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Chapter 21. Using early kdump to capture boot time crashes

You use the early kdump mechanism of the kdump service to capture the vmcore file during the early stages of the boot process. With the following information and the procedure, you can understand the early kdump mechanism, configuring, and checking the status of early kdump`.

21.1. What is early kdump

Kernel crashes during the booting phase occur when the kdump service is not yet started, and cannot facilitate capturing and saving the contents of the crashed kernel’s memory. Therefore, the vital information for troubleshooting is lost.

To address this problem, RHEL 8 introduced the early kdump feature as a part of the kdump service.

21.2. Enabling early kdump

The early kdump feature sets up the crash kernel and the initial RAM disk image (initramfs) to load early enough to capture the vmcore information for an early crash. This helps to eliminate the risk of losing information about the early boot kernel crashes.

Prerequisites

  • An active RHEL subscription.
  • A repository containing the kexec-tools package for your system CPU architecture
  • Fulfilled kdump configuration and targets requirements.

Procedure

  1. Verify that the kdump service is enabled and active: 

    # systemctl is-enabled kdump.service && systemctl is-active kdump.service enabled active

    If kdump is not enabled and running, set all required configurations and verify that kdump service is enabled.

  2. Rebuild the initramfs image of the booting kernel with the early kdump functionality: 

    # dracut -f --add earlykdump

  3. Add the rd.earlykdump kernel command line parameter: 

    # grubby --update-kernel=/boot/vmlinuz-$(uname -r) --args="rd.earlykdump"

  4. Reboot the system to reflect the changes 

    # reboot

Verification step

  • Verify that rd.earlykdump was successfully added and early kdump feature was enabled: 

    # cat /proc/cmdline
BOOT_IMAGE=(hd0,msdos1)/vmlinuz-4.18.0-187.el8.x86_64 root=/dev/mapper/rhel-root ro crashkernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet rd.earlykdump

# journalctl -x | grep early-kdump
Mar 20 15:44:41 redhat dracut-cmdline[304]: early-kdump is enabled.
Mar 20 15:44:42 redhat dracut-cmdline[304]: kexec: loaded early-kdump kernel

Additional resources