Linux – How to disable a watchdog, once it has been enabled

linuxwatchdog

I created a watchdog daemon application with a time interval of 30 seconds; for every 5 seconds, I am trying to hit the watchdog counter, and it's working fine. If I kill this daemon process it shows the following:

mxc_wdt: Unexpected close, not stopping!

Then, my device gets reset after my time interval goes to zero (i.e.,hardware counter count down to zero).

I even configured CONFIG_WATCHDOG_NOWAYOUT=N in kernel.

Is there any process to disable this watchdog functionality at user bash prompt? I observed disable not supported by this chip in kernel mxc_wdt_disable function.

Best Answer

Normally to shut down the watchdog driver you have to write a 'V' character to /dev/watchdog which you could do from a root bash prompt just with:

echo 'V' > /dev/watchdog

However, before you try to create your own watchdog driver take a look at the existing Linux watchdog daemon to see if it can do the job. A good start is my page here: http://www.sat.dundee.ac.uk/~psc/watchdog/Linux-Watchdog.html

Q3: What do the results of `grep -i nmi /proc/interrupts` mean?

It becomes clearer if you see the headings of the columns:

$ cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3             
NMI:         24         18         21         18   Non-maskable interrupts

This command displays statistics about the interrupts per CPU.

Q2: What's the advantage of disabling nmi_watchdog?

The nmi_watchdog can, under some circumstances, generate a high number of NMI interrupts (i.e. when using local APIC and you have high system load). A high number of interrupts may slow down your system.

Q1: What could happen if I disable nmi_watchdog permanently?

Imagine your system locks up. There's 2 possibilities now:
1) You have a hardware NMI button (some servers do). Push it, then the kernel (if properly configured) dumps a trace to console and reboots.
2) Your kernel reaches a halting state that can't be interrupted by any other method. In this case, the watchdog can reboot the machine.

Ubuntu – USB ports keep resetting on Linux

I had the same issue, my dmesg was full with this messages, and could not unmount nor suspend the computer:

[ 4095.313680] usb usb4-port5: Cannot enable. Maybe the USB cable is bad?
[ 4099.301425] usb usb4-port5: Cannot enable. Maybe the USB cable is bad?
[ 4103.293161] usb usb4-port5: Cannot enable. Maybe the USB cable is bad?

I discovered it happens when keep a long time without unplugging the USB devices. Maybe the controller on some device goes erratic after staying so much time on, and going trough so many suspends and it is sending bad signals.

I discovered this fixes the problem:

unplug all your USB devices;

power off your computer and power off also the button which comes with the PSU (Power supply unit) because otherwise the PSU will still give juice to the motherboard and will still power the USB controllers on the device attached to it.

And of course sometimes can also be a bad cable. See here: https://askubuntu.com/a/348799/82315

Best Answer

Related Solutions

Linux – Should I disable NMI watchdog permanently or not

Q3: What do the results of grep -i nmi /proc/interrupts mean?

Q2: What's the advantage of disabling nmi_watchdog?

Q1: What could happen if I disable nmi_watchdog permanently?

Ubuntu – USB ports keep resetting on Linux

Related Question

Q3: What do the results of `grep -i nmi /proc/interrupts` mean?