cmake error when compiling ros_rt_wmp

ERROR:

mkdir -p bin

cd build && cmake -Wdev -DCMAKE_TOOLCHAIN_FILE=/core/rosbuild/rostoolchain.cmake ..

CMake Error at /usr/share/cmake-2.8/Modules/CMakeDetermineSystem.cmake:95 (MESSAGE):

    Could not find toolchain file: /core/rosbuild/rostool.chain.cmake

Call Stack (most recent call first):

CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.

Missing variable is:

CMAKE_C_COMPILER_ENV_VAR

CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.

Missing variable is:

CMAKE_C_COMPILER

.....

SOLUTION:

Since $echo $ROS_ROOT, there is no result.

We $export ROS_ROOT=/opt/ros/groovy/share/ros

Then the "make" compilings are successful.