Obtaining a dump with limited size

The mem kernel parameter can make Linux use less memory than is available to it. A dump of such a Linux system does not need to include the unused memory. You can use the zipl command with the size option to limit the amount of memory that is dumped.

About this task

The size option is available for all zipl based dumps except SCSI: DASD and tape in command-line mode or in configuration-file mode. The size option is appended to the dump device specification with a comma as separator.

The value is a decimal number that can optionally be suffixed with K for kilobytes, M for megabytes, or G for gigabytes. Values that are specified in byte or kilobyte are rounded to the next megabyte boundary.

Be sure not to make the dump size smaller than the amount of memory that is actually used by the system to be dumped. Limiting the dump size to less than the amount of used memory results in an incomplete dump.

Example

The following command, entered in a Linux shell, prepares a DASD dump device for a dump that is limited to 100 MB:

# zipl -d /dev/dasdc1,100M
Setting dump size limit to 100MB
Dump target: partition '/dev/dasdc1' with a size of 7043 MB.
Warning: All information on partition '/dev/dasdc1' will be lost!
Do you want to continue creating a dump partition (y/n)?y
Done.

After IPL of the dump device, you can see output from the dump tool on the z/VM® console as the dump is created:

00:
00: CP I 63AD
01: HCPGSP2630I The virtual machine is placed in CP mode due to a SIGP stop
    and store status from CPU 00.
02: HCPGSP2630I The virtual machine is placed in CP mode due to a SIGP stop
    and store status from CPU 00.
00: zIPL v1.15.0-0.132.4 dump tool (64 bit)
00: Dumping 64 bit OS
00:
00: 00000012 / 00000100 MB
00: 00000025 / 00000100 MB
00: 00000037 / 00000100 MB
00: 00000050 / 00000100 MB
00: 00000062 / 00000100 MB
00: 00000075 / 00000100 MB
00: 00000087 / 00000100 MB
00: 00000100 / 00000100 MB
00: Dump successful
00: HCPGIR450W CP entered; disabled wait PSW 00020000 80000000 00000000 00000000