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update kexec-kdump-howto

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1. yum is deprecated so use dnf instead
2. use the "kdumpctl reset-crashkernel" API
3. ask the users to refer to crashkernel-howto.txt for setting custom
   crashkernel value
4. fix a typo

Philipp Rudo <prudo@redhat.com>

Signed-off-by: Coiby Xu <coxu@redhat.com>
This commit is contained in:
Coiby Xu 2022-03-01 17:30:50 +08:00
parent 683ff87821
commit 1e7df3e1f3
1 changed files with 20 additions and 12 deletions
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kexec-kdump-howto.txt
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@ -44,7 +44,7 @@ ia64 and ppc64.
If you're reading this document, you should already have kexec-tools
installed. If not, you install it via the following command:
# yum install kexec-tools
# dnf install kexec-tools
Now load a kernel with kexec:
@ -66,23 +66,31 @@ How to configure kdump
Again, we assume if you're reading this document, you should already have
kexec-tools installed. If not, you install it via the following command:
# yum install kexec-tools
# dnf install kexec-tools
To be able to do much of anything interesting in the way of debug analysis,
you'll also need to install the kernel-debuginfo package, of the same arch
as your running kernel, and the crash utility:
# yum --enablerepo=\*debuginfo install kernel-debuginfo.$(uname -m) crash
# dnf --enablerepo=\*debuginfo install kernel-debuginfo.$(uname -m) crash
Next up, we need to modify some boot parameters to reserve a chunk of memory for
the capture kernel. With the help of grubby, it's very easy to append
"crashkernel=128M" to the end of your kernel boot parameters. Note that the X
values are such that X = the amount of memory to reserve for the capture kernel.
And based on arch and system configuration, one might require more than 128M to
be reserved for kdump. One need to experiment and test kdump, if 128M is not
sufficient, try reserving more memory.
Next up, we need to reserve a chunk of memory for the capture kernel. To use
the default crashkernel value, you can kdumpctl:
# grubby --args="crashkernel=128M" --update-kernel=/boot/vmlinuz-`uname -r`
# kdumpctl reset-crashkernel --kernel=/boot/vmlinuz-`uname -r`
If the default value does not work for your setup you can use
# grubby --args="crashkernel=256M" --update-kernel=/boot/vmlinuz-`uname -r`
to specify a larger value, in this case 256M. You need to experiment to
find the best value that works for your setup. To begin with
# kdumpctl estimate
gives you an estimation for the crashkernel value based on the currently
running kernel. For more details, please refer to the "Estimate crashkernel"
section in /usr/share/doc/kexec-tools/crashkernel-howto.txt.
Note that there is an alternative form in which to specify a crashkernel
memory reservation, in the event that more control is needed over the size and
@ -135,7 +143,7 @@ in /var/crash/<YYYY-MM-DD-HH:MM>/vmcore), then the system rebooted back into
your normal kernel.
Once back to your normal kernel, you can use the previously installed crash
kernel in conjunction with the previously installed kernel-debuginfo to
utility in conjunction with the previously installed kernel-debuginfo to
perform postmortem analysis:
# crash /usr/lib/debug/lib/modules/2.6.17-1.2621.el5/vmlinux