part of [[Graham]], or a temporary vncserver you start on a cluster Compute Node.  VNC is not a heavyweight server, so you can certainly run lightweight sessions on cluster login nodes.

Graham has dedicated VDI nodes collectively known as gra-vdi.  These nodes provide a full graphical desktop, accelerated OpenGL, and shared  access to graham's <code>/home, /project,</code> and <code>/scratch</code> filesystems.

To connect start your desktop VNC viewer (tigervnc) and input the address '''gra-vdi.computecanada.ca'''. This should bring up a login screen where you can enter your Compute Canada credentials and login.

As with regular login nodes, the VDI nodes are a shared resource and not intended for doing batch computation (that is what the compute nodes are for) so please only use them for graphics-related tasks.  For example: graphical pre-processing such as mesh generation, graphical post-processing such as visualization, or graphical integrated development environments.

If you want to perform computational tasks within a gui please do so on a cluster compute node using the salloc command as described in the Compute Nodes section below.  This will ensure the memory and cpu resources on gra-vdi are fully available for interactive graphical visualization purposes by other users when needed.

Mac or Windows should click the <i>TigerVNC Viewer</i> application icon on their desktop and enter the '''localhost:port''' information in the Connection Details dialogue box that appears.  Keep in mind strict memory and cputime limits apply on cluster login nodes. On graham these are 8GB and 1 cpu-hour per process according to <code>ulimit -t -v</code>.  If you require more resources then run your VNC server on the VDI Nodes or Compute Nodes instead as described above and below respectively.

Where VDI login nodes are unavailable you can start a VNC server on a compute node, and, with suitable port forwarding, connect to it from your desktop.  This gives you dedicated access to the server, but does not provide a full graphical desktop or hardware-accelerated OpenGL.

Before starting your VNC server, login to a cluster (such as cedar) and create an allocation on a compute node using the <code>salloc</code> commmand (a 3hr maximum time limit applies). For example, to request an [[Running_jobs#Interactive_jobs|interactive job]] using 4 CPUs and 16GB of memory you could use the command:

Once your VNC server has been started, create a "bridge" to allow your local desktop computer to connect to the compute node directly. This bridge connection is created using an [[SSH tunnelling|SSH tunnel]]. SSH tunnels are created on your computer in a new local terminal window using the same SSH connection command as usual, with an extra option added - this follows the format: <code>ssh user@host -L port:compute_node:port</code>.

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To reset your VNC server password use the <code>vncpasswd</code> command:

If a vncserver is no longer needed terminate it with <code>vncserver -kill :DISPLAY#</code> as shown here:

If you have multiple vncservers running on a node, you may kill them all by running: <code>pkill Xvnc -u $USER</code>.

Repeated failure attempts to establish a new vncserver/vncviewer connection may be due to an old ssh tunnel still running on your desktop tying up ports.  To identify and kill any such tunnels, open a terminal window on your desktop and run <code>ps ux | grep ssh</code> followed by <code>kill PID</code>.

If your VNC screensaver times out and requests a password, enter your cluster account password to unlock it (not your vncserver password).  If you are running the MATE desktop and the screen saver will not unlock try running <code>killall -9 .mate-screensaver</code>.  This should no longer be a problem on Compute Canada clusters as the VNC screen saver has been disabled.

The VDI nodes have special hardware and virtual server configuration and extra layers of software modules compared to cluster Compute Nodes.  Therefore before running graphical software on gra-vdi its important to have a high level understanding regarding which software modules are available and will produce the best results before making a selection.

To install a nix package into your environment click the black terminal icon on the top menu bar or pick Applications -> System Tools -> Terminal.  Once a terminal window appears, run <code>module load nix</code>.  Now you can search for programs using the <code>nix search <regexp></code> command and install them in your environment using the <code>nix-env --install --attr <attribute></code> command.  As an example, to install [https://qgis.org QGIS] do the following:

The easiest way to do this is use the <code>patchelf</code> utility from nix (use <code>nix-env --install --attr nixpkgs.patchelf</code> to install it) to adjust the final binary.  For example, if you built an OpenGL application against the system libraries and installed it as ''~/.local/bin/myglapp'', then you need to add the system VirtualGL library ''/usr/lib64/VirtualGL/libvglfaker.so'' as the first required library.

Note that it is also possible to pre-load ''vglfaker.so'' via the <code>LD_PRELOAD</code> environment variable.  This is generally a bad idea as it applies indiscriminately to all binaries, and those that require a different ''vglfaker.so'' than that set in <code>LD_PRELOAD</code> will then fail, but it can be used safely in some cases in wrapper scripts.

Compute Canada software modules reside under /cvmfs and are available by default when you log into graham, cedar and beluga cluster.  These modules however are not loaded by default when you connect into gra-vdi over tigervnc.  To load them open a terminal window and run the following:

all Compute Canada software modules will now be available on gra-vdi identical to the clusters.  While these modules should always work reliably when running graphical applications on Compute Nodes some may have stability issues running on gra-vdi such as sudden crashing or strange graphical artifacts including transparent windows or missing menus.  To work around such problems use an equivalent package from nix as described in the previous section, better graphics performance may also be realized.  While the nix module provides a vast number of optimized/stable open-source packages for gra-vdi it does not provide commercial module equivalents for ansys, comsol or starccm. These can be found by loading the SnEnv module instead: