crashkernel=auto parameter is deprecated in RHEL9

Environment

• Red Hat Enterprise Linux 9
• kdump

Issue

• New kdump kernel fails to boot
• kdump fails to generate vmcore file in newer kernel
• crashkernel=auto does not work

Resolution

Run below command to set crashkernel parameter:

# kdumpctl reset-crashkernel

Root Cause

• crashkernel=auto is dropped and kernel package now includes a crashkernel.conf indicating the default crashkernel value of a kernel release.
  kexec-tools should provide new commands and scripts to update kernel crashkernel value based on this.

Diagnostic Steps

Steps to reproduce:

1. Set crashkernel=auto in /etc/default/grub:

# vi /etc/default/grub

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto resume=/dev/mapper/rhel_dhcp131--89-swap rd.lvm.lv=rhel_dhcp131-89/root rd.lvm.lv=rhel_dhcp131-89/swap rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true

2. Rebuild the file:

# grub2-mkconfig -o /boot/grub2/grub.cfg

3. It appends crashkernel=auto by default:

# grubby --info DEFAULT
index=0
kernel="/boot/vmlinuz-5.14.0-39.el9.x86_64"
args="ro resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet crashkernel=auto"
root="/dev/mapper/rhel-root"
initrd="/boot/initramfs-5.14.0-39.el9.x86_64.img"
title="Red Hat Enterprise Linux (5.14.0-39.el9.x86_64) 9.0 (Plow)"
id="6b56f578b88e45aeaf1502729b134106-5.14.0-39.el9.x86_64"

4. Reboot the system for crashkernel to take effect.
5. Check the current reserved memory size:

# kdumpctl showmem
kdump: Reserved 0MB memory for crash kernel  <<--- observe 0 MB

6. Test the kdump by manually crashing the machine:

# echo c > /proc/sysrq-trigger

Fails to boot, No vmcore. System reset needed

RESET

1. Set the crashkernel using reset-crashkernel sub-command:

# kdumpctl reset-crashkernel

2. It appends crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M by default:

# grubby --info DEFAULT
index=0
kernel="/boot/vmlinuz-5.14.0-39.el9.x86_64"
args="ro resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M"
root="/dev/mapper/rhel-root"
initrd="/boot/initramfs-5.14.0-39.el9.x86_64.img"
title="Red Hat Enterprise Linux (5.14.0-39.el9.x86_64) 9.0 (Plow)"
id="6b56f578b88e45aeaf1502729b134106-5.14.0-39.el9.x86_64"

3. Reboot the system for crashkernel to take effect
4. crashkernel reserves 192MB:

# kdumpctl showmem
kdump: Reserved 192MB memory for crash kernel

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