The present invention, belonging to the field of computer technologies, relates to a method and apparatus for upgrading an operating system. The method comprises: upgrading an operating system; monitoring whether an abnormal signal broadcast by a kernel of the operating system exists during the upgrade process, the abnormal signal being generated when the kernel detects that access of a process address encounters a failure; and processing the abnormal signal when the abnormal signal is monitored. According to the present invention, the problem that anomaly is generated during the upgrade of the operating system via the Recovery service, and cannot be handled can be solved, which achieves the effect of processing the anomaly that is generated during the upgrade. In this way, success rate of the upgrade is improved.