How to test watchdog operation in Ubuntu Server 18.04 \ how to call KERNEL PANIC in Ubuntu Server 18.04?

Question

System administration

I'm testing the watchdog in Proxmox 5.1.
In debian 9.4, ubuntu 16.04 and gentoo checked - everything works. And with ubuntu 18.04, it turned out to be more difficult to check.
The procedure is as follows:
In the config of the virtual machine on the hypervisor, I registered

watchdog: model=i6300esb,action=reset

Inside the virtual machine itself, I put a watchdog from a turnip, write it in /etc/default/watchdog

watchdog_module=i6300esb

Executed systemctl enable watchdog. After the reboot, the daemon starts stably, sees the /dev/watchdog device.
It remains to check his work, and then the problems began. In the aforementioned OSes, I did

echo c > /proc/sysrq-trigger

The system crashed into kernel panic and a minute later watchdog restarted the virtual machine.
Ubuntu 18.04 turned out to be stronger: the first three times after executing the command, it instantly rebooted, without the help of a watchdog. For the fourth time onwards, when I try to run the command, it says:

#echo c > /proc/sysrq-trigger
SysRq : This sysrq operation is disabled.

Accordingly, the question is: how is it guaranteed to cause a kernel panic and thus check the watchdog?

Answer 1

You can run a "fork bomb", this is a process that endlessly spawns new processes until the system resources run out.

#!/bin/bash
:(){ :|:& };: