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I own a Pi4 (4GB), and I'm having some issues. The pi crashes with no apparent reason.

By crashes I mean it becomes unreacheable via ssh, PiHole and HomeAssistant that are running on it become unaccessible, and pugging in a monitor just gives "No signal - check cable". The only thing that keeps running is the 5V fan on it.

I understand that the answer should be in /var/log/kern.log but I don't find anything of notice in there at all.

What do I do to troubleshoot this?

Some things I found googling:

  • Power supply: I am using an official Pi4 5.1V 3A power supply.
  • Too many reads to low quality SD card: 64Gb samsung high quality sd card, and only pihole and HomeAssistant running.

I don't want to blindly replace parts, so what next? Rebooting makes it work just fine, but it crashes again at about the same time every day, in the morning.

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  • You need to collect data. Personally if it was crashing at the same time each day I would start by asking why at that time. I can't see that the Pi is relevant to the question or solution. – joan Oct 29 '20 at 11:43
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In my experience the best chance to get error logs from a crashing Pi is over a serial console. You need a system capable of logging the messages (e.g. a laptop with a USB to UART converter running Putty) connected at the time of the crash. A command which continuously prints log messages to the terminal (dmesg -w, logread -f, etc.) must be started in the serial console before the crash.

Crashes happening at the same time every day are likely due to cron or a similar scheduler. If your system crashes whey you run run-parts /etc/cron.daily, that's where the problem is. Another source of scheduled executions are the [Timer] units of systemd.

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There are hundreds of possible Reasons that can cause this behaviour. Some things that you should check for:

  • what do you do when the Pi crashes? (for example are you connecting something to the GPIO's?)

  • Connect the Fan to external 5V power source to exclude power shortage caused through the fan. Is the fan correct connected? Usually the Power over the GPIOs is quite limited and there are Fans that pull way more than the GPIOs can deliever.

  • Check what is connected to the USB-Ports. Disconnect everything and check if the Pi continues crashing. If no crashes appear continue with adding one USB-device after another. Also disconnect the HDMI.

  • Are the Pi's LEDs flashing? and which one are flashing? in the Pi's manual you can see what the LEDs and their behaviour mean. Quite useful for evaluating your problem.

  • have you tested another SD card? maybe your card is corrupt

  • what programms are running on the Pi? maybe there is something running that causes the crash

  • maybe you loose connection because of your router? is your pi also loosing connection when connected via LAN? how are you providing ip adress (via DHCP or fixed IP?). i made the experience that when Pi looses connection caused by the router it sometimes has difficulties to connect again to network.

  • as other users have written you can check with dmesg for the sys log. but if your pi crashes cause of a powerissue it may wont be able to catch this event.

  • googleing your PiHole showed me this: https://discourse.pi-hole.net/t/pihole-crashes-daily/33952/3 maybe it is a common problem with pihole

  • pls report back if it doesnt help and if any advice helped you pls tell us which one. thanks

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