Watchdog on VIM3

[JJ1997]

Which Khadas SBC do you use?

VIM3 Basic

Which system do you use? Android, Ubuntu, OOWOW or others?

Ubuntu

Which version of system do you use? Khadas official images, self built images, or others?

vim3-ubuntu-20.04-gnome-linux-4.9-fenix-1.1.1-220725-emmc.img

Please describe your issue below:

I followed this doc and set watchdog on VIM3. But I found that, regardless of whether the systemctl watchdog.service is enabled or not, the system will restart immediately after I use the command “echo c | sudo tee /proc/sysrq-trigger” to crash the kernel.

Does the internal watchdog here refer to the hardware watchdog? Does that mean there is some other service that activates the watchdog?

And how does this differ from configuring the watchdog in the /etc/systemd/system.conf by setting “RuntimeWatchdogSec=, RebootWatchdogSec=, KExecWatchdogSec=”?

Thanks a lot
@Frank @numbqq

[ivan.li]

Hi~@JJ1997
It does, and our documentation needs to be updated 。

@JJ1997

I followed this doc and set watchdog on VIM3. But I found that, regardless of whether the systemctl watchdog.service is enabled or not, the system will restart immediately after I use the command “echo c | sudo tee /proc/sysrq-trigger” to crash the kernel.

This one is a pure software implementation of linux watchdog.

@JJ1997

Does the internal watchdog here refer to the hardware watchdog? Does that mean there is some other service that activates the watchdog?

The question is which configuration file the watchdog service will read.

@JJ1997

And how does this differ from configuring the watchdog in the /etc/systemd/system.conf by setting “RuntimeWatchdogSec=, RebootWatchdogSec=, KExecWatchdogSec=”?

[numbqq]

@JJ1997

But I found that, regardless of whether the systemctl watchdog.service is enabled or not, the system will restart immediately after I use the command “echo c | sudo tee /proc/sysrq-trigger” to crash the kernel.

It is beacuse the configuration CONFIG_PANIC_TIMEOUT=5 is enabled, so when the system crash it will reboot after the timeout 5 seconds.

How to disable this feature? You can follow the steps below to setup the panic timeout to 0 which means not reboot.

echo 0 | sudo tee /sys/module/kernel/parameters/panic

Then enable the watchdog and try to trigger a crash the system should reboot after the watchdog timeout.

echo c | sudo tee /proc/sysrq-trigger

[christian5271]

While testing the watchdog service a while ago on Ubuntu 20.04 LTS, I noticed it generates a false positive alarm whenever I download large software over WiFi. For some reason, the download ramps up the Kernel load and that triggers the watchdog eventually. In the end, I could not download the software (a container image) at all because the device was always reset before finish. This appears to be a Kernel issue to me which is still present in version 6.0.0.

In the end, I had to deactivate the watchdog again and since then I had no spurious resets anymore.