Environment Variables

Environment variables can be set from a shell prompt with shell commands such as setenv (see the documentation of your shell) before mental ray, or the application that mental ray is built into, is started from the same shell. Environment variables set after mental ray is started, or set from a different shell, have no effect. mental ray will work without any environment variables, except that the .rayrc startup script may not be found if MI_ROOT is undefined.

DISPLAY: The Unix X11 display to be used for OpenGL acceleration.
HOME: Unix home directory, for finding the user's local .rayrc file.
HOMEDRIVE: Windows NT home drive, such as C:.
HOMEPATH: Windows NT home directory. mental ray will try to load %HOMEDRIVE%/%HOMEPATH%/rayrc.
MI_ASSEMBLY_PATH3.6: A colon-separated or semicolon-separated list of paths to search for assembly .mi files referenced in a assembly.
MI_CG_FRAGMENT_PROFILE: Pass this profile name to the Cg compiler when compiling hardware shaders, instead of the profile matching the graphics hardware rendered on. This is useful in conjunction with the -hardware_echo command-line option to "cross-compile" shaders.
MI_HWDISPLAY: Overrides DISPLAY. This is useful if mental ray is run on one machine, where all graphical user interfaces are shown (so DISPLAY must point to the local host), but the local host does not have sufficient hardware rendering capacity so mental ray offloads it to another host, pointed to by MI_HWDISPLAY. This kind of remote hardware rendering incurs extra networking overhead but allows multiple desktop clients to share a fast hardware rendering server. It is not necessary for mental ray to be installed on the server, and no extra license is used. However, both the client and server hosts must have compatible OpenGL and OpenGL extension versions.
MI_LIBRARY_PATH: A colon-separated or semicolon-separated list of paths to search for files loded with the link command.
MI_RAY_HOSTSFILE: Use this file name instead of the default .rayhosts to read host configuration for distributed rendering.
MI_RAY_INCPATH: A colon-separated or semicolon-separated list of paths to search for files included with the $include command.
MI_RAY_OPTIONS: Extra options that are inserted by mental ray before the options on the command line. This is commonly used for options such as -xcolor.
MI_RAY3_SERVICE: The IP service that mental ray uses to contact slaves on other machines. The default is mi-ray3 for mental ray 3.x. On Unix, service names are defined in /etc/services or in the services NIS map.
MI_RAY_SERVICE: If the previous variable is not defined, this one is used instead. This makes mental ray 2.x compatible with mental ray 1.9 while allowing both to coexist on the same machine. The default is mi-ray.
MI_RAY_SUBSTITUTE: An optional list of blank-separated substitution instructions, each in the form /search/replace/. Any other character besides / will also work.
MI_RAY_SWAPDIR: A swap directory where mental ray can temporarily store scene elements in files on disk when main memory runs out. This can be useful to render large scenes where other caching mechanisms are not enabled. mental ray generally swaps more efficiently than the operating system.
MI_RAY_SWAPLIMIT: The maximum number of bytes to write into the swap directory. A value of 0 turns off swapping.
MI_ROOT: The directory that mental ray searches for configuration files such as rayrc.
MI_STACKSIZE: New thread stacks will be created with this size in kilobytes if defined. The default is 16384 (16 MB) on Unix and 4096 on Windows. 4096 is nearly always sufficient except when very complex recursive shaders are used.
MI_TEX_LOOKUP_LOCAL: This variable can be set in network parallel rendering in order to look up and remap texture file paths on the individual rendering hosts instead of on the master host only. This allows to locate textures on the slave machines at a different file system path than on the master host.; Note that MI_TEX_LOOKUP_LOCAL should be set on all rendering hosts, not just the master.; Note also that this also causes file names to be echoed in the .mi format without performing file path substitutions.
SI_LOCATION: The directory of the linktab.ini file, which may be used by applications to customize file path mapping.
TMPDIR: A directory for temporary code or object files to be compiled or linked. The default is /usr/tmp on Unix and the current directory on Windows.
USER: The current user name. This is optional, and if it exists may be stored in image file headers, for example.

The mental ray registry supports lookups of environment variables. The form $var returns the value of the environment variable var, and $?var returns 1 if the environment variable var exists and 0 otherwise.