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10
OS Fault Location
10.1
Configuring the Memory Dump Tools
When an OS crashes, sufficient information needs to be collected to analyze the
cause of the crash. Memory dump is a mechanism that saves the memory
information of the OS as DUMP files in case of an OS crash.
It is supported on various operating systems such as Linux, Windows, and VMware.
10.1.1 Related Concepts
Linux kernel is a rather robust entity. It is stable and fault-tolerable and usually
does not suffer irrecoverable errors that crash the entire system. However, these
kinds of problems cannot be completely avoided, and they are known as kernel
crashes. Kdump is a tool provided by Linux to detect, collect, and analyze crashes.
You can use this tool to locate the root cause of crashes and find solutions to
critical bugs.
Kdump, which is implemented based on kexec, is a reliable kernel crash dumping
mechanism. When the OS crashes, kexec is used to boot into a second kernel in
order to capture and dump the kernel crash information. With kexec, kdump can
directly use the reserved memory to boot into the kdump kernel without going
through BIOS. When the OS crashes, it captures and retains the crash information
of the first kernel for debugging and analysis. It is generally used to analyze
system crashes, kernel panics, and deadlocks. If the OS release version you are
using does not come with the kdump service, contact the OS provider if needed.
Kexec is a fastboot mechanism that allows booting a Linux kernel from the context
of an already running kernel without going through BIOS. BIOS can be very time
consuming especially on big servers with many peripheral connections. This saves
time for the developers who boot a machine numerous times.
The kdump mechanism involves 2 types of kernel:
Standard (production) kernel, which is used to run services.
Crash (capture) kernel, which is used to collect crash information.
Kdump is a new reliable kernel crash dumping mechanism. The crash dump is
captured from the context of a freshly booted kernel and not from the context of
the crashed kernel. Kdump uses kexec to boot into a second kernel whenever the
system crashes. This second kernel, often called a crash or a capture kernel, boots
with very little memory and captures the dump image. This portion of memory is
reserved by the standard kernel for kexec to boot into the crash kernel, which is
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