Installing O2 and O2Physics

ALICE software has several dependencies: aliBuild takes care of downloading them for you. aliBuild can also automatically download precompiled binaries if possible.

Installing aliBuild

Follow the instructions here. Do not follow "build the packages" on that page.

Prepare your source code

We assume your work area is ~/alice. Start with a clean shell where you are not in an alienv environment. Create the directory and move to it (all the following commands need to be executed in this folder):

mkdir -p ~/alice
cd ~/alice

Download O2 and O2Physics:

aliBuild init O2@dev
aliBuild init O2Physics@master

If you perform ls under your work directory, you will see the packages you have downloaded via aliBuild init, plus an alidist directory.

The alidist directory contains software recipes, telling aliBuild how the software is built. Your alidist directory and your software source code are Git directories managed by you: you need to keep them up-to-date manually.

Check your prerequisites

aliDoctor O2Physics

aliDoctor will warn you that some packages have to be built as they could not be found from the system.

Build and rebuild

aliBuild build O2Physics

See the Troubleshooting section for debugging tips if the build fails.

Use your local software installations

You will not find the packages you have built immediately available on your shell: we provide a tool called alienv that configures your shell according to the packages you want to load. alienv is capable of switching between different versions of the same package without a hassle.

List your available packages with:

alienv q

Load the latest version you have built of a package (O2Physics for instance):

alienv enter O2Physics/latest

⚠️ Dependencies are loaded automatically. Do not attempt to load O2 or ROOT as well, you will find them automatically in the environment! alienv enter is verbose and will inform you about the loaded packages if you have doubts.

The alienv enter command drops you to a new shell. Unload the packages by simply exiting it with the exit command.

Building partially for development using ninja

This requires that the O2Physics build succeeded. Enter the environment as explained in the previous step specifying in addition the ninja package:

alienv enter O2Physics/latest ninja/latest

Go to the build directory

cd ~/alice/sw/BUILD/O2Physics-latest/O2Physics

You can now rebuild and install entire O2Physics with

ninja install

or just a specific directory with

ninja <directory>/install

For example:

ninja PWGCF/Tasks/install

You can redirect the terminal output to the standard aliBuild log file and see whether the build succeeded:

ninja install > ../log 2>&1 && echo "Good" || echo "Bad"

A specific executable can be built in the staging directory stage/bin with

ninja stage/bin/<target>

For example:

ninja stage/bin/o2-analysis-cf-correlations

The executable can then be executed directly from the staging directory:


This only builds O2Physics. If you have updated O2 or alidist, you first need to do a full build with aliBuild. Then enter the environment again before using ninja.