when running systematics, trying to download pdf that is already installed

Hi,

The error is raised by LHAPDF,
Not sure why it crashed after notifying that it has it already present:
> 16:31:00 PDF already installed: NNPDF23_lo_as_0130_qed (use --upgrade to force install)

But indeed we should not request lhapdf to try to download it in this case.
This is due to the fact that we consider only the first path in the LHAPDF_DATA_PATH
with a valid pdfsets.index.

> It is located at $(lhapdf-config --datadir), the location is also part (the second part) of $LHAPDF_DATA_PATH.

Madgraph only consider the first part since the first part contains pdfsets.index
If it does not find it there, it will ask lhapdf to re-download it.
I will correct that issue in the next version of MG5aMC.

Cheers,

Olivier

> On 26 Mar 2020, at 20:27, Hannes <email address hidden> wrote:
>
> New question #689522 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/689522
>
> Hi,
>
> we have an issue that is non-critical but a bit confusing to people generating with MadGraph in ATLAS, see the error message at the bottom. Systematics calculation runs fine, with arbitrary pdfs, despite the message.
>
> It looks like MadGraph fails in different ways trying to download pdf sets. One of them is obviously because lhapdf is installed in a read only dir. The thing is, there should be no need to download the pdf in the first place.
>
> It is located at $(lhapdf-config --datadir), the location is also part (the second part) of $LHAPDF_DATA_PATH.
>
> How can this crash be avoided?
>
> Cheers,
> Hannes
>
> 16:30:49 INFO: Running Systematics computation
> 16:30:50 INFO: Trying to download NNPDF23_lo_as_0130_qed
> 16:31:00 PDF already installed: NNPDF23_lo_as_0130_qed (use --upgrade to force install)
> 16:31:00 /cvmfs/atlas.cern.ch/repo/sw/software/21.6/sw/lcg/releases/LCG_88/MCGenerators/lhapdf/6.2.3/x86_64-slc6-gcc62-opt/share/LHAPDF/NNPDF23_lo_as_0130_qed.tar.gz: Read-only file system
> 16:31:00 tar (child): NNPDF23_lo_as_0130_qed.tar.gz: Cannot open: No such file or directory
> 16:31:00 tar (child): Error is not recoverable: exiting now
> 16:31:00 tar: Child returned status 2
> 16:31:00 tar: Error is not recoverable: exiting now
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Can you try this:
https://bazaar.launchpad.net/~mg5core1/mg5amcnlo/2.7.3/revision/289?start_revid=289

This should fix the issue if I'm correct.

Cheers,

Olivier

Hello, I also get the same issue with Madgraph 3.2.0. Madgraph only considers the first path in LHAPDF_DATA_PATH and attempts to re-download the pdf if not found there.

Interestingly, even after the:
> Error is not recoverable: exiting now
message, event generation continues and seems to proceed as expected with the correct pdf.

Claudio