Building ROOT from source¶

ROOT 6 uses a CMake based build system. The build process consists of three steps:

1. Running cmake with the desired configuration arguments in a "build directory," which is separate form the source directory
2. Executing make to build the package
3. Doing make install to copy the relevant subset of sources and generated binaries to the installation directory

Step 1. is the most difficult one since one has to pick appropriate configuration options, of which ROOT has many. A detailed description of all options can be found on the relevant documentation page. Let us walk through a typical build process here.

1. Make sure that your system compiler is at least gcc 4.8. It needs to support C++11 fully. If you do not have such a compiler, you should upgrade your system, unless you have a lot of patience and skill. On rpm-based Linux distributions, the gcc-c++ and libstdc++ packages need to be installed. To fin dout your compiler version:
   

   $ g++ --version
   g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-28)
   ...
   

2. Verify that you have at least CMake version 3.4.3. On some systems, this command may be called cmake3. On RHEL7/CentOS 7, cmake3 is availale from EPEL.
   

   $ cmake --version
   cmake version 3.11.1
   

3. Download the ROOT source tarball from the download page. Always pick the latest production ("pro") version; it should work even on old platforms.
4. Unpack the source distribution wherever you like. This will create a subdirectory named "root-<version>".
   

   $ tar xf root_v6.12.06.source.tar.gz
   $ ls
   root-6.12.06
   

5. Create and switch to the build directory, for example
   

   $ mkdir -p ~/Develop/BUILD/root
   $ cd ~/Develop/BUILD/root
   

6. Now prepare to run cmake to configure ROOT. This step will automatically detect if required dependencies are available. The most important dependencies are bundled with ROOT and are built automatically if they are not detected on the host system. Other dependencies are optional; if not found, the corresponding feature in ROOT is automatically disabled. (Example: MySQL database support.) You will get a functional version of ROOT even without these optional dependencies, so it is not essential to provide them. Getting them installed is best done through your system's package manager. Some obscure dependencies need to be build by hand from source first, which can be very time-consuming. Here's a basic CMake command that should give good results on most systems:
   

   $ cmake -DCMAKE_INSTALL_PREFIX=<path-to-where-you-want-ROOT-to-be-installed> -D.... <path-to-unpacked-ROOT-source>
   

(to be continued)