A minimum required CMake version must be specified.

CMake requires that projects specify the version of CMake to which they have been written. This policy has been put in place so users trying to build the project may be told when they need to update their CMake. Specifying a version also helps the project build with CMake versions newer than that specified. Use the cmake_minimum_required command at the top of your main CMakeLists.txt file:

cmake_minimum_required(VERSION <major>.<minor>)

where “<major>.<minor>” is the version of CMake you want to support (such as “2.6”). The command will ensure that at least the given version of CMake is running and help newer versions be compatible with the project. See documentation of cmake_minimum_required for details.

Note that the command invocation must appear in the CMakeLists.txt file itself; a call in an included file is not sufficient. However, the cmake_policy command may be called to set policy CMP0000 to OLD or NEW behavior explicitly. The OLD behavior is to silently ignore the missing invocation. The NEW behavior is to issue an error instead of a warning. An included file may set CMP0000 explicitly to affect how this policy is enforced for the main CMakeLists.txt file.

This policy was introduced in CMake version 2.6.0.