From CMake setup 'make' to use '-j' option by default

Via setting the CMAKE_MAKE_PROGRAM variable you want to affect the build process. But:

1. This variable affects only the build via cmake --build, not on native tool (make) call:

   The CMAKE_MAKE_PROGRAM variable is set for use by project code. The value is also used by the cmake(1) --build and ctest(1) --build-and-test tools to launch the native build process.

2. This variable should be a CACHEd one. It is used in such way by make-like generators:

   These generators store CMAKE_MAKE_PROGRAM in the CMake cache so that it may be edited by the user.

   That is, you need to set this variable with

   set(CMAKE_MAKE_PROGRAM <program> CACHE PATH "Path to build tool" FORCE)
   

3. This variable should refer to the executable itself, not to a program with arguments:

   The value may be the full path to an executable or just the tool name if it is expected to be in the PATH.

   That is, value "make -j 2" cannot be used for that variable (splitting arguments as list

   set(CMAKE_MAKE_PROGRAM make -j 2 CACHE PATH "Path to build tool" FORCE)
   

   wouldn't help either).

In summary, you may redefine the behavior of cmake --build calls with setting the CMAKE_MAKE_PROGRAM variable to the script, which calls make with parallel options. But you may not affect the behavior of direct make calls.

In case you want to speed up the build you can run multiple make processes in parallel but not cmake. To perform every build with predefined number of parallel processes you can define this in MAKEFLAGS.

Set MAKEFLAGS in your environment script, e.g. ~/.bashrc as you want:

export MAKEFLAGS=-j8

On Linux the following sets MAKEFLAGS to the number of CPU - 1: (Keep one CPU free for other tasks while build) and is useful in environments with dynamic ressources, e.g. VMware:

export MAKEFLAGS=-j$(($(grep -c "^processor" /proc/cpuinfo) - 1))