Comment 1 for bug 1650664

First of all, I would like to stress that this "new set of programs" is much more involved than previously considered ones for automatic installation and with many issues out of MG5_aMC control which should be addressed directly by their corresponding authors.
This automatic installation option is a difficult enterprise that requires tedious development to make as stable as possible on many system, and for which little to no credit is awarded.
So I thank you in advance for your understanding of the issues faced, especially in the early stages of the release.
That being said, I appreciate your feedback which will hopefully help improving the stability of such automated installations within MG5aMC.

Regarding your errors:

a)

Error: main91 requires ROOT
Error: main92 requires ROOT
 Finished PYTHIA8 installation

Pythia8 compiles by default all example drivers, and skips the ones requiring roots (if not enabled, the MG5_aMC installer automatically detects whether it is available or not based on your environment variables). It does so with this unnecessarily scary message, but I believe that in this case Pythia8 installation was successful.

b)

Detected 'mg5amc_py8_interface' missing dependency: 'pythia8'. Will install it now.

MG5aMC looks for pythia8 by scanning your LIBRARY_PATH and/or LD_LIBRARY_PATH.
In the case of pythia8 it will look for the existence of the library 'libpythia8.(a|so|dylib)' in these paths.

However, if the pythia8 path is already specified in MG5_aMC option 'pythia8_path' (please double check that before running 'install mg5amc_py8_interface' by running the command 'display pythia8_path' in the interactive interface) then it should force its use, and I indeed don't understand why it says:

Detected 'mg5amc_py8_interface' missing dependency: 'pythia8'. Will install it now.

In my case the pythia8_path option is set to:

pythia8_path : /Users/valentin/Documents/Work/MG5/HEPTools/pythia8 (user set)

Please let me know if indeed pythia8_path was correctly set, and if so, I'll look into this further.

c) The same comment as for item b) above holds true for lhapdf6 as well, in which case MG5aMC will look for the library 'libLHAPDF.(a|so|dylib)' if not already specified in the MG5aMC option 'lhapdf' where the path to the executable 'lhapdf-config' should be specified, if not already available from your system-wide PATH variable.

d) When installing LHAPDF, the error:

PDF.cc:62:1: internal compiler error: in insn_default_length, at config/i386/i386.md:2072

Seems clearly related to an issue in the compiler used. What is your compiler suite (apparently cc1plus , but what version) used when encountering this issue? Have you set anything in the MG5aMC option 'cpp_compiler' (you shouldn't need to).

Notice that you can force pythia8 *not* to link against lhapdf by adding the following option to its installation from MG5aMC:

MG5_aMC> install pythia8 --with_lhapdf5=OFF --with_lhapdf6=OFF --logging=DEBUG --keep_source

since lhapdf is not mandatory for Pythia8 (the last two options I wrote are optional and just there for better monitoring).
Just to be safe, when doing that also make sure that the lhapdf option of MG5_aMC is disabled by specifying the option 'lhapdf' in <MG5_install_dir>/input/mg5_configuration.txt to be an empty string. (uncomment the line if commented too) or alternatively, make sure 'lhapdf-config' is not available system-wide (that is if you type 'which lhadf-config', it returns nothing.

e) When installing MG5aMC_PY8_interface, the error clearly seems to come from the HEPMC library that was detected on your system and that MG5aMC therefore tries to link to.
Could you then try to first install HEPMC with MG5aMC using

MG5_aMC> install hepmc

And then again re-install pythia8 and the MG5aMC_PY8_interface? MG5aMC will always prefer versions of the tools it locally installed itself over those detected system-wide, so the newly install hepmc will be used instead.