This section lists some common problems when using the CAVE, and some steps to hopefully solve them.

Trouble Shooting Updates - May 1, 2009

If a CAVE application does not start up when double-clicking its icon in the “CAVE Demo Programs” folder, this can be for a variety of reasons. To pinpoint the actual problem, one should go through the following diagnostic steps:

To show the current state of the cluster nodes, double-click on the “Cluster Monitor” icon on the desktop. This will open a window with CPU usage gauges for all cluster nodes (caveman with two CPUs, r1-r5 with one CPU each). Normally, all bars should be green (denoting idle CPUs), with an occasional flash of red or blue. Once the status of the cluster is affirmed, the monitor window can be closed again.

If the cluster monitor window does not open, this means that at least one cluster node is not responding. At this point, it is best to call for help.

There should already be at least one terminal window on the desktop; otherwise, one can be opened by clicking on the terminal icon in the panel bar at the bottom of the desktop (third icon from the left). To type into the terminal window, the mouse cursor needs to be moved inside (typing works if the terminal window's title bar is dark blue). To change into the CAVE applications directory, type cd ~/Demos. The terminal prompt will now read caveman:~/Demos.

Sometimes when a CAVE application crashes, its child processes on the cluster nodes do not shut down. While these “zombie processes” are running, no other CAVE application can start. To check for zombie processes, open a terminal and type ListAllNodes. This script will print the names of all processes running on the cluster nodes (nodes r1-r5). If any zombie processes show up, they can be terminated by typing KillAllNodes.

The driver for the input device hardware is a stand-alone process that is automatically started at boot up and should never terminate. Unfortunately, it sometimes does. To check whether the device driver is running, type CheckDeviceDriver. If the script prints anything but VRDeviceDaemon (pid <some number>) is running… the device driver terminated and needs to be restarted. To restart the device driver, type sudo RestartDeviceDriver. This will prompt for the user's password, and then attempt to shut down the device driver (which will fail), followed by starting it again. Afterwards, the driver's status can be checked again by typing CheckDeviceDriver, and its log file can be inspected by typing cat /var/log/VRDeviceDaemon.log. The latter should print text that should end with a line stating VRDeviceServer: Waiting for client connection

If either of these two checks fails after the device driver has been restarted, there is something wrong with the input device hardware. At this point, it is best to call for help.

Even when the input device driver runs, it might still not react to connections. To run a test program, type TestInputDevices. If the input devices are functioning, this should print the (x, y, z) position of the wand device in inches relative to a spot in the center of the CAVE floor. If the wand is turned on, the numbers will be updated several times per second. To finish the test program, press Enter.

If this test fails, and restarting the device driver does not help, there is something wrong with the input device hardware. At this point, it is best to call for help.

To check if the video cards in all cluster nodes are working, start the display control program by double-clicking on the “Video Card Control” icon on the desktop. Note: Improper use of the display control program can cause serious trouble. Please be careful to not make any accidental changes to any settings. If the program does not start, the cluster nodes' X servers might be down. At this point, it is best to call for help. Otherwise, the display control program should be closed again (it affects performance of CAVE applications if left running).

New account and post-upgrade ssh problem

Since most CAVE applications are prototypes and still under development, any of them might crash at any given time. Due to the CAVE computer system's cluster nature, the operating system can not always automatically clean up after a misbehaving application. Crashes come in three flavors:

1. “Hangs” or “Locks”: The application seems to “freeze”; and does not react to input anymore. The application's console window is still open, and the CAVE walls do not show the background image.
2. Console crashes: The application's console window is closed, but all CAVE walls still do not show the background image.
3. Wall crashes: One or more of the CAVE walls show the background image, but the application's console window is still open.

In all cases, the first thing to do is to remove all remnants of the misbehaving application. Each application runs as a separate process on the console computer and the render nodes, and if only some of those processes crash, the others are stuck, but still running. The following steps will remove all “hung” application processes:

1. Check if the console computer is reacting to mouse movements and/or key presses. If the console computer appears frozen, something is seriously wrong, and it is best to call for help.
2. Open a terminal window.
3. Type ListAllNodes. This shows all VR application processes, running on the console computer (caveman) and the render nodes (render-1 to render-5).
4. Type KillAllNodes. This will kill all VR application processes on all CAVE computers.
5. Check if the application's console window is gone, and if the CAVE walls show the background image again. If this is not the case, something is seriously wrong, and it is best to call for help.
6. Check if the VR device driver is still running, as described in the previous section. Sometimes a crashing application takes the device driver with it, sometimes a locked device driver causes an application to appear frozen. Try the TestInputDevices command first, and then the other steps if it fails.

If the image on the screen appears “warped” or does not change when a user moves her/his head, the head tracker might not be able to communicate with the tracking rails (above the CAVE, with the blue “blinkenlights”). The head tracker has two tiny microphones on the top front corners. The tracker will not work properly if the microphones are obstructed, for example by a visor. (Although not recommended as a fashion statement, it is advisable to wear baseball caps backwards, or not at all.)

If the image on the screen appears “double” and there is no depth perception, the stereo glasses might not be able to communicate with the projectors. The stereo glasses are controlled via an infrared signal; the infrared receiver is located between the eye glasses. The line of sight between the receiver and the projectors (behind the screens) must not be obstructed (headgear advisories apply as above). Sometimes the glasses do not turn on properly; in that case, taking them off, folding, and unfolding them again usually fixes the problem.

If CAVE applications are working, but the display flickers badly when looking at a corner between two or three screens, or there is no depth perception at all, the CAVE screens might have lost synchronization. To run the display control program, double-click on the “Video Card Control”; icon on the desktop. Note: Improper use of the display control program can cause serious trouble. Please be careful to not make any accidental changes to any settings. In the display control program's window, select the “FrameLock” section in the list on the left. This will change the right side of the window to show a list of all render nodes (r1-r4). If the list does not show up completely, enlarge the program's window vertically by pulling on the lower window border with the mouse. In the list of render nodes, all lines should show green bullets in the “Stereo Sync” and “Sync Ready” columns, and all but the master render node (r2) should show green bullets in the “Timing” column. If this is not the case, or the button on the lower right of the window reads “Enable FrameLock” restart synchronization by clicking on the button on the lower right of the window once or twice, until it reads “Disable FrameLock”. After this, the bullets in the list will change color, and after a few seconds all of them should be green again. At this point, the display control program should be closed again (it affects performance of CAVE applications if left running).