Chapter 17. Enabling kdump
For your RHEL 8 systems, you can configure enabling or disabling the kdump functionality on a specific kernel or on all installed kernels. However, you must routinely test the kdump functionality and validate its working status.
17.1. Enabling kdump for all installed kernels
The kdump service starts by enabling kdump.service after the kexec tool is installed. You can enable and start the kdump service for all kernels installed on the machine.
Prerequisites
- You have administrator privileges.
Procedure
Add the
crashkernel=command-line parameter to all installed kernels:# grubby --update-kernel=ALL --args="crashkernel=xxM"
xxMis the required memory in megabytes.Enable the
kdumpservice:# systemctl enable --now kdump.service
Verification
Check that the
kdumpservice 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)
17.2. Enabling kdump for a specific installed kernel
You can enable the kdump service for a specific kernel on the machine.
Prerequisites
- You have administrator privileges.
Procedure
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_64Add a specific
kdumpkernel to the system’s Grand Unified Bootloader (GRUB) configuration.For example:
# grubby --update-kernel=vmlinuz-4.18.0-330.el8.x86_64 --args="crashkernel=xxM"xxMis the required memory reserve in megabytes.Enable the
kdumpservice.# systemctl enable --now kdump.service
Verification
Check that the
kdumpservice 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)
17.3. Disabling the kdump service
You can stop the kdump.service and disable the service from starting on your RHEL 8 systems.
Prerequisites
-
Fulfilled requirements for
kdumpconfigurations and targets. For details, see Supported kdump configurations and targets. -
All configurations for installing
kdumpare set up according to your needs. For details, see Installing kdump.
Procedure
To stop the
kdumpservice in the current session:# systemctl stop kdump.service
To disable the
kdumpservice:# systemctl disable kdump.service
It is recommended to 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 recommends 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=1in thesysctl.conffile.
Additional resources
