http://www.dedoimedo.com/computers/crash-analyze.html
http://fedoraproject.org/wiki/How_to_use_kdump_to_debug_kernel_crashes
http://www.ibm.com/developerworks/cn/linux/l-task-killable/index.html
http://www.2cto.com/os/201204/127771.html
kernel.panic:
the seconds before server rebooting on a panic
但是經過測試 ，panic設置成0，或則 非0，沒區別。
echo "c" > /proc/sysrq-trigger
該cmd會trigger一個crash，此時server會hung住（同時產生vmcore文件在 /var/crash），然後reboot，從測試的時間來看，kernel.panic=0，non -0,都是 一樣的效果。server在vmcore產生完畢後就自動reboot，根本不會考慮panic的時間，個人感覺也沒有必要。
sysrq-trigger is a indirect to set kernel parameter kernel.sysrq
crash need pacakge kernel-debuginfo, but redhat does not provide the kernel-debuginfo package, you need manually add centos-debuginfo repository
http://debuginfo.centos.org/6/x86_64/
because there are more than one version for kernel-debuginfo in repository above, you need show all versions using:
yum --showduplicates list | grep kernel-debuginfo
then choose the same version as your machine:
yum install kernel-debuginfo-2.6.32-431.el6.x86_64