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. This section covers
fadump mechanisms and how they integrate with RHEL. The
fadump utility is optimized for these expanded dumping features 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
The crash dumping capabilities of IBM POWER systems can be enhanced by enabling the firmware assisted dump (fadump) mechanism.
Install and configure
GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/swap crashkernel=auto rd.lvm.lv=rhel/root rhgb quiet fadump=on"
(Optional) If you want to specify reserved boot memory instead of using the defaults, configure
xxis the amount of the memory required in megabytes:
GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/swap crashkernel=xxM rd.lvm.lv=rhel/root rhgb quiet fadump=on"Important
Red Hat recommends to test all boot configuration options before you execute them. If you observe Out of Memory (OOM) errors when booting from the crash kernel, increase the value specified in
crashkernel=argument until the crash kernel can boot cleanly. Some trial and error may be required in this case.
14.3. Firmware assisted dump mechanisms on IBM Z hardware
IBM Z systems support the following firmware assisted dump mechanisms:
Stand-alone dump (sadump)
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 also initiated from the system console, but retrieves the resulting dump from hardware and copies it to the system for analysis.
These methods (similarly 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.
sadump in detail in the Stand-alone dump program article and
VMDUMP in Creating dumps on z/VM with VMDUMP article.
IBM also has a documentation set for using the dump tools on Red Hat Enterprise Linux 7 in the Using the Dump Tools on Red Hat Enterprise Linux 7.4 article.
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