How should the crashkernel parameter be configured for using kdump on Red Hat Enterprise Linux 5?

Environment

• Red Hat Enterprise Linux 5
• kdump/kexec being used to capture vmcore

Issue

• How should the crashkernel parameter be configured for using kdump on Red Hat Enterprise Linux 5?
• What is the recommended RAM size to reserve for kdump kernel for different different sizes of RAM?
• I am using the crashkernel kernel parameter, but after boot the system writes kernel: crashkernel reservation failed - memory is in use. How to correctly configure the parameter?
• Kernel panic with crashkernel warning Memory for crash kernel (0x0 to 0x0) not within permissible range

Resolution

• The following table can be used as a guide:

crashkernel=memory@offset

+---------------------------------------+
| RAM       | crashkernel | crashkernel |
| size      | memory      | offset      |
|-----------+-------------+-------------|
|  0 - 2G   | 128M        | 16M         | 
| 2G - 6G   | 256M        | 24M         | 
| 6G - 8G   | 512M        | 16M         |
| 8G - 24G  | 768M        | 32M         |
+---------------------------------------+

• For RAM size greater than 24G:

  • Try crashkernel memory 768M and RAM/crashkernel offset of 32, which looks like 768M@32M.
  • If you get an Out-Of-Memory error message, then try with increasing the crashkernel parameter to 896M

• Depending on your system BIOS memory layout, you may need to alter the offset.

• A complete procedure to correctly determine the maximum possible size and precise offset is located at:

  • How to properly calculate the crashkernel setting?

Additional Notes

• Always test to ensure that the kdump service starts correctly and that the system is able to correctly dump by initiating a test.

• The offset for the kdump memory reservation (crashkernel=X@Y) must be specified in RHEL5. Not specifying offset (crashkernel=X) is not a valid configuration under RHEL5, although it is valid under RHEL6.

• kdump fails to initialise with crashkernel=1024M@16M on RHEL5 kernels earlier than 2.6.18-274.el5

• RHEL6's kdump is more memory-efficient than RHEL5's. It is likely more memory will need to be assigned on RHEL5 than on the same system running RHEL6.

  • For settings of kdump on other version of Red Hat Enterprise Linux, please refer to: How should the crashkernel parameter be configured for using kdump on Red Hat Enterprise Linux?

• The crashkernel parameter goes on the kernel line of GRUB's config file /boot/grub/grub.conf and is added to the existing parameters. For example:

  • Before: kernel /vmlinuz ro root=/dev/VolGroup00/LogVol00 rhgb quiet
  • After: kernel /vmlinuz ro root=/dev/VolGroup00/LogVol00 rhgb quiet crashkernel=X@Y

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