Chapter 14. Firmware assisted dump mechanisms
Firmware assisted dump (fadump) is a dump capturing mechanism, provided as an alternative to the
kdump mechanism on IBM POWER systems. The
kdump mechanisms are useful for capturing core dumps on AMD64 and Intel 64 systems. However, some hardware such as mini systems and mainframe computers, leverage the onboard firmware to isolate regions of memory and prevent any accidental overwriting of data that is important to the crash analysis. The
fadump utility, is optimized for the
fadump mechanisms and their integration with RHEL on IBM POWER systems.
14.1. Firmware assisted dump on IBM PowerPC hardware
fadump utility captures the
vmcore file from a fully-reset system with PCI and I/O devices. This mechanism uses firmware to preserve memory regions during a crash and then reuses the
kdump userspace scripts to save the
vmcore file. The memory regions consist of all system memory contents, except the boot memory, system registers, and hardware Page Table Entries (PTEs).
fadump mechanism offers improved reliability over the traditional dump type, by rebooting the partition and using a new kernel to dump the data from the previous kernel crash. The
fadump requires an IBM POWER6 processor-based or later version hardware platform.
For further details about the
fadump mechanism, including PowerPC specific methods of resetting hardware, see the
The area of memory that is not preserved, known as boot memory, is the amount of RAM required to successfully boot the kernel after a crash event. By default, the boot memory size is 256MB or 5% of total system RAM, whichever is larger.
kexec-initiated event, the
fadump mechanism uses the production kernel to recover a crash dump. When booting after a crash, PowerPC hardware makes the device node
/proc/device-tree/rtas/ibm.kernel-dump available to the
proc filesystem (
fadump-aware kdump scripts, check for the stored
vmcore, and then complete the system reboot cleanly.
14.2. Enabling firmware assisted dump mechanism
You can enhance the crash dumping capabilities of IBM POWER systems by enabling the firmware assisted dump (
In the Secure Boot environment, the
GRUB2 boot loader allocates a boot memory region, known as the Real Mode Area (RMA). The RMA has a size of 512 MB, which is divided among the boot components and, if a component exceeds its size allocation,
GRUB2 fails with an out-of-memory (
Do not enable firmware assisted dump (
fadump) mechanism in the Secure Boot environment on RHEL 9.1 and early versions. The
GRUB2 boot loader fails with the following error:
error: ../../grub-core/kern/mm.c:376:out of memory. Press any key to continue…
The system is recoverable only if you increase the default
initramfs size due to the
For information about workaround methods to recover the system, see the System boot ends in GRUB Out of Memory (OOM) article.
- You have root privileges.
Configure the default value for
# kdumpctl reset-crashkernel –fadump=on --kernel=ALL
(Optional) Reserve boot memory instead of the default value.
# grubby --update-kernel ALL --args=”fadump=on crashkernel=xxM"
xxis the required memory size in megabytes.Note
When specifying boot configuration options, test the configurations by rebooting the kernel with
kdumpenabled. If the
kdumpkernel fails to boot, increase the
crashkernelvalue gradually to set an appropriate value.
Reboot for changes to take effect.
14.3. Firmware assisted dump mechanisms on IBM Z hardware
IBM Z systems supports two firmware assisted dump mechanisms: Stand-alone dump (
VMDUMP dump file.
kdump infrastructure is supported and utilized on IBM Z systems. However, using one of the firmware assisted dump (
fadump) methods for IBM Z can provide various benefits:
sadumpmechanism is initiated and controlled from the system console, and is stored on an
VMDUMPmechanism is similar to
sadump. This tool is initiated from the system console, but retrieves the resulting dump from hardware and copies it to the system for analysis.
These methods, similar to other hardware-based dump mechanisms, have the ability to capture the state of a machine in the early boot phase, before the
VMDUMPcontains a mechanism to receive the dump file into a Red Hat Enterprise Linux system, the configuration and control of
VMDUMPis managed from the IBM Z Hardware console.
14.4. Using sadump on Fujitsu PRIMEQUEST systems
sadump mechanism is designed to provide a
fallback dump capture in an event when
kdump is unable to complete successfully. The
sadump mechanism is invoked manually from the system Management Board (MMB) interface. Using MMB, configure
kdump like for an Intel 64 or AMD 64 server and then perform the following additional steps to enable
Add or edit the following lines in the
/etc/sysctl.conffile to ensure that
kdumpstarts as expected for
In particular, ensure that after
kdump, the system does not reboot. If the system reboots after
kdumphas fails to save the
vmcorefile, then it is not possible to invoke the
- The FUJITSU Server PRIMEQUEST 2000 Series Installation Manual