I went from happy to despaired in the last hour. I tried to access my Unraid server from my file manager, but got an error. I figured it was something harmless, so I went to the GUI which didn't work either (HTTP ERROR 500).
The Docker stuff worked, Plex ran, everything seemed fine, just a scratch, nothing serious.
Googling I found that probably I should ssh into Unraid and do /etc/rc.d/rc.php-fpm restart 

ssh did not work, so I went to the Unraid computer itself, logged in and did the above. No success, and then I saw that there was no space left on device.
I did df and found that rootfs was full, after reading in here https://forums.unraid.net/topic/114338-serious-problem-with-rootfs-full-and-no-space-left-on-device/ I confidentially restarted.
And nothing happened ever since. The computer starts and then gets stuck somewhere, but there is no console, nothing can be seen on the screen during startup (apart from the motherboard logo) and I cannot ping the computer.
It feels dead and honestly I really have no idea where to start. 
Of course I did not have the good sense to save any logs before restarting as it did not seem like the deadly problem it turned out to be.
So can you suggest any steps for me?

Thanks in advance, highly appreciated!!

Do you have a current flash backup? 

2 minutes ago, Swisshet said:

nothing can be seen on the screen during startup (apart from the motherboard logo)

You don't get the Unraid boot menu? 

54 minutes ago, trurl said:

Do you have a current flash backup? 

Unfortunately, it depends on your definition of "current". I have a file ds9-flash-backup-20241230-1326.zip where "ds9" is the computer name. I know I am an idiot. 

 

52 minutes ago, trurl said:

You don't get the Unraid boot menu? 

No, but I am not sure what you mean with "boot menu". Usually, when the computer is started it will start into some console - but that doesn't seem a boot menu to me.

Try recreating the flash drive, first backup the current one, then recreate it using the USB tool, confirm the flash drive boots with the stock install, and if yes, restore only the /config folder from the backup overwriting any existing files.

Good morning (sorry for the silence, European time zone  ) and thanks again to all of you.

If you don't mind just a few questions to be very sure about what I should do. I know all this might sound a bit clueless, but then I might actually be a bit clueless - but also I feel I better ask before doing some permanent damage... 😬:

1. "backup the current one"
   I assume you mean taking the current one, plug it into another computer and copy all the files into some backup directory - and NOT doing a "dd" copy to another stick? Ist that correct
2. "then recreate it using the USB tool"
   That would be the USB Creator as if I was to setup a completely new Unraid server, right? 
3. My Unraid might still be on 6.12.13 - I would guess that I have to use the same version in the recovery setup?
4. "confirm the flash drive boots with the stock install"
   Do I do that on my Unraid machine or is that not safe and I better try it on some old computer?

You just need to copy the /config folder

Yes

You can use the current one

On the server.

1 hour ago, JorgeB said:

You can use the current one

I know you must assume that I am dense, again my apologies, but do you mean

a) I can use the current Unraid 6 version (like 6.12.15) with the USB Creator or 

b) I should use the current (i.e. latest) Unraid 7 version?

- - -

My assumption that I should use Unraid 6(.12.15), because switching to Unraid 7 is a more complicated thing to do and probably wouldn't work. Is that correct?

Thanks a lot!

Also, having looked at the USB-stick, I note that most files do not seem to have been changed recently, so I am still at a loss about what went wrong.

You could use either, but probably best to stick with 6.12.15 for now.

 

 

So while preparing to write on that stick I figured I could try if it starts on some other computer. So I put it into an old NUC and it started without issue.

Hm. So now I know that I am on Unraid 6.12.8 (ahem), but I also wonder whether the problem is somewhere else. Before I shut down the Unraid server it was working, but then did not start any more. But the stick seems not to be the problem - I am quite at a loss but I guess I'll go forward with putting the new system on the stick.

But could it be something banal (and really improbable) like the USB port not working? 
I'll try the old stick in another port, just to be on the safe side.

Post a photo showing where the booting gets stuck.

OK, so I now tried the stick in another USB port and everything works like a charm. 
To me, as I wrote, it seemed highly improbably that this could be the problem - but there you go, I guess this was it. 
But to both of you, @JorgeB and @trurl, my heartfelt thanks! The only thing that is worse than having an unsurmountable computer problem is having an unsurmountable computer problem and being alone. And your help and readiness to help further was invaluable!

One last note, though, in case someone else runs into the same issue:
I think the underlying problem never was Unraid but the "Fast Boot" option on my MSI motherboard (per this link).
After writing the above I figured I should upgrade to at least the latest 6.12. version of Unraid, but then I had the same issue where it wouldn't start, not even into the boot menu.
So maybe it's not the USB port (it was pure luck that changing the port worked), or it's two issues combined.
However, 6.12.15 is up and running now.