Watchdog on the RPi4

Question

Does the Raspberry Pi 4 have a hardware watchdog timer like the RPi3 does? If it does, which kernel module should I load in order to use it?

I'm running Raspbian Buster, kernel 4.19.93-v7l+

Thanks.

Answer 1

To check if the watchdog is available, you can run wdctl which gives you a bit more info than just looking at /dev/watchdog.

To start using the watchdog, you can still use the old watchdog daemon mentioned in the other answers, but since 2012 systemd has had built in support for watchdogs that doesn't require installing anything else and offers better compatibility with the shutdown/reboot process.

To use this, edit /etc/systemd/system.conf and set these values as required:

• RuntimeWatchdogSec - reboot the system if nothing contacts the watchdog within this time (specify the value like 2min, 10s, etc.) This defaults to off, meaning the system will never reboot when it freezes. For Raspberry Pi, this value must be shorter than 15s to avoid a reboot loop in present kernels (driver patch in progress - Dec 2023).
• RebootWatchdogSec - different timeout used when rebooting, in case you need more (or less) time. Defaults to 10min. Note that this only applies during the last phase of the reboot, once all running programs have been terminated. If your programs take too long to shut down, this value won't help (see below).
• ShutdownWatchdogSec - this is no longer used, it was renamed to RebootWatchdogSec in July 2019.
• KExecWatchdogSec - ignore this unless you know what kexec is and you know you are using it. (It's used when faking a reset by just restarting the kernel - the lack of a hardware reset means the watchdog is still running and may expire before everything has finished loading again).
• WatchdogDevice - this can be ignored as the default of /dev/watchdog is fine.
• DefaultTimeoutStopSec - how long to wait for each program to exit when shutting down or rebooting. Defaults to 90s but I am impatient so I set this to 10s as anything on my system that takes longer than five seconds is broken, so a 10 second timeout is just fine.

If you are using a Pi 2 or older, set dtparam=watchdog=on in /boot/config.txt and reboot. This is enabled by default from the Raspberry Pi 3 onwards, so you can skip this step with recent models.

You don't need to run systemctl enable watchdog (that's for the old method mentioned above) but you will need to run systemctl daemon-reload (or reboot) after making these changes before they will take effect.

Answer 2

For the RaspberryPi4 it's more straightforward than for earlier software as much of the configuration scaffolding is already in place.

Edit /etc/systemd/system.conf adding the line

RuntimeWatchdogSec=15

then reload systemd's configuration with the command sudo systemctl daemon-reload.

Do not use values greater than 15 seconds, as that's the limit for the RPi4's countdown timer.

Optionally, if you want the watchdog timer to also detect systemd crashing then edit /boot/cmdline.txt to add to the existing line the new kernel parameter

bcm2835-wdt.nowayout=1

then reboot the system with the command sudo systemctl reboot.

Answer 3

Do NOT attempt to load ANY modules.

Add dtparam=watchdog=on to config.txt and Device Tree will load the module.

NOTE you also need to enable the watchdog service. See https://raspberrypi.stackexchange.com/a/68332/8697

Answer 4

Ok, after some testing it seems like the watchdog module is loaded by default. To check for yourself, see if /dev/watchdog exists.

This is the guide what worked for me.