🛠 Build the packages

ALICE software has several dependencies: aliBuild takes care of downloading them for you. aliBuild will also automatically download precompiled binaries on supported versions of CentOS/Alma and Ubuntu.

aliBuild will download and compile all the dependencies caching data under $ALIBUILD_WORK_DIR. You will never need to access this directory. The source code for the packages you will actually develop will be stored elsewhere.

In the following example, we will assume that you need to download AliRoot/AliPhysics for developing Run 2 software, and O2/O2Physics for Run 3.

Prepare your source code

We assume your work area is ~/alice. So, first off, create the directory and move to it:

mkdir -p ~/alice
cd ~/alice

If you need to develop for Run 3, download O2Physics:

aliBuild init O2Physics@master

Only if you need to develop the Run 3 core software (unlikely), download O2:

aliBuild init O2@dev

aliBuild init AliPhysics@master

Source code and recipes

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.

Update your software by cding into its directory and running:

# use dev instead of master for O2
git checkout master
git pull --rebase upstream master

This will work in most cases and will keep your changes. It will also complain if there is some conflict you need to solve manually. You also have the nuclear option, to be used if you are sure you do not have any important data:

# use dev instead of master for O2
git checkout master
git fetch --all
git reset --hard upstream/master

Instead of resetting to the current upstream version, you may want to download specific versions of the software:

cd ~/alice/O2
git fetch --all --tags
git checkout v5-09-42-01

Check your prerequisites

aliBuild comes with the command aliDoctor that will help you identifying if your prerequisites were installed correctly. In general, aliBuild is capable of building all required software dependencies, but it has also the ability to take them "from the system" if possible, resulting in less time spent for building for you.

For Run 3 software:

cd ~/alice
aliDoctor O2Physics

aliDoctor will warn you that some packages have to be built as they could not be found from the system. If you have followed the instructions, this list should contain nothing more than:

• boost
• CMake
• GSL
• nanomsg
• protobuf
• flatbuffers
• Vc
• yaml-cpp
• ZeroMQ
• SWIG

In particular, you should never have Python or Python-modules. If the output is longer than this list, please go through the prerequisites once again and run aliDoctor again. If the output contains those packages, or less packages, then you are fine and you may continue.

If you think a package is shown but should not be in the list because you are sure you have installed it, it might just be that its version it's incompatible (this frequently happens with CMake) or you are missing the "development" package for that component.

cd ~/alice
aliDoctor AliPhysics

Build and rebuild

You can build the whole Run 3 software stack with :

cd ~/alice
aliBuild build O2Physics

If you want to build O2 and run the tests as well (same way as they are run on the pull request checkers), with --debug to see the full output:

cd ~/alice
aliBuild build O2 --debug -e ALIBUILD_O2_TESTS=1

⚠️ It is recommended to run the first O2 build without the tests enabled to let it complete. You will not have to rerun it from scratch because of test failures like this.

Using the combinations above on CentOS 7 will make aliBuild automatically download the precompiled binaries for almost all packages.

cd ~/alice
aliBuild build AliPhysics

Rebuild existing installations

As a general rule, your existing installation can be smartly rebuilt by using the exact same aliBuild build command as you did the first time. aliBuild will not rebuild existing software and it will simply rebuild the changes.

You may find it fast to skip the aliBuild part completely. You can simply move to the build directory and run make (the alienv part is explained later):

cd $ALIBUILD_WORK_DIR/BUILD/AliPhysics-latest/AliPhysics
alienv setenv GCC-Toolchain/latest -c cmake --build . -- -j <num-parallel-jobs> install

Replace <num-parallel-jobs> with a sensible number (e.g. slightly more than the actual number of your cores).

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 (AliPhysics for instance):

alienv enter O2/latest

⚠️ Dependencies are loaded automatically. Do not attempt to load O2 and 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.

Load environment in the current shell or script

If you know what you are doing, you can also load the environment in your current shell, and subsequently unload it (this is not recommended):

alienv load O2/latest
alienv unload O2/latest

If you want to load the environment inside a script you are developing, just add this line (works with Bash scripts):

source $(alienv printenv O2/latest)

Run a single command in the environment

You can also run a single command (for instance, root) in the given environment without loading it in the current shell:

alienv setenv O2/latest -c root

Special build needs

Please refer to the aliBuild documentation for special build options like:

• Building multiple branches in the same area
• Remove obsolete / unneeded packages
• Limit resource usage
• Cross platforms builds using docker / Apple Container