I've got different versions of the boost libraries installed on my system: one is installed system wide in /usr/lib64, while other versions are installed in /cvos/shared/apps/boost/gcc-4.[123]/1.35.0, compiled with the respective different versions of gcc. When I want to use one of the custom built libraries, I set the CPATH, LIBRARY_PATH and LD_LIBRARY_PATH variables to the respective include files and libraries. For the gcc 4.1 one, this works correctly: $ g++ -o test test.cpp -lboost_regex $ ldd test | grep boost libboost_regex.so.1.35.0 => /cvos/shared/apps/boost/ gcc-4.1/1.35.0/lib/libboost_regex.so.1.35.0 (0x00007f2352ad1000) And without the environment vars set, it links against the one in /usr/ lib64: libboost_regex.so.2 => /usr/lib64/libboost_regex.so.2 (0x00007fb000918000) However when I do exactly the same with gcc 4.2 and gcc 4.3, it always links against the libboost_regex.so.2 on in /usr/lib64 and not against the libboost_regex.so.1.35.0 in /cvos/shared/apps/boost/gcc-4.[23]/1.35.0/ lib, even though the LIBRARY_PATH and LD_LIBRARY_PATH variables have this directory set as first. The versions used are gcc 4.1.2 20070626 (Red Hat 4.1.2-14), stock gcc 4.2.4 and stock gcc 4.3.1. Has this behaviour changed in gcc 4.2, or is it something RH specific which makes that it works with my gcc 4.1? -- Frederik