Kexec & Kdump Understanding Linux Crash Dump

[이누기]

Subhendu_Ghosh-KExecKDump.pdf

>>>설정법 참고

How do I use the diskdump utility to capture a vmcore in Red Hat Enterprise Linux 3 and 4?

http://kbase.redhat.com/faq/docs/DOC-7075

How do I configure kexec/kdump on Red Hat Enterprise Linux 5?

http://kbase.redhat.com/faq/docs/DOC-6039

How do I run commands using kdump, before vmcore is saved?

http://kbase.redhat.com/faq/docs/DOC-2164

How do I configure Xendump on Red Hat Enterprise Linux 5?

http://kbase.redhat.com/faq/docs/DOC-9864

Documentation for Kdump - The kexec-based Crash Dumping Solution

http://www.cyberciti.biz/files/linux-kernel/Documentation/kdump/kdump.txt

http://wiki.verwilst.be/howto:kdump

Debugging Linux 2.6 kernels with Kexec/Kdump

2G이상인 경우 256M로 권장합니다. 또한 crashkernel의 사이즈의 크기는 현재 사용중인 메모리와 거의 무관합니다.

kdump는 kexec의 사용으로 bios없이 crash capture kernel의 부팅으로 현재의 메모리를 덤프합니다.

Load the Dump-capture Kernel

============================

After booting to the system kernel, load the dump-capture kernel using

the following command:

   kexec -p <dump-capture-kernel> \

   --initrd=<initrd-for-dump-capture-kernel> --args-linux \

   --append="root=<root-dev> init 1 irqpoll"

Notes on loading the dump-capture kernel:

* <dump-capture-kernel> must be a vmlinux image (that is, an

  uncompressed ELF image). bzImage does not work at this time.

* By default, the ELF headers are stored in ELF64 format to support

  systems with more than 4GB memory. The --elf32-core-headers option can

  be used to force the generation of ELF32 headers. This is necessary

  because GDB currently cannot open vmcore files with ELF64 headers on

  32-bit systems. ELF32 headers can be used on non-PAE systems (that is,

  less than 4GB of memory).

* The "irqpoll" boot parameter reduces driver initialization failures

  due to shared interrupts in the dump-capture kernel.

* You must specify <root-dev> in the format corresponding to the root

  device name in the output of mount command.

* "init 1" boots the dump-capture kernel into single-user mode without

  networking. If you want networking, use "init 3."

Kernel Panic

============

After successfully loading the dump-capture kernel as previously

described, the system will reboot into the dump-capture kernel if a

system crash is triggered.  Trigger points are located in panic(),

die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).

The following conditions will execute a crash trigger point:

If a hard lockup is detected and "NMI watchdog" is configured, the system

will boot into the dump-capture kernel ( die_nmi() ).

If die() is called, and it happens to be a thread with pid 0 or 1, or die()

is called inside interrupt context or die() is called and panic_on_oops is set,

the system will boot into the dump-capture kernel.

On powererpc systems when a soft-reset is generated, die() is called by all cpus and the system system will boot into the dump-capture kernel.

For testing purposes, you can trigger a crash by using "ALT-SysRq-c",

"echo c > /proc/sysrq-trigger or write a module to force the panic.

Write Out the Dump File

=======================

After the dump-capture kernel is booted, write out the dump file with

the following command:

   cp /proc/vmcore <dump-file>

You can also access dumped memory as a /dev/oldmem device for a linear

and raw view. To create the device, use the following command:

    mknod /dev/oldmem c 1 12

Use the dd command with suitable options for count, bs, and skip to

access specific portions of the dump.

To see the entire memory, use the following command:

   dd if=/dev/oldmem of=oldmem.001

2G이상인 경우 256M로 권장합니다.

이상입니다.