A system includes a baseboard management controller (BMC), capable of online update of the BMC without shutting down any services. The BMC includes a processor, a volatile memory configured to perform multiple service instances, and a non-volatile memory storing a computer executable code and a root file system. The root file system includes multiple service modules as origin of the service instances. The computer executable code, when executed at the processor, is configured to: receive an update command and perform an update process based on the update command. The update process includes: copying the root file system from the non-volatile memory to the volatile memory; switching the origin of the service instances to the copy of the root file system; receiving an update root file system code; and writing the update root file system code to the non-volatile memory to obtain an updated root file system.