Kernel command line

Crashkernel size

The crashkernel size should be correctly set to avoid out of memory exception:

Red Hat supports crashkernel=auto
SUSE has a kdump calibrate command which can calculate the estimated crashkernel size

Both variants are not bullet-proof and might need manual tweaking.

Crashkernel syntax

crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]

For:

range=start-[end]: start is inclusive.; end is exclusive.

Use this to scale the crashkernel size if crashkernel=auto does not suit your needs. The @offset value must be greater or equal to your reserved memory size because the dump kernel is relocated before it runs.

Exclude unused devices

cio_ignore from s390-utils can be used to generate the kernel command line to exclude unused devices. This can help to reduce the memory consumption during the kdump boot process. You can append the result to the kernel command line.

$ cio_ignore -k -u
cio_ignore=all,!1234-123f,!1700

LUKS encrypted devices

Using memory-hard functions might require you to adjust the crashkernel size. For example, the default Aragon2 requires 1GB of extra memory to work correctly.

kdump config location

Red Hat:

/etc/sysconfig/kdump

SUSE:

/etc/sysconfig/kdump