A dialog listing the problem items (exceptions) will pop up when you click the yellow CEL icon. The CEL will blink for fatal errors, such as the failure to spawn a new network namespace or failure to launch EMANE processes. The affected node is also highlighted so it is easy to find.
Node services have a new field named validation commands. These commands (if any) are invoked following the service startup commands to verify that the service has correctly started. The validation commands for existing services are currently defined with something like `pidof ospfd`, to check that a daemon is actually running. A non-zero return code from a validation command causes a CEL exception to be thrown.
The motivation for the CEL is to be more informative about underlying emulation problems. With previous versions of CORE, something may have gone terribly wrong, but the GUI continued happily along with no indication of issues. We're also cooking up some performance monitoring scripts that monitor the CPU, memory, and throughput used by nodes; future plans are to tie in performance alarms with this exception system.
