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how_to_configure_kernel2_dumps_on_RHEL5.txt
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Kernel dumps may provide invalueable insights when debugging serious issues. This howto shows you step by step how to setup kdump on RHEL 5 to dump vmcores to a remote server.
=== Step-by-Step Guide ===
1.Download kernel-debuginfo-common and kernel-debuginfo RPMs for your kernel version (uname -r) from Red Hat FTP server.
2.Install kernel-debuginfo-common and kernel-debuginfo on the system:
# ls *.rpm
kernel-debuginfo-2.6.18-128.1.10.el5.x86_64.rpm kernel-debuginfo-common-2.6.18-128.1.10.el5.x86_64.rpm
# rpm -ivh *.rpm
warning: kernel-debuginfo-2.6.18-128.1.10.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
Preparing... ########################################### [100%]
1:kernel-debuginfo-common ########################################### [ 50%]
2:kernel-debuginfo ########################################### [100%]
3.Also install kexec-tools and crash:
# yum install kexec-tools crash
4.Append "crashkernel=128M@16M" to the kernel parameters in /boot/grub/grub.conf:
# grubby --update-kernel=ALL --args="crashkernel=128M@16M"
5.Reboot
6.Check that the crash kernel has been loaded:
# cat /proc/iomem | grep Crash\ kernel
01000000-08ffffff : Crash kernel
7.Configure kdump via the following command:
# echo > /etc/kdump.conf << EOF
net root@kdump_remote_server
core_collector makedumpfile -d 31 -c
EOF
8.Propagate SSH keys so that the vmcore could be sent via scp without the need to enter any password:
# service kdump propagate
9.Create kdump ramdisk for collecting the vmcore
# service kdump restart
or /bin/systemctl restart kdump.service
10.Sync all filesystems:
# sync
11.Provoke a kernel panic with:
# echo "1" > /proc/sys/kernel/sysrq
# echo "c" > /proc/sysrq-trigger
12.Now the crash kernel should get booted and on the remote system a vmcore should get created under /var/crash:
# tree /var/crash
/var/crash
|-- 192.168.12.227-2010-01-21-20:16:16
`-- vmcore.flat
13.The vmcore.flat needs to be processed in order to analyze the core dump via the crash utility:
# cat "vmcore.flat" | makedumpfile -R "/tmp/vmcore"
The dumpfile is saved to /tmp/vmcore.
makedumpfile Completed.
14.Now you may analyze the vmcore with the crash utility:
# crash /usr/lib/debug/lib/modules/`uname -r`/vmlinux /tmp/vmcore
crash 4.0-8.9.1.el5
Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Red Hat, Inc.
Copyright (C) 2004, 2005, 2006 IBM Corporation
Copyright (C) 1999-2006 Hewlett-Packard Co
Copyright (C) 2005, 2006 Fujitsu Limited
Copyright (C) 2006, 2007 VA Linux Systems Japan K.K.
Copyright (C) 2005 NEC Corporation
Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc.
Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc.
This program is free software, covered by the GNU General Public License,
and you are welcome to change it and/or distribute copies of it under
certain conditions. Enter "help copying" to see the conditions.
This program has absolutely no warranty. Enter "help warranty" for details.
GNU gdb 6.1
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu"...
KERNEL: /usr/lib/debug/lib/modules/2.6.18-128.1.10.el5/vmlinux
DUMPFILE: /tmp/vmcore [PARTIAL DUMP]
CPUS: 1
DATE: Thu Jan 21 20:21:20 2010
UPTIME: 00:03:10
LOAD AVERAGE: 1.09, 0.46, 0.17
TASKS: 445
NODENAME: vrhel03
RELEASE: 2.6.18-128.1.10.el5
VERSION: #1 SMP Wed Apr 29 13:53:08 EDT 2009
MACHINE: x86_64 (2666 Mhz)
MEMORY: 1 GB
PANIC: "SysRq : Trigger a crashdump"
PID: 7835
COMMAND: "bash"
TASK: ffff81040699d0c0 [THREAD_INFO: ffff8103fed24000]
CPU: 1
STATE: TASK_RUNNING (SYSRQ)
crash>