Initiating a dump

A kernel panic automatically triggers the dump process with kdump. When your Linux® system does not respond and kdump is not triggered automatically, depending on your system environment, there are additional methods for triggering the dump process.

About this task

With kdump installed, a kernel panic or PSW restart trigger kdump rather than the shutdown actions defined in /sys/firmware. The definitions in /sys/firmware are used only if an integrity check for kdump fails (see also Failure recovery and backup tools and dumpconf - Configure panic or PSW restart action).

To trigger kdump, use one of the methods according to your environment:

  • For Linux on KVM: Issue the virsh inject-nmi command on the KVM host.
  • For Linux on z/VM®: Run the z/VM CP system restart command.
  • For Linux in LPAR mode: Run the PSW restart task on the HMC.
In all three environments, you can use the following methods to trigger a dump.
The diag288 watchdog
You can use the diag288 watchdog to trigger kdump. The default setup triggers the correct actions.
The magic sysrequest feature
Crash the kernel through the magic sysrequest feature, for example by writing c to /proc/sysrq-trigger.
# echo c > /proc/sysrq-trigger
Hint: You might have to write 1 to /proc/sys/kernel/sysrq first to enable the sysrequest feature.
For more information about the diag288 watchdog and about the magic sysrequest feature, see Device Drivers, Features, and Commands on Red Hat Enterprise Linux 8.5, SC34-7715.

Results

After kdump is triggered, first kernel messages from the booting kdump kernel and later dump progress messages are issued. The messages are written to the Operating System Messages applet of the HMC for LPAR, to the 3270 terminal for z/VM, or to the console that has been configured for your KVM virtual server. The kdump scripts copy the dump and reboot automatically.

What to do next

Verify that your production system is up and running again. Send the created dump to a support organization.