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Chapter 16. Enabling kdump

By using the procedure, you can enable or disable the kdump service for all installed kernels or for a specific kernel.

16.1. Enabling kdump for all installed kernels

You can enable and start the kdump service for all kernels installed on the machine.

Prerequisites

  • Administrator privileges

Procedure

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

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

  2. Enable the kdump service. 

    # systemctl enable --now kdump.service

Verification

  • Check that the kdump service is running: 

    # systemctl status kdump.service

○ kdump.service - Crash recovery kernel arming
     Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled; vendor preset: disabled)
     Active: active (live)

16.2. Enabling kdump for a specific installed kernel

You can enable the kdump service for a specific kernel on the machine.

Prerequisites

  • Administrator privileges

Procedure

  1. List the kernels installed on the machine. 

    # ls -a /boot/vmlinuz-*
/boot/vmlinuz-0-rescue-2930657cd0dc43c2b75db480e5e5b4a9 /boot/vmlinuz-4.18.0-330.el8.x86_64 /boot/vmlinuz-4.18.0-330.rt7.111.el8.x86_64

  2. Add a specific kdump kernel to the system’s Grand Unified Bootloader (GRUB) configuration file.

    For example: 

    # grubby --update-kernel=vmlinuz-4.18.0-330.el8.x86_64 --args="crashkernel=auto"

  3. Enable the kdump service. 

    # systemctl enable --now kdump.service

Verification

  • Check that the kdump service is running: 

    # systemctl status kdump.service

○ kdump.service - Crash recovery kernel arming
     Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled; vendor preset: disabled)
     Active: active (live)

16.3. Disabling the kdump service

To disable the kdump service at boot time, follow the procedure below.

Prerequisites

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

It is recommended to set kptr_restrict=1. In that case, the kdumpctl service loads the crash kernel regardless of Kernel Address Space Layout (KASLR) being enabled or not.

Troubleshooting step

When kptr_restrict is not set to (1), and if KASLR is enabled, the contents of /proc/kcore file are generated as all zeros. Consequently, the kdumpctl service fails to access the /proc/kcore and load the crash kernel.

To work around this problem, the /usr/share/doc/kexec-tools/kexec-kdump-howto.txt file displays a warning message, which recommends the kptr_restrict=1 setting.

To ensure that kdumpctl service loads the crash kernel, verify that kernel.kptr_restrict = 1 is listed in the sysctl.conf file.

Additional resources