The threshold for statically assigned UID/GID numbers (defined by the setup package in the
/usr/share/doc/setup-*/uidgid file) has increased from 100 (in Red Hat Enterprise Linux 3, 4, and 5) to 200 in Red Hat Enterprise Linux 6. This change can affect systems that have 100-200 dynamically or statically assigned UID/GIDs, and cause failure in the installation and running of some applications.
Dynamic UID/GID allocation now ranges from 499 downward in Red Hat Enterprise Linux 6. For static system user creation without reservations enforced by the setup package, it is recommended to use the UID/GID area of 300 and above.