Here is a recent answer to a question from a customer with the 2.3.4 C libraries that will not work with UnForm version 9.0. UnForm v9.0 requires at least 2.5 C libraries.
The 2.3.4 libraries are many years old, and the new runtime version UnForm 9 uses is not compatible with them. The ultimate test is to install a demo and see if it can be activated and started, but most likely that will fail.
We do not recommend attempting to update the C libraries, as those libraries are dependencies for much of Linux itself. Instead, we would recommend installing Unform on a newer Linux or Windows system, or even OS/X. The UnForm Linux/Unix client is still Perl-based and will run on a much wider range of systems.
To see what C library version your system has, use this command: ldd --version
Note there is sometimes confusion over the version naming convention used by libc. Version 2.5 is lower than a version 2.12, so a 2.12 system is fine. Think of 2.5 as 2.05, if that helps.
Here is a link to version history for the Linux C libraries for reference:
http://en.wikipedia.org/wiki/GNU_C_Library#Version_history