12.2.1 Configuring and Using Kdump

The software described in this documentation is either in Extended Support or Sustaining Support. See https://www.oracle.com/us/support/library/enterprise-linux-support-policies-069172.pdf for more information.
Oracle recommends that you upgrade the software described by this documentation as soon as possible.

12.2.1 Configuring and Using Kdump

During installation, you are given the option of enabling Kdump and specifying the amount of memory to reserve for it. If you prefer, you can enable kdump at a later time as described in this section.

If the kexec-tools and system-config-kdump packages are not already installed on your system, use yum to install them.

To enable Kdump by using the Kernel Dump Configuration GUI.

Enter the following command.
```
# system-config-kdump
```
The Kernel Dump Configuration GUI starts. If Kdump is currently disabled, the green Enable button is selectable and the Disable button is greyed out.
Click Enable to enable Kdump.
You can select the following settings tags to adjust the configuration of Kdump.
Basic Settings
Allows you to specify the amount of memory to reserve for Kdump. The default setting is 128 MB.
Target Settings
Allows you to specify the target location for the vmcore dump file on a locally accessible file system, to a raw disk device, or to a remote directory using NFS or SSH over IPv4. The default location is /var/crash.
You cannot save a dump file on an eCryptfs file system, on remote directories that are NFS mounted on the rootfs file system, or on remote directories that access require the use of IPv6, SMB, CIFS, FCoE, wireless NICs, multipathed storage, or iSCSI over software initiators to access them.
Filtering Settings
Allows to select which type of data to include in or exclude from the dump file. Selecting or deselecting the options alters the value of the argument that Kdump specifies to the -d option of the core collector program, makedumpfile.
Expert Settings
Allows you to choose which kernel to use, edit the command line options that are passed to the kernel and the core collector program, choose the default action if the dump fails, and modify the options to the core collector program, makedumpfile.
For example, if Kdump fails to start, and the following error appears in /var/log/messages, set the offset for the reserved memory to 48 MB or greater in the command line options, for example crashkernel=128M@48M:
```
kdump: No crashkernel parameter specified for running kernel
```
The Unbreakable Enterprise Kernel supports the use of the crashkernel=auto setting for UEK Release 3 Quarterly Update 1 and later. If you use the crashkernel=auto setting, the output of the dmesg command shows crashkernel=XM@0M, which is normal. The setting actually reserves 128 MB plus 64 MB for each terabyte of physical memory.
Note
You cannot configure crashkernel=auto for Xen or for the UEK prior to UEK Release 3 Quarterly Update 1. Only standard settings such as crashkernel=128M@48M are supported. For systems with more than 128 GB of memory, the recommended setting is crashkernel=512M@64M.
Click Help for more information on these settings.
Click Apply to save your changes. The GUI displays a popup message to remind you that you must reboot the system for the changes to take effect.
Click OK to dismiss the popup messages.
Select File > Quit.
Reboot the system at a suitable time.