Power-on self-test (POST) is a group of PROM-based tests that run when the server is powered on or reset. POST checks the basic integrity of the critical hardware components in the server (CMP, memory, and I/O subsystem).
POST tests critical hardware components to verify functionality before the system boots and accesses software. If POST detects a faulty component, the component is disabled automatically, preventing faulty hardware from potentially harming any software. If the system is capable of running without the disabled component, the system will boot when POST is complete. For example, if one of the processor cores is deemed faulty by POST, the core will be disabled. The system will boot and run using the remaining cores.
You can use POST as an initial diagnostic tool for the system hardware. In this case, configure POST to run in maximum mode (diag_mode=service, setkeyswitch=diag, diag_level=max) for thorough test coverage and verbose output.