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Chapter 21. Using early kdump to capture boot time crashes

Early kdump is a feature of the kdump mechanism to capture the vmcore file if a system or kernel crash occurs during the early phases of the boot process before the system services start. Early kdump loads the crash kernel and the crash kernel’s initramfs in the memory much earlier.

21.1. What is early kdump

A kernel crash can sometimes occur during the early boot phase before the kdump service starts and is able to capture and save the contents of the crashed kernel memory. Therefore, crucial information related to the crash, which is important for troubleshooting, is lost. To address this problem, you can use the early kdump feature, which is 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. For more information see, Supported kdump configurations and targets.

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