A dump information acquiring method and a system recovery method for a computer system using a virtual memory, the methods being used when fault occurs in the computer system. The computer system has a plurality of external storage units used as a paging device unit for holding the contents of the virtual memory to be paged out from a main memory. During the normal operation, an external storage unit selected from the plurality of external storage units is used as the paging device unit. When fault occurs, a program for acquiring dump information operates to output the contents of the main storage at the time of the fault occurrence to a dump file. The identifier of the external storage unit set to definition information for defining the external storage unit used as the paging device unit is changed from the identifier of the external storage unit used as the page device unit to the identifier of another external storage unit. Thereafter, the computer system is restarted. The contents of the virtual memory held in the paging device unit at the time of the fault occurrence are output to the dump file by a program executed in a background of a job process of the current computer system or by a program executed by another computer system.