I went through this experience recently. First of all, don’t panic! I panicked, and because of this, I made a mistake: I didn’t wait long enough for it to come online. Had I waited up to 60 minutes, it would probably have come online (see reason below). The story:
I had broken packages on my Ubuntu 10.04 server and decided to fix them by
apt-get update apt-get upgrade
While updating, I noticed that the package grub-pc also was upgraded, apparently a new bootloader (or bootloader configuration) was installed. This made me feel uncomfortable, since I didn’t know if the server would reboot after this upgrade. So, because of the saying “The devil you know is better than the devil you don’t know” (and a desire to sleep peacefully at night!) I decided to reboot the server and see what would happen. To my big dismay, it did not come online. SSH connections failed with “Port 22: Connection refused” .
I panicked and asked the Hetzner Support (which is very responsive and supportive btw!) to install a LARA Remote Console so that I could see the text output of the booting screen. After some regular startup text, the screen became blank. I panicked even more and took immediate steps to move all data to a new server. It took me 6 hours to complete the most important parts, and another full week of restless work to finish it. We will see that it was not necessary.
Most regular servers at the Hetzner data center are running Software RAID. It seems that after a reboot (especially if you send a Hardware Reset) the OS needs some time to re-sync or check the file system. I am not sure what caused the delay in my case. Re-syncing the entire RAID array can take up to 1-2 hours, depending on your hardware and disc space.
So, wait at least 1 hour for it to come online, especially after a hardware reset! When you activate Hetzner’s Rescue system (which is very good btw!) it will stay active for a minimum of 1 hour, so your server will be down for 1 hour at least, in any event. So you are not losing much by waiting a bit longer.
Now, in my case, I assumed that Grub2 was broken. So I activated the Hetzner Rescue System, booted into it, and reinstalled Grub2. I have found the following method here and it worked for me. First you have to mount the regular RAID filesystem under /mnt :
mount /dev/md2 /mnt mount /dev/md1 /mnt/boot mount -t dev -o bind /dev /mnt/dev mount -t proc -o bind /proc /mnt/proc mount -t sys -o bind /sys /mnt/sys chroot /mnt
At this point, you are in your regular root directory. To reinstall Grub2 the Debian Way, I did:
apt-get install --reinstall grub-pc
To make really sure, I reconfigured the package:
It will ask you where to install the bootloader. I selected:
[*] /dev/sda [*] /dev/sdb
No errors were reported. I rebooted again and it did not come online immediately, for the reasons previously mentioned. I waited long enough (in my case, 15 minutes) and it did come online. So, rule number one is: Don’t panic!