mental ray Shaders
Shader definition files (those ending in .mi) must go into either Maya's own mentalray/include directory or one of the directories in the user's MI_CUSTOM_SHADER_PATH environment variable.
Shader libraries (those ending in .so or .dll) must go into Maya's own mentalray/lib directory, or one of the directories in the user's MI_CUSTOM_SHADER_PATH environment variable, or one of the directories in the user's MI_LIBRARY_PATH environment variable.