I'm building an RPM of a DNS server called NSD on CentOS 4.4. I'm going to be using it for some heavy-duty DNS traffic, so I want to minimise its dependencies on external libraries. I have therefore attempted to link it statically.

The package does build, and even runs fine. However, during the build process, gcc emits warnings like these:

nsd.o(.text+0xfba): In function `main': : warning: Using 'getpwnam' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking

My understanding of this is because glibc uses dlopen to load other shared objects at runtime. I therefore need a Requires: line in the RPM which requires glibc-2.3.4-2.36, or whatever version I used to build nsd.

Now, what I want to ask is: if the version of glibc is upgraded to say 2.3.4-2.48, what happens? What do the numbers after the version number mean (2.48) and what effect will that have on packages which are statically linked against glibc?

Another question which has occured to me is this: NSD also uses other libraries, such as openssl. Is there any way to know if any of the openssl libraries use dlopen to load in other shared objects? If they do, then it introduces dependencies that I may not be aware of, and doing static linking wouldn't be as beneficial as I first thought it would be.

Comments from experienced developers will be most appreciated.