Chapter 21. Supported kdump configurations and targets

In order for kdump to be able to capture a kernel crash dump and save it for further analysis, a part of the system memory has to be permanently reserved for the capture kernel. When reserved, this part of the system memory is not available to the main kernel.

The memory requirements vary based on certain system parameters. One of the major factors is the system’s hardware architecture. To find out the exact machine architecture (such as Intel 64 and AMD64, also known as x86_64) and print it to standard output, use the following command:

$ uname -m

With the stated list of minimum memory requirements, you set the appropriate memory size to automatically reserve a memory for kdump on the latest available versions. The memory size depends on the system’s architecture and total available physical memory.

On many systems, kdump is able to estimate the amount of required memory and reserve it automatically. The automatic memory reservation mechanism is enabled by default and requires the systems to have available memory more than the minimum threshold, which varies based on the system architecture.

The kexec-tools utility, by default, configures the crashkernel command line parameter and reserves a certain amount of memory for kdump. For the default memory reservation to work, a certain amount of total memory must be available in the system. The amount of memory required differs based on the system’s architecture. If the system has memory less than the specified threshold value, you must configure the memory manually.

When a kernel crash is captured, the vmcore dump file can be saved directly to a device, stored as a file on a local file system, or sent over a network. With the list of dump targets, you can understand the targets that are currently supported or not supported by kdump.

To reduce the size of the dump file, kdump uses the makedumpfile core collector to compress the data and optionally to omit unwanted information. With the list of filtering levels, you can understand the levels that are currently supported by the makedumpfile utility.

By default, when kdump fails to create a core dump, the operating system reboots. You can, however, configure kdump to perform a different operation in case it fails to save the core dump to the primary target. With the lists of default actions, you can understand the responses that are currently supported.

The final_action parameter enables you to use certain additional operations such as reboot, halt, and poweroff actions after a successful kdump or when an invoked failure_action mechanism using shell or dump_to_rootfs completes. If the final_action option is not specified, it defaults to reboot.

The failure_action parameter specifies the action to perform when a dump fails in the event of a kernel crash. The default action for failure_action is reboot, which reboots the system.

failure_action specifies one of the following actions to take: