Environment Variables

Several environment variables are used by VMD to determine the location of certain files and directories. These variables are accessible to text interface through array env. These variables include:

• DISPLAY : (Unix-only) The X-Windows display that VMD should use for displaying the VMD windows and menus, as well as the graphics window. If this environment variable is not overridden by VMDGDISPLAY all VMD windows will be directed to this display.

• VMDDIR : The directory which contains the VMD data files (such as this help file) and architecture-specific executables. By default, this is /usr/local/lib/vmd on Unix systems, and C:\Program Files\University of Illinois\VMD on Windows sytems.

• VMDTMPDIR : The directory which VMD should use for temporary data files. By default, this is /tmp, or /usr/tmp on Unix systems, and C:\ on Windows.

• VMDCUSTOMIZESTARTUP : (Unix-only) The name of a C-shell script to source prior to running the actual VMD process. This shell script can contain any commands necessary for performing machine-specific spaceball, graphics, and other customizations necessary to run VMD. This can be anything from a simple script that sets the right serial port for a Spaceball based on the hostname, or it can be a complex script for turning on a projection system, logging demos, configuring multi-display stereo-framelock features, etc.

• VMDBABELBIN : The complete path and filename for the program babel, which is used by VMD to convert molecular structure/coordinates files into PDB files which VMD can actually understand. If this is not set explicitly, the VMD startup script will attempt to find babel in the current path. If Babel cannot be found or is not installed, VMD will not be able to read molecular file formats other than PDB, PSF, and binary DCD files.

• VMDFILECHOOSER : Specifies which file chooser to use for loading and saving files from the GUI. At present, this should be either FLTK, which uses Fltk's platform- independent file chooser, or TK, which uses Tk's file chooser. The Tk file chooser is the default and uses a native Windows interface on Windows platforms. The Fltk file chooser looks the same on all platforms, supports tab completion but not drive letters, and is probably most appropriate for Unix environments. The file chooser can be overridden at any time by changing the environment variable (e.g., in Tcl, set env(VMDFILECHOOSER) FLTK).

• VMDFORCECPUCOUNT : Specifies the maximum number of CPUs or CPU cores that VMD should use when running on a multiprocessor or multicore computer system. By default, VMD will use all of the processors on the host machine. This option can be used to prevent VMD from ``hogging'' CPUs or to make it abide by job submission policies required on large supercomputer systems, when running batch mode.

• VMDCAVEMEM : (Unix-only) This overrides the default size of the shared memory arena which is allocated by VMD when the CAVE starts up. The variable must be an integer number of megabytes. Since this is the only shared memory pool allocated, and it is done only once, you must choose a value sufficient to account for the largest scene you intend to render in VMD in that CAVE session. The default value unless otherwise specified is 80 Megabytes. Values of 200MB to 512MB are commonly needed for large molecular systems containing several hundred thousand atoms.

• VMDFREEVRMEM : (Unix-only) This overrides the default size of the shared memory arena which is allocated by VMD when the FreeVR starts up. The variable must be an integer number of megabytes. Since this is the only shared memory pool allocated, and it is done only once, you must choose a value sufficient to account for the largest scene you intend to render in VMD in that FreeVR session. The default value unless otherwise specified is 80 Megabytes. Values of 200MB to 512MB are commonly needed for large molecular systems containing several hundred thousand atoms.

• VMDFORCECONSOLETTY : (Unix-only, intended only for clusters This environment variable forces VMD to treat the text console as an interactive terminal, despite what the operating system says. This is only useful for running an interactive VMD session on a Clustermatic or Scyld Linux cluster node.

• VMDGDISPLAY : (Unix-only) The name of an X-Windows display that VMD will use to display the graphics window. This environment variable is only used on Unix systems. Through the use of the the DISPLAY and VMDGDISPLAY envrironment variables, the VMD graphics window can be placed on a separate screen from the windows and menus. This is particularly useful when giving 3-D demonstrations using a projector. The windows and menus can be kept on a different screen from the graphics so that they do not distract the audience.

• VMDGLSLVERBOSE : OpenGL Shading language compiler diagnostic errors only printed only when this environment variable is set.

• VMDHTMLVIEWER : The name of a command that will run a web browser in the background (Netscape, Mozilla, Firefox or whatever you prefer) that VMD should use to display HTML documents (such as this help file). By default, on UNIX, this is mozilla. (usage examples in Tcl: set env(VMDHTMLVIEWER) ``mozilla -remote openURL(%s)", set env(VMDHTMLVIEWER) ``mozilla %s SPMamp;")

• VMDIMAGEVIEWER : The name of the external program to use for displaying VMD snapshots (or other images), in various formats.

• VMDIMMERSADESKFLIP : Enable a special reversed/reflected stereo projection mode for use with experimental displays based on LCD panels, phase plates, and beam splitters.

• VMDVMDMACENABLEEEXTENSIONS : Enable performance-oriented OpenGL rendering extensions which are disabled by default. These extensions have been observed to trigger instability on some MacOS X systems.

• VMDMSECDELAYHACK : Add in a user-specified delay which causes VMD to sleep for specified number of milliseconds each time it renders the molecular scene on the display. This feature is meant as a workaround to poor performing display drivers which make the windowing system unresponsive if VMD is allowed to run unrestricted at maximum drawing rate.

• VMDMSMSUSEFILE : Force VMD to communicate with MSMS through the filesystem rather than with the socket-based network interface. This option can be used when the socket interface isn't working properly for some reason. This is the default behavior when using VMD on Windows.

• VMDNOCUDA : Force VMD not to use CUDA-based GPU acceleration, even if CUDA support was compiled in, and CUDA-capable devices are detected at startup. This can be used in cases where a GPU or GPU drivers prove to be unreliable for computation, for benchmarking vs. CPU-only implementations, and to prevent VMD from using a GPU that's already oversubscribed by other processes running on the same machine.

• VMDDISABLESTEREO : (Unix) Prevents VMD from enabling stereoscopic display features. This is normally only used as a workaround for buggy display drivers.

• VMDPREFERSTEREO : (Unix, MacOS X) On Unix systems using X11, this environment variable allows NVidia Quadro users to override the normal X11 visual search order, skipping multisample capable visuals in favor of stereo visuals. VMD still attempts to get the more complex visuals first, but if it comes down to a choice between stereo and multisample as mutually exclusive options, this variable provides the ability to force the use of stereo if available. On MacOS X, this environment variable tells VMD to create a a stereo-capable display window, even at the risk of terminating the program if the request is denied.

• VMDSCRDIST : Distance to the VMD image plane.

• VMDSCRHEIGHT : Height of the VMD image plane.

• VMDSCRPOS : Position of the VMD graphics window (x,y).

• VMDSCRSIZE : Size of the VMD graphics window (x,y).

• VMD_EXCL_GL_EXTENSIONS : Disable the use of named OpenGL extensions according to their official OpenGL extension names. This is intended to be used only when one encounters severe stability problems caused by buggy display drivers.

• VMDSHEARSTEREO : Enable the use of an alternative perspective projection mode which may result in improved stereoscopic display. Uses the shear-matrix stereo formulation rather than eye rotation.

• VMDSIMPLEGRAPHICS : Forces VMD to use absolutely minimalistic graphics features with no use of OpenGL extensions. Essentially, nothing but bread-and-butter vertex arrays and immediate mode rendering will be used. This mode is intended to be used only when one encounters severe stability problems caused by buggy display drivers.

• VMDWIREGL : This environment variable disables several graphics features which are unsupported (or poorly supported) by WireGL and Chromium. This variable will be superceded with a more general implementation in a future release.