Chapter 18. Enabling kdump

Procedure

1. Add the crashkernel= command-line parameter to all installed kernels:

   # grubby --update-kernel=ALL --args="crashkernel=xxM"

   xxM is the required memory in megabytes.

2. In terms of UKI, add the crashkernel= command-line parameter to all installed UKIs by copying an add-on associated with the required argument from /lib/modules/$(uname -r)/vmlinuz-virt.efi.extra.d/ to /boot/efi/loader/addons/.

3. Reboot the system:

   # reboot

4. Enable the kdump service:

   # systemctl enable --now kdump.service

Procedure

1. List the kernels installed on the machine:

   # ls -a /boot/vmlinuz-*

   /boot/vmlinuz-0-rescue-2930657cd0dc43c2b75db480e5e5b4a9
   /boot/vmlinuz-6.12.0-55.9.1.el10_0.x86_64
   /boot/vmlinuz-6.12.0-55.9.1.el10_0.x86_64

2. Add a specific kdump kernel to the system’s Grand Unified Boot Loader (GRUB) configuration:

   For example:

   # grubby --update-kernel=vmlinuz-6.12.0-55.9.1.el10_0.x86_64 --args="crashkernel=xxM"

   xxM is the required memory reserve in megabytes.

3. In terms of UKI, add the crashkernel= command-line parameter to a specific UKI by copying an add-on associated with the required argument from /lib/modules/$(uname -r)/vmlinuz-virt.efi.extra.d/ to /boot/efi/EFI/Linux/<machine-id>-<kernel-version>.efi.extra.d/.

4. Enable the kdump service:

   # systemctl enable --now kdump.service

Procedure

1. To stop the kdump service in the current session:

   # systemctl stop kdump.service

2. To disable the kdump service:

   # systemctl disable kdump.service

   Warning

   You must set kptr_restrict=1 as default. When kptr_restrict is set to (1) as default, the kdumpctl service loads the crash kernel regardless of whether the Kernel Address Space Layout (KASLR) is enabled.

   If kptr_restrict is not set to 1 and KASLR is enabled, the contents of /proc/kore file are generated as all zeros. The kdumpctl service fails to access the /proc/kcore file and load the crash kernel. The kexec-kdump-howto.txt file displays a warning message, which suggest you to set kptr_restrict=1. Verify for the following in the sysctl.conf file to ensure that kdumpctl service loads the crash kernel:

   • Kernel kptr_restrict=1 in the sysctl.conf file.