You should be able to easily build your own ROOT “in-place”:
[root.cern.ch/phpBB3/viewtopic.p … 931#p76931](Missing Canvas
[root.cern.ch/phpBB3/viewtopic.p … 797#p78797](Trouble Installing
[root.cern.ch/phpBB3/viewtopic.p … 839#p78839](Problem with png of divided canvas in 5-34/19 on Mac
Just add “–enable-pythia8 --with-pythia8-incdir=${PYTHIA8}/include --with-pythia8-libdir=${PYTHIA8}/lib” to the configure flags.
Also, before building your new ROOT version, make sure that nothing in your environment variables (i.e. “ROOTSYS”, “PATH”, “LD_LIBRARY_PATH”) points to another existing version of ROOT. Try:
echo ${ROOTSYS}
echo ${PATH}
echo ${LD_LIBRARY_PATH}
which root
type root
which rootcint
type rootcint
and see if there’s anything related to another ROOT version (if yes, you need to make sure that it’s not “seen”).