Linux: Disable Kdump

July 10, 2025 Leave a comment

To disable Kdump, follow these steps:

1. Disable the kdump service:

# systemctl disable --now kdump.service

2. Check that the kdump service is inactive:

# systemctl status kdump.service

3. Remove kexec-tools package

# rpm -e kexec-tools

4. (Optional) Remove the crashkernel command-line parameter from the current kernel by running the following command:

# grubby --remove-args="crashkernel" --update-kernel=/boot/vmlinuz-$(uname -r)

Or set the desired value using grubby --update-kernel=/boot/vmlinuz-$(uname -r) --args="crashkernel=....” (Instead of dots, indicate your value).

ℹ️ One possible error that may occur when removing the kexec-tools package is that it might indicate that the package is not installed, even though it actually is. In this case, you can try rebuilding the RPM database and then rerunning the erase command.

# rpm --rebuilddb
# rpm -e kexec-tools

Filed under Linux, Oracle Enterprise Linux, OS Tagged with , , , , , ,

Linux: Enable Kdump

July 3, 2025 Leave a comment

Some systems may have Kernel crash dumps (kdump) disabled due to performance concerns. When encountering a kernel panic and contacting RHEL support, they might request a kdump. You are advised to enable kdump and either wait for the incident to occur or manually trigger it to observe the kernel panic. Kdump must be enabled in order for the incident to generate the dump files.

1. If kernel-tools package is removed from the system, install it:

# yum install kexec-tools -y

2. To reserve memory for Crashkernel, add the crashkernel option to the current kernel:

# grubby --update-kernel=/boot/vmlinuz-$(uname -r) --args="crashkernel=1G"

3. Reboot the System

# reboot

4. Enable and start Kdump service

# systemctl enable --now kdump.service

5. Verify Kdump is running

# systemctl status kdump.service

● kdump.service - Crash recovery kernel arming
   Loaded: loaded (/usr/lib/systemd/system/kdump.service; enabled; vendor prese>
   Active: active (exited) since Tue 2025-06-24 20:29:58 UTC; 7min ago
 Main PID: 1169 (code=exited, status=0/SUCCESS)
    Tasks: 0 (limit: 196884)
   Memory: 0B
   CGroup: /system.slice/kdump.service

⚠️ Testing: Trigger a Kernel Panic

Please note that I will show you a command that can trigger a kernel panic. This will allow you to check if a dump is generated. This is meant for testing purposes only and should not be executed on a production system during working hours. 🙂

Are you sure you want to cause a kernel panic right now? – If yes, then here is the command:

# echo c > /proc/sysrq-trigger

At this point, the node/VM has crashed and rebooted. When you relog in, you can check /var/crash/ directory to see if crash data was generated.

# ll /var/crash/
...
drwxr-xr-x 2 root root 67 Jun 24 20:15 127.0.0.1-2025-06-24-20:15:51

# cd /var/crash/
# ll
..
drwxr-xr-x 2 root root 67 Jun 24 20:15 127.0.0.1-2025-06-24-20:15:51

# cd 127.0.0.1-2025-06-24-20\:15\:51/

# ll
...
-rw------- 1 root root     45904 Jun 24 20:15 kexec-dmesg.log
-rw------- 1 root root 242941092 Jun 24 20:15 vmcore
-rw------- 1 root root     43877 Jun 24 20:15 vmcore-dmesg.txt
⚠️ Be sure to monitor disk space in /var/crash, as vmcore files can be large.

Filed under Linux, Oracle Enterprise Linux, OS Tagged with , , , , , , ,