# cp /etc/fstab /etc/fstab.nokdump <- in case you're using NFS mounts to save the core dumps
3. Enable Magic SysRQ
Edit /etc/sysconfig/sysctl using your favorite editor (e.g. vi).
Change the ENABLE_SYSRQ configuration to
The system now either needs to be reboot for the setting above to take effect. Alternatively, you can issue the following command:
# echo 1 > /proc/sys/kernel/sysrq
3. Check Packages
Confirm that kdump, kexec-tools, and makedumpfile are installed.
# rpm -qa | grep kdump
# rpm -qa | grep kexec-tools
# rpm -qa | grep makedumpfile
4. Configure Kdump
Go to System > Kernel Kdump
Under Start-Up change Enable/Disable Kdump to Enable Kdump and the Kdump Memory [MB] to 768MB.
Go to Dump Filtering and deselect Free Pages in order to decrease the vmcore file.
The corresponding setting in /etc/sysconfig/kdump is KDUMP_DUMPLEVEL="16".
By default Kdump will dump the files in /var/crash (see figure below). If there's enough space on the local partition to accomodate the core dumps, leave this unchanged.
In our lab we have an NFS share where we save all the core dumps and this NFS share gets mounted automatically during boot time (/etc/fstab).
One thing we noticed when using NFS shares is that if you simply type the mount location in "Directory for Saving Dumps," (e.g. /mnt/kdump), kdump tries to save the files to /root/mnt/kdump which is not the right location. We had to choose Browse and browse to /mnt/kdump.
The corresponding setting in /etc/sysconfig/kdump is KDUMP_SAVEDIR="file:///mnt/kdump".
Press F10 to save the changes to exit out of YaST2. YaST2 will automatically modify the default entry in /boot/grub/menu.lst file to include the crashkernel memory reservation defined earlier. You can verify it by looking at the menu.lst file.
cishanar01:/root # cat /boot/grub/menu.lst
# Modified by YaST2. Last modification on Fri Dec 28 13:33:13 EST 2012
##YaST - activate
serial --unit=0 --speed=115200
terminal --timeout=8 serial console
###Don't change this comment - YaST2 identifier: Original name: linux###
title Serial -- SUSE Linux Enterprise Server 11 SP1 - 188.8.131.52-0.7
Once the system experiences a kernel panic or kernel oops, SysRQ should trigger automatically to boot into the crash kernel using kexec and dump the core. If for some reason you would like to manually trigger a crash dump, you can define a keyboard sequence from UCSM:
Go to UCSM > right-click on the blade > KVM console > User Defined Macro > Manage.
Click on New > Create the "magic SysRq" keyboard combination "Print Screen / SysRq + C".
If this macro is issued, a crash will occur. You can also trigger a crash from the command line:
# echo c > /proc/sysrq-trigger
8. Kdump Not Working
a) In the lab we found that kdump would not work if the crash kernel memory reservation was set higher than 1024MB. If 768MB does not work for you, try lowering or increasing that value. If changing the value, we suggest doing it via YaST so that menu.lst gets updated automatically.
b) If using an NFS share, the share might not get mounted unless the crash kernel boots in runlevel 3. To achieve this, add the following line to /etc/sysconfig/kdump. The default value is 1.
c) Some kdump documents suggest adding maxcpus=1 to KDUMP_COMMANDLINE_APPEND if the kernel was built with SMP support.
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