System information

kexec and kdump 205

kexec and kdump

kexec is a tool to boot to another kernel from the currently running one. You can per-

form faster system reboots without any hardware initialization. You can also prepare

the system to boot to another kernel if the system crashes.

18.1 Introduction

With kexec, you can replace the running kernel with another one without a hard re-

boot. The tool is useful for several reasons:

• Faster system rebooting

If you need to reboot the system frequently, kexec can save you significant time.

• Avoiding unreliable firmware and hardware

Computer hardware is complex and serious problems may occur during the system

start-up. You cannot always replace unreliable hardware immediately. kexec boots

the kernel to a controlled environment with the hardware already initialized. The

risk of unsuccessful system start is then minimized.

• Saving the dump of a crashed kernel

kexec preserves the contents of the physical memory. After the production kernel

fails, the capture kernel (an additional kernel running in a reserved memory range)

saves the state of the failed kernel. The saved image can help you with the subse-

quent analysis.