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Chapter 18. Supported kdump configurations and targets

The kdump mechanism is a feature of the Linux kernel that generates a crash dump file when a kernel crash occurs. The kernel dump file has critical information that helps to analyze and determine the root cause of a kernel crash. The crash can be because of various factors, hardware issues or third-party kernel modules problems, to name a few.

With the provided information and procedures, you understand the supported configurations and targets on your RHEL 8 systems and properly configure kdump and validate it’s working.

18.1. Memory requirements for kdump

For kdump to capture a kernel crash dump and save it for further analysis, a part of the system memory should 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 can 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.

Table 18.1. Minimum amount of reserved memory required for kdump

ArchitectureAvailable MemoryMinimum Reserved Memory

AMD64 and Intel 64 (x86_64)

1 GB to 4 GB

192 MB of RAM

4 GB to 64 GB

256 MB of RAM

64 GB and more

512 MB of RAM

64-bit ARM architecture (arm64)

2 GB and more

480 MB of RAM

IBM Power Systems (ppc64le)

2 GB to 4 GB

384 MB of RAM

4 GB to 16 GB

512 MB of RAM

16 GB to 64 GB

1 GB of RAM

64 GB to 128 GB

2 GB of RAM

128 GB and more

4 GB of RAM

IBM Z (s390x)

1 GB to 4 GB

192 MB of RAM

4 GB to 64 GB

256 MB of RAM

64 GB and more

512 MB of RAM

On many systems, kdump is able to estimate the amount of required memory and reserve it automatically. This behavior is enabled by default, but only works on systems that have more than a certain amount of total available memory, which varies based on the system architecture.

Important

The automatic configuration of reserved memory based on the total amount of memory in the system is a best effort estimation. The actual required memory may vary due to other factors such as I/O devices. Using not enough of memory might cause that a debug kernel is not able to boot as a capture kernel in case of a kernel panic. To avoid this problem, sufficiently increase the crash kernel memory.

18.2. Minimum threshold for automatic memory reservation

On some systems, it is possible to allocate memory for kdump automatically, either by using the crashkernel=auto parameter in the boot loader configuration file, or by enabling this option in the graphical configuration utility. For this automatic reservation to work, however, a certain amount of total memory needs to be available in the system. The memory requirement varies based on the system’s architecture. If the system has memory less than the specified threshold value, you must configure the memory manually.

Table 18.2. Minimum Amount of Memory Required for Automatic Memory Reservation

ArchitectureRequired Memory

AMD64 and Intel 64 (x86_64)

2 GB

IBM Power Systems (ppc64le)

2 GB

IBM  Z (s390x)

4 GB

Note

The crashkernel=auto option in the boot command line is no longer supported on RHEL 9 and later releases.

18.3. Supported kdump targets

When a kernel crash occurs, the operating system saves the dump file on the configured or default target location. You can save the dump file either directly to a device, store as a file on a local file system, or send the dump file over a network. With the following list of dump targets, you can know the targets that are currently supported or not supported by kdump.

Table 18.3. kdump targets on RHEL 8

Target typeSupported TargetsUnsupported Targets

Physical storage

  • Logical Volume Manager (LVM).
  • Thin provisioning volume.
  • Fibre Channel (FC) disks such as qla2xxx, lpfc, bnx2fc, and bfa.
  • An iSCSI software-configured logical device on a networked storage server.
  • The mdraid subsystem as a software RAID solution.
  • Hardware RAID such as cciss, hpsa, megaraid_sas, mpt2sas, and aacraid.
  • SCSI and SATA disks.
  • iSCSI and HBA offloads.
  • Hardware FCoE such as qla2xxx and lpfc.
  • BIOS RAID.
  • Software iSCSI with iBFT. Currently supported transports are bnx2i, cxgb3i, and cxgb4i.
  • Software iSCSI with a hybrid device driver such as be2iscsi.
  • Fibre Channel over Ethernet (FCoE).
  • Legacy IDE.
  • GlusterFS servers.
  • GFS2 file system.
  • Clustered Logical Volume Manager (CLVM).
  • High availability LVM volumes (HA-LVM).

Network

  • Hardware using kernel modules: tg3, igb, ixgbe, sfc, e1000e, bna, cnic, netxen_nic, qlge, bnx2x, bnx, qlcnic, be2net, enic, virtio-net, ixgbevf, igbvf.
  • IPv4 protocol.
  • Network bonding on different devices, such as Ethernet devices or VLAN.
  • VLAN network.
  • Network Bridge.
  • Network Teaming.
  • Tagged VLAN and VLAN over a bond.
  • Bridge network over bond, team, and VLAN.
  • IPv6 protocol.
  • Wireless connections.
  • InfiniBand networks.
  • VLAN network over bridge and team.

Hypervisor

  • Kernel-based virtual machines (KVM).
  • Xen hypervisor in certain configurations only.
  • VMware ESXi 4.1 and 5.1.
  • Hyper-V 2012 R2 on RHEL Gen1 UP Guest only.
 

File systems

The ext[234], XFS, and NFS file systems.

The Btrfs file system.

Firmware

  • BIOS-based systems.
  • UEFI Secure Boot.
 

Additional resources

18.4. Supported kdump filtering levels

To reduce the size of the dump file, kdump uses the makedumpfile core collector to compress the data and also exclude unwanted information, for example, you can remove hugepages and hugetlbfs pages by using the -8 level. The levels that makedumpfile currently supports can be seen in the table for Filtering levels for `kdump` .

Table 18.4. Filtering levels for kdump

OptionDescription

1

Zero pages

2

Cache pages

4

Cache private

8

User pages

16

Free pages

Additional resources

18.5. Supported default failure responses

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.

Table 18.5. Failure responses for kdump

OptionDescription

dump_to_rootfs

Attempt to save the core dump to the root file system. This option is especially useful in combination with a network target: if the network target is unreachable, this option configures kdump to save the core dump locally. The system is rebooted afterwards.

reboot

Reboot the system, losing the core dump in the process.

halt

Halt the system, losing the core dump in the process.

poweroff

Power off the system, losing the core dump in the process.

shell

Run a shell session from within the initramfs, allowing the user to record the core dump manually.

final_action

Enable additional operations such as reboot, halt, and poweroff actions after a successful kdump or when shell or dump_to_rootfs failure action completes. The default final_action option is reboot.

18.6. Using final_action parameter

When kdump succeeds or if kdump fails to save the vmcore file at the configured target, you can perform additional operations like reboot, halt, and poweroff by using the final_action parameter. If the final_action parameter is not specified, reboot is the default response.

Procedure

  1. Edit the `/etc/kdump.conf file and add the final_action parameter.

    final_action <reboot | halt | poweroff>
  2. Restart the kdump service:

    kdumpctl restart