# 🛠 Build the packages

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 want to develop analysis code, download AliPhysics: aliBuild init AliPhysics@master  Only if you need to develop the Run 2 core software (unlikely), download AliRoot: aliBuild init AliRoot@master  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  ### 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. ### Check names of your remote repositories With older versions of aliBuild, the central remote repository (used for pulling updates) would be called origin instead of the usual name upstream and the personal (fork) remote repository (used for pushing changes) would be called <your-github-username> instead of the usual name origin. Please check your settings using git remote -v and adjust the Git commands mentioned in the following instructions accordingly, if needed. 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/AliPhysics git fetch --all --tags git checkout v5-09-42-01  ### Why manual updates? Software downloaded under your working directory is your responsibility. Our tools will not take any action to update it: imagine if you lose important data because of an automatic update! As a developer, and ALICE contributor, you must be capable of using and understanding git. ## 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. Run the aliDoctor command to check dependencies for Run 2 software: cd ~/alice aliDoctor AliPhysics  For Run 2 software based on ROOT 6 (note: this is the only option on macOS): cd ~/alice aliDoctor AliPhysics  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. ## Build and rebuild You can build the whole Run 2 software stack based on ROOT 6 with: cd ~/alice aliBuild build AliPhysics  Similarly, for O2Physics: 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. ### AliPhysics with ROOT 6 and the Grid The command above will produce AliPhysics with ROOT 6 as a dependency. When using this version, you will only be able to submit Grid analysis jobs using ROOT 6-based builds (whose name ends with _ROOT6). If you still need ROOT 5 only for submitting Grid jobs, there is no need to install it: just use it from CVMFS by logging in to lxplus.cern.ch. ### Other build options The options above are suitable for a CentOS 7 installation, since precompiled binaries will be downloaded. You also have other installation options according to your needs: it is not guaranteed that cached binaries are available for the following options, but they may be faster to build. Build AliPhysics based on ROOT 5 (legacy): aliBuild build AliPhysics --defaults user # without GEANT 3, GEANT 4, DPMJET aliBuild build AliPhysics --defaults release # full ROOT 5 stack  ⚠️ ROOT 5 does not work on macOS. Use a ROOT 6 version compatible with ROOT 5 if you really need it (see below). ### 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).

### You lied. aliBuild is rebuilding everything! 🤬

One or more of the following actions might change the way aliBuild sees and uses the dependencies and might result in a full (or nearly) rebuild. So, if an important conference is approaching (well: it always does, doesn't it?) plan the following actions accordingly as they might increase the build time:

• Updating recipes in alidist
• Removing the cache $ALIBUILD_WORK_DIR or forgetting to export the variable • Adding or removing system dependencies as seen by aliDoctor • Updating your operating system or compilers (including Xcode on macOS) ## Use your local software installations You will not find the packages you have built immediately available on your shell: we provide a tool called alienv that configures your shell according to the packages you want to load. alienv is capable of switching between different versions of the same package without a hassle. List your available packages with: alienv q  Load the latest version you have built of a package (AliPhysics for instance): alienv enter AliPhysics/latest  ⚠️ Dependencies are loaded automatically. Do not attempt to load AliRoot and ROOT as well, you will find them automatically in the environment! alienv enter is verbose and will inform you about the loaded packages if you have doubts. The alienv enter command drops you to a new shell. Unload the packages by simply exiting it with the exit command. ### I have several AliPhysics versions. Which one is AliPhysics/latest? aliBuild will tell you exactly what you need to type in order to load the software you have just built. Just use aliBuild's suggestion in place of AliPhysics/latest wherever appropriate: for instance, if you have several AliPhysics versions, AliPhysics/latest will point to the version you have built more recently, not the latest. ### Load environment in the current shell or script If you know what you are doing, you can also load the environment in your current shell, and subsequently unload it (this is not recommended): alienv load AliPhysics/latest alienv unload AliPhysics/latest  If you want to load the environment inside a script you are developing, just add this line (works with Bash scripts): source$(alienv printenv AliPhysics/latest)


### Run a single command in the environment

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

alienv setenv AliPhysics/latest -c aliroot myMacro.C+


Even if this is technically possible, it is strongly not recommended to load the environment with alienv in your ~/.bashrc! You must keep your environment pristine for safely running aliBuild. By not loading the environment automatically, you will avoid a huge source of errors.

Do you still find annoying to type alienv enter AliPhysics/latest every time you want to use it? You can add the following line in your ~/.bashrc to make it more convenient:

alias ali='alienv enter AliPhysics/latest'


You are creating an alias called ali, that will load the environment by just typing it at the prompt. Of course you can name it any way you want.

## Special build needs

### Build by using less resources

Building takes by default all the available CPU and most of the memory of your computer, considerably slowing down your work. In some cases you may want to reduce the number of cores available to aliBuild by using the -j <num-cores> option:

aliBuild build AliPhysics -j 1


### Do not use the cache on CentOS 7

aliBuild will attempt to fetch the precompiled binaries automatically on CentOS 7: no need to specify extra options.

If you want not to use them for some reason, it is important you follow the CentOS 7 prerequisites first: this will allow aliBuild to take as many packages as possible from the system. You will then need to add the --always-prefer-system option to the aliBuild build command. For instance:

aliBuild build AliPhysics --always-prefer-system


### Build the same source multiple times with different options

aliBuild and alienv give you the ability to build the same development source with different defaults without duplicating the source, and without conflicts.

Imagine we are under ~/alice and we have cloned AliRoot and AliPhysics with the aliBuild init command above. We build AliPhysics twice, once with ROOT 5 and a second time against ROOT 6.

Let's first build AliPhysics with ROOT 5:

aliBuild build AliPhysics --defaults user -z aliroot5


⚠️ Note the -z aliroot5 command; it is assigning a nickname to the build for distinguishing it more easily when using it.

The command ends with a message saying what to do to use the package:

alienv enter AliPhysics/latest-aliroot5-user


Let's now build the same AliPhysics with ROOT 6:

aliBuild build AliPhysics -z aliroot6


Now, the message tells us to type:

alienv enter AliPhysics/latest-aliroot6-o2


Keep in mind that:

• aliBuild always tells you what is the package name to load at the end of the build
• you can load the two environments separately, in two different shells, with no chance of a mixup
• you have used the same set of sources for generating two distinct builds
• alienv enter AliPhysics/latest will load the latest you have built, which can either be the ROOT 5 or ROOT 6-based version: given its ambiguity, do use explicit names instead

It is also possible to directly run aliroot (or any command you want) without "entering" the environment:

alienv setenv AliPhysics/latest-aliroot5-user -c aliroot
alienv setenv AliPhysics/latest-aliroot6-o2 -c aliroot


The aliroot command will be run with the correct environment in both cases.

### Migrating from ROOT 5 to ROOT 6

While you are at it, if you want to migrate your existing code to ROOT 6 (and make sure it works there) check out our migration guide.

### Build specific releases (tags) of the software

It might come useful to build a certain tag of AliRoot and AliPhysics instead of simply pulling the master.

Note that we only guarantee that the current AliPhysics master works against the latest AliRoot tag! It is therefore possible (though a rare occurrence) that the current AliRoot master breaks the current AliPhysics master.

If you have your source code in "development mode" (i.e. downloaded locally by means of aliBuild init), since your AliRoot/AliPhysics/O2 directories are mere Git repositories, you simply need to cd into them and checkout the Git version you want.

For instance, if you want to build AliPhysics against AliRoot v5-09-33, you would need to first move to the AliRoot directory and check the version out:

cd ~/alice/AliRoot
git fetch upstream --tags
git checkout v5-09-33


cd ~/alice/AliPhysics
git checkout master
git pull --rebase upstream master


and then build normally using the aliBuild command. You might want to build using different -z options as explained here in order to have different builds usable in parallel without duplicating your source code.

## 🧹 Delete obsolete builds

With frequent rebuilding of packages, obsolete builds can pile up and occupy a lot of precious disk space.

### Basic cleanup

The simplest way to get rid of obsolete builds is to let aliBuild do its best by running:

aliBuild clean


which can take the optional argument --aggressive-cleanup that deletes also source code of built dependency packages and downloaded .tar.gz archives.

In general, it's good practice to run aliBuild clean always after aliBuild build.

This might not be enough, as aliBuild will not delete any build directory pointed to by a symlink that has "latest" in its name, even when that build is not needed by any other package anymore. Manual intervention is therefore sometimes needed.

### Deep cleanup

If you want to keep only the latest builds of your development packages (and their dependencies), you can make aliBuild delete the rest with a little trick.

1. Delete symlinks to all builds:
find $ALIBUILD_WORK_DIR/$(aliBuild architecture)/ -mindepth 2 -maxdepth 2 -type l -delete
find $ALIBUILD_WORK_DIR/BUILD/ -mindepth 1 -maxdepth 1 -type l -delete  In case you specified the architecture manually (using the -a option with aliBuild build), you should replace $(aliBuild architecture) with your manually specified architecture.
2. Recreate symlinks to the latest builds of development packages (and their dependencies) by running aliBuild build for each development package.
3. Let aliBuild delete all the other builds by running aliBuild clean.