How To Configure Kdump on Linux Servers

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  1. . This are the RPM packages you will need install

          a. kexec-tools --> Provided the kdump configs and services
          b. kernel-kdump --> Kernel with a debuginfo 
          c. crash --> Utility to perform analysis on your kernel crash dump
          d. kernel-debuginfo --> Provide the debugging information
          

   2. . To Modify the system kernel to reserve space for the crash kernel

          Edit the /boot/grub/grub.conf file and add "crashkernel=128M@16M" to the kernel specification to reserve 128MB of
          memory, starting at physical address 0x01000000 (16MB)

       
   3. . Specify where the vmcore should be located

          In /etc/kdump.conf, one can configure different kinds of dump target.

          Here is an example, using NFS as dump target.
          net my.server.com:/export/tmp:

          This will mount the filesystem and copy vmcore to NFS server.
          net my.server.com:/export/tmp

    
   4. . Enable kdump service:

             1. chkconfig kdump on RHEL 6
2. systemctl enable kdump RHEL 7


   5. . Reboot system to put kdump configuration into effect.

          Verify if kdump is active:
             1. cat /proc/cmdline
                ro root=/dev/VolGroup00/LogVol00 rhgb quiet crashkernel=128M@16M
             2. /etc/init.d/kdump status
                Kdump is operational
             3. /sbin/chkconfig --list |grep kdump
                kdump 0:off 1:off 2:on 3:on 4:on 5:on 6:off


   6. . Test kdump by crashing the system:

             1. echo c > /proc/sysrq-trigger
                This causes the kernel to panic, followed by the system restarting into the kdump kernel. When the boot process
                gets to the point where it starts the kdump service, the vmcore should be copied out to disk to the location you
                specified in the /etc/kdump.conf file.

      NOTES: Verify the vmcore is the correct size, it should be about the size of memory on the crashed system.

   1. . To do a crash dumpfile analysis

          Copy the /usr/lib/debug/lib/modules/KERNEL_VER/vmlinux to your /PATH/TO/CRASH/DUMP/DATE/ path

          Run the crash tool to debug it
             1. crash vmlinux vmcore
          Crash tool, behaves like a gdb. First time you want to do in the crash> console is run "log" command to see what's happening to the kernel
          crash> log

          For more info on how to use crash
          crash> help

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