Re: watchdog: how to enable?

[Guenter Roeck <linux@roeck-us.net>]

On 11/16/19 10:34 AM, Muni Sekhar wrote:
> On Sat, Nov 16, 2019 at 9:31 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> On 11/15/19 7:03 PM, Muni Sekhar wrote:
>> [ ... ]
>>>>
>>>> Another possibility, of course, might be to enable a hardware watchdog
>>>> in your system (assuming it supports one). I personally would not trust
>>>> the NMI watchdog because to detect a system hang, after all, there are
>>>> situations where even NMIs no longer work.
>>>
>>> >From dmesg , Is it possible to know whether my system supports
>>> hardware watchdog or not?
>>> I assume that my system supports the hardware watchdog , then how to
>>> enable the hardware watchdog to debug the system freeze issues?
>>>
>>
>> Hardware watchdog support really depends on the board type. Most PC
>> mainboards support a watchdog in the Super-IO chip, but on some it is
>> not wired correctly. On embedded boards it is often built into the SoC.
>> The easiest way to see if you have a watchdog would be to check for the
>> existence of /dev/watchdog. However, on a PC that would most likely
>> not be there because the necessary module is not auto-loaded.
>> If you tell us your board type, or better the Super-IO chip on the board,
>> we might be able to help.
> 
> I’m having two same configuration systems, in one system I installed
> the Vanilla kernel and I see the /dev/watchdog and /dev/watchdog0
> nodes. In other system I’m running with ubuntu distribution kernel,
> but I don’t see any watchdog device node. So it looks like I need to
> manually load the kernel module in distro kernel. Is there a way to
> know what is the corresponding kernel module for  /dev/watchdog node?
> 
> # ls -l /dev/watchdog*
> crw------- 1 root root  10, 130 Nov 15 17:15 /dev/watchdog
> crw------- 1 root root 248,   0 Nov 15 17:15 /dev/watchdog0
> 
> # ps -ax | grep watchdog
>    678 ?        S      0:00 [watchdogd]
> 
> Regarding Super-IO chip, how to find out the Super-IO chip model?
> 
You could try to run sensors-detect (from the "sensors" package).

If you can boot a system with /dev/watchdog0, you should see the type
in /sys/class/watchdog/watchdog0/identity.

Also, you can test if the watchdog works with "sudo cat /dev/watchdog",
assuming the watchdog daemon is not running. The watchdog works if the
system reboots after the watchdog times out (/sys/class/watchdog/watchdog0/timeout
is the timeout in seconds).

>>
>> Note though that this won't help to debug the problem. A hardware
>> watchdog resets the system. It helps to recover, but it is not intended
>> to help with debugging.
> How do I use the hardware watchdog to reset my system when system is
> frozen? It helps me to collect the crashdump and finally helps me to
> find the root cause for the system frozen issue.
> 
There won't be a crashdump. It just hard-resets the system.

Guenter