I understand the origin of the breakage of InsightII by Fedora Core 5 a little better now. It appears that the InsightII 2005 scripts were automatically setting... setenv LD_ASSUME_KERNEL 2.4.9 which Fedora Core 4 tolerates. Under glibc 2.4 of FC5, this causes the error... ls: error while loading shared libraries: librt.so.1: cannot open shared object file: No such file or directory rendering all binaries unusable. However if I don't set the LD_ASSUME_KERNEL environmental I get the error... /usr/accelrys/I2005/Linux_2_Intel_32/biosym_exe/insightII: relocation error: /usr/accelrys/I2005/Linux_2_Intel_32/biosymso/libcblib.so: symbol errno, version GLIBC_2.0 not defined in file libc.so.6 with link time reference Anyone know what LD_ASSUME_KERNEL settings are valid in glibc 2.4? Jack