If you are running CentOS on a linode and, after doing a "yum update", bind/host/nslookup starts segfaulting, simply move /lib/tls out of the way to disable NPTL. The glibc implementation is recent CentOS updates conflicts with Linode's NPTL kernels (not sure how, but I know it does). Deleting and/or moving /lib/tls out of the way solves this. This will actually affect several programs on the system, but the bind suite is the most noticable.