A look into what causes kernel panics and some utilities to help gain more information.

Working in a Linux environment, how often have you seen a kernel panic? When it happens, your system is left in a crippled state until you reboot it completely. And, even after you get your system back into a functional state, you're still left with the question: why? You may have no idea what happened or why it happened. Those questions can be answered though, and the following guide will help you root out the cause of some of the conditions that led to the original crash.

Figure 1. A Typical Kernel Panic

Let's start by looking at a set of utilities known as kexec and kdump. kexec allows you to boot into another kernel from an existing (and running) kernel, and kdump is a kexec-based crash-dumping mechanism for Linux.

Installing the Required Packages

First and foremost, your kernel should have the following components statically built in to its image:

CONFIG_RELOCATABLE=y
CONFIG_KEXEC=y
CONFIG_CRASH_DUMP=y
CONFIG_DEBUG_INFO=y
CONFIG_MAGIC_SYSRQ=y
CONFIG_PROC_VMCORE=y

You can find this in /boot/config-`uname -r`.

Make sure that your operating system is up to date with the latest-and-greatest package versions:

$ sudo apt update && sudo apt upgrade

Install the following packages (I'm currently using Debian, but the same should and will apply to Ubuntu):

$ sudo apt install gcc make binutils linux-headers-`uname -r`
 ↪kdump-tools crash `uname -r`-dbg

Note: Package names may vary across distributions.

During the installation, you will be prompted with questions to enable kexec to handle reboots (answer whatever you'd like, but I answered "no"; see Figure 2).

Figure 2. kexec Configuration Menu

And to enable kdump to run and load at system boot, answer "yes" (Figure 3).

Figure 3. kdump Configuration Menu

Configuring kdump

Open the /etc/default/kdump-tools file, and at the very top, you should see the following: