# CMAKE_FASTBUILD_CAPTURE_SYSTEM_ENV

Added in version 4.2.

Controls capturing of the system environment into `fbuild.bff`. Setting it to `OFF` makes the invocation of all tools (compilers and other external processes) hermetic.

Note

Setting this variable to `OFF` can break MSVC toolchains that rely on environment variables such as `INCLUDE` or `LIB` unless these are manually configured elsewhere.

Defaults to `ON`.