Dangerous symlink on gridpack
The symlink created in https://gitlab.cern.ch/lhcb/Gauss/-/blob/master/Gen/LbMadgraph/src/component/MadgraphProduction.cpp#L99 (and also here https://gitlab.cern.ch/lhcb-datapkg/Gen/MadgraphData/-/blob/master/cmt/gridpack.sh#L93) exposes the directory hosting the PDFs (under the environment variable $LHAPDF_DATA_PATH
) to the internal Madgraph workspace. Then, the following lines are executed by Madgraph during runtime:
https://github.com/mg5amcnlo/mg5amcnlo/blob/main/madgraph/interface/common_run_interface.py#L4461
This snippet basically tries to remove whatever is inside PDFsets
: in our case whatever $LHAPDF_DATA_PATH
points to. In production cases this should be a cvmfs folder which is HOPEFULLY write protected. If not, all the pdfs get removed.
In particular, when testing a pdf locally if it is not properly write protected it will get erased.
I suggest to, instead of creating a symbolic link, to go for a readonly solution, but I'm not sure how to properly do it.