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my super-extensive mother-of-all Linux topics book is not going to be Linux Kernel Crash Book is pages, lovely screenshots and tons of excellent. A book on Linux kernel crash analysis intended for system administrators and professionals dabbling in the kernel. However, Linux enthusiasts. How to debug a kernel crash – and other tricks. Who am I. ○ Name: Jesper Dangaard Brouer. – Linux Kernel Developer at Red Hat.

Linux Kernel Crash Book

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A first aid guide for Linux system and network administrators, this free book provides quick solutions to a variety of Linux system problems. It discusses in detail. Linux Kernel Crash Book by Igor Ljubuncic - free book at E-Books Directory. You can download the book or read it online. It is made freely available by its author. “Linux Kernel Crash Book”, by Igor Ljubuncic, starts with crash tools via collection all the way to analysis, plus some extras and general tips.

For systems and network administrators and technical support engineers responsible for maintaining Linux computer systems and networks. A first aid guide for Linux system and network administrators, this book provides quick solutions to a variety of Linux system problems.

It discusses in detail Linux system panics, crashes and hangs, their causes, what to do when they occur, how to collect information about them, how to analyze that information, and how to get the problem resolved. While you may not find immediate use to the contents presented in this book, the general knowledge and problem solving methods and tools you find here should serve you universally.

Come the day, come the opportunity, you will find this book of value. Book Site.

Click here for details. Book Description For systems and network administrators and technical support engineers responsible for maintaining Linux computer systems and networks.

site Related Book Categories: All Categories. Recent Books. IT Research Library. Jump to navigation. Penguin , Boot. Modified by Opensource.

Join the 85, open source advocates who receive our giveaway alerts and article roundups. Kdump is a way to acquire a crashed Linux kernel dump, but finding documents that explain its usage and internals can be challenging. Kexec is a Linux kernel-to-kernel boot loader that helps to boot the second kernel from the context of first kernel. Kexec shuts down the first kernel, bypasses the BIOS or firmware stage, and jumps to second kernel.

How to use kdump for Linux Kernel Crash Analysis

Thus, reboots become faster in absence of the BIOS stage. Kdump can be used with the kexec application—for example, when the second kernel is booted when the first kernel panics, the second kernel is used to copy the memory dump of first kernel, which can be analyzed with tools such as gdb and crash to determine the panic reasons. In this article, I'll use the terms first kernel for the currently running kernel, second kernel for the kernel run using kexec, and capture kernel for kernel run when current kernel panics.

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The kexec mechanism has components in the kernel as well as in user space. The kernel provides few system calls for kexec reboot functionality. A user space tool called kexec-tools uses those calls and provides an executable to load and boot the second kernel.


Sometimes a distribution also adds wrappers on top of kexec-tools, which helps capture and save the dump for various dump target configurations. In this article, I will use the name distro-kexec-tools to avoid confusion between upstream kexec-tools and distro-specific kexec-tools code.

My example will use the Fedora Linux distribution. The kdump service can be started by executing systemctl start kdump after installation of fedora-kexec-tools.

This service then loads the kernel and initramfs at the suitable location within the crash kernel region so that they can be executed upon kernel panic.

If the kernel panics after the kdump service starts, then the capture kernel is executed, which further executes the vmcore save process from initramfs and reboots to a stable kernel afterward.

Compilation of kexec-tools source code provides an executable called kexec. The same executable can be used to load and execute a second kernel or to load a capture kernel, which can be executed upon kernel panic. Pass initramfs using --initrd.

Kernel crashes explained

A kernel loaded using -l cannot be executed at kernel panic. You must pass -p instead of -l to load the capture kernel that can be executed upon kernel panic. See man kexec for detail about options provided by kexec-tools. Figure 1 shows a flow diagram. Crashkernel memory must be reserved for the capture kernel during booting of the first kernel.

See the kernel-parameters documentation for more ways to pass crash kernel arguments. You can pass kernel and initramfs images to a kexec executable as shown in the typical command of section kexec-tools.


The capture kernel can be the same as the first kernel or can be different. Typically, keep it the same. Typically, you keep a different capture initramfs from the first initramfs, because automating a copy of vmcore in capture initramfs is better. When kexec is executed, it also loads elfcorehdr data and the purgatory executable.

Purgatory can be made optional as well. When the first kernel panics, it does a minimal necessary exit process and switches to purgatory if it exists. Purgatory verifies SHA of loaded binaries and, if those are correct, then it passes control to the capture kernel.If the drivers for your device make many reservations in the DMA32 zone, the Low value also needs to be adjusted. Regardless of the computer on which you analyze the dump, the crash utility will produce output similar to this:.

This is what we need. In the worst case, you may need to export it correctly. You can also prepare the system to boot to another kernel if the system crashes.

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