What is LCG software?
The LCG software stack is built by the CERN experimental physics department’s software group (EP-SFT) and includes a large number of packages that are used by all or many of the CERN experiments. Athena (but not AnalysisBase) is built on top of LCG. The LCG stack includes the event generators, Geant4, ROOT and many other essential packages. You can find a full list of packages, releases and versions here.
When to use LCG software directly?
If you aren’t using ATLAS software but need access to one of the LCG components, or a specific version of one of the packages, it can be convenient to set up an LCG release from CVMFS and then use the relevant software directly. In addition some of the LCG packages can’t be used in the ATLAS software environment - one example includes the Julia programming language. Again, many people may find that working against an LCG release may be the easiest way to use such software.
How to set up an LCG release
You must have a machine with a CVMFS installation. On such machines setting up LCG is as simple as
setupATLAS
lsetup "views <LCG_release> <arch-os-complier>"
where <LCG_release> is the desired LCG release and <arch-os-complier> specifies the architecture and compiler that the release was build for/with. For example:
lsetup "views LCG_106 x86_64-el9-gcc13-opt"
for x86 machines and
lsetup "views LCG_106 aarch64-el9-gcc13-opt"
for aarch64 (ARM). After this you can use any of the software in the stack that ships with the chosen release (LCG_106 in this case).
You can get a full list of the available releases and builds at this page.
Do not set up such a release in the same session as Athena or AnalysisBase as the environments may conflict. Do not set up LCG software in your login scripts, for the same reason.