Hi, Sergio, Sergio Belkin wrote: > > I have a project that is a library that links against libresolv, > It works fine on recent distros: Ubuntu 10.x Fedora 13, Mandriva > 2010.1 but on Centos 5.x I get the following errors I'd assume that your undefined references were added in later versions of glibc. Remember that Fedora 13, for example, has more recent libraries, in some cases, with enhancements to the ones in CentOS. CentOS 5/RHEL 5 are based on FC 6 or so. With these, you get stability, but not the newest releases of some libraries. mark "and you don't usually need to debug the o/s"