When the JNI-based users-group mapping is enabled, the process/command will fail if the native library, libhadoop.so, cannot be found. This mostly happens at client-side where users may use hadoop programatically. Instead of failing, falling back to the shell-based implementation will be desirable. Depending on how cluster is configured, use of the native netgroup mapping cannot be subsituted by the shell-based default. For this reason, this behavior must be configurable with the default being "disabled".