Greetings @jose_au_zone,
You are on the right track but the method is a bit different. We store our config files for systemd here:
sudo ls /usr/lib/systemd/system.conf.d
00-systemd-conf.conf 10-systemd-conf.conf
Inside the file 10-systemd-conf.conf is where we set the systemd-watchdog usage:
[Manager]
# Change CtrlAltDelBurstAction from default of `reboot-force` to `none`.
# Disable the immediate reboot which occurs when Ctrl+Alt+Del is pressed more
# than 7 times per 2s
# https://www.freedesktop.org/software/systemd/man/systemd.html#SIGINT
CtrlAltDelBurstAction=none
DefaultEnvironment="MACHINE=verdin-imx8mp"
RuntimeWatchdogSec=30s
Unfortunately this is in a read-only part of the filesystem so you can’t trivially modify this file to remove the RuntimeWatchdogSec=30s line. However you can create another similar file to overwrite this. Create the following file /etc/systemd/system.conf.d/10-systemd-conf.conf. As for the contents it’s the exact same as the first file minus the last line regarding the watchdog. This file in /etc should now overwrite the one in /usr/lib. After a quick reboot you should see that the watchdog is not used by systemd anymore:
verdin-imx8mp-06849059:~$ dmesg | grep watchdog
[ 1.323643] imx2-wdt 30280000.watchdog: timeout 60 sec (nowayout=0)
verdin-imx8mp-06849059:~$ sudo fuser -v /dev/watchdog
verdin-imx8mp-06849059:~$
Please give this a try and see if you can now use the watchdog for your needs.
Best Regards,
Jeremias