Hi Norbert, If ifeffit and gifeffit work OK, then the fortran and c compilers are OK, and so the problem is almost certainly specific to the perl module. So I'm sorry you rebuilt gcc. I'll update Fortran.Notes to explain that this is really an issue with now very old linux systems that should be updated anyway. For the record, I have not had problems with gcc 2.95.3 or gcc 2.96 on RedHat 7.* linuxes, and have not needed to rebuilding compilers to get ifeffit to run. Please don't interpret that as 'SusE is broken, install RedHat'!!! For one thing, I believe Bruce uses SuSE with some success. ;) Anyway, back to diagnosing your problem: After a 'perl Makefile.PL ; make install ', could you please let us know: Q1. Does tkatoms work? If so, I think this implies that C extensions _can_ be built and run on your machine. Q2. What does perl -e 'use Ifeffit;' say? Q3. If this says anything, then what is in Makefile.PL? Since other the python installation worked, what do /usr/local/share/ifeffit/config/Config.mak /usr/local/share/ifeffit/config/site_install.py look like? These should have equivalent information, though formatted differently. One thing to look for the 'LIBS' line in Makefile.PL has '-lf2c' or '-lg2c' *before* the '-L/usr/lib/gcc/...' line. If so, it might be that moving the '-lg2c' to *after* the 'L/...' bit will help. --Matt