step_by_step_instructions.md

Building ROOT for ROOT developers, step by step

1. Forking the root and roottest repositories

You need to have your own forks of the repositories in order to propose modifications in the form of GitHub PRs. In some cases the modifications will need to go in roottest, so it's better to clone both. Go on the respective websites:

• https://github.com/root-project/root
• https://github.com/root-project/roottest

And click on the Fork button in the top right of the web UI.

2. Clone the repositories and track the upstream git remote

You can now clone both repositories on your machine, e.g. via

$: git clone https://github.com/YOURUSERNAME/root.git
$: git clone https://github.com/YOURUSERNAME/roottest.git

To track changes in the main repositories, add the upstream remotes.

Inside the root directory:

$: git remote add upstream https://github.com/root-project/root.git

Inside the roottest directory:

$: git remote add upstream https://github.com/root-project/roottest.git

3. Create build and install directories

To keep things clean, it is suggested to create separate directories for the builds and for the installations.

$: mkdir rootbuild rootinstall

4. Configure the CMake build

There are many configuration options. For the purposes of development and testing, the following configuration is suggested:

$: cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo -Dtesting=ON -Droottest=ON -DCMAKE_INSTALL_PREFIX=rootinstall/myinstall -B rootbuild/mybuild -S root

The process of launching the Cmake build may be sped up by using the ccache package, if it is installed in the system. To activate it, add -Dccache=ON to variables.

5. Build and install

Finally, you can launch the CMake build via:

$: cmake --build rootbuild/mybuild --target install -jNPROC

Where NPROC is the number of available cores you want to send in parallel for the build.