How to restore grub via Hetzner's Rescue systems?

Question

Debian

I will describe the situation: once upon a time there was a server (from Hetzner) and it worked remarkably well under debain 6
And now, after more than 3 years, I wanted to update it. Decided done. apt-get update, apt-get upgrade. During the update, a warning popped up in the blue window that grub was updated and changes needed to be made, but since I was not sure, I checked the boxes - leave it as it is. However, a vague suspicion crept in that after a reboot it might not take off. Therefore, the necessary data was transferred and rebooted.
As expected, the server did not boot. It would seem that everything is simple - booted into the Rescue system, mounted the disk, did grub-install, update-grub - wrote that everything is ok. But after the reboot, everything is also not available. And now I'm sitting here thinking that I'm doing it wrong.
Yes, there is nothing critical - I transferred everything that was needed to a new server in advance, but in principle I want to understand the situation. Yes, there is a software raid on the server. Therefore, I mounted /dev/md2 accordingly, since the /dev/sda and sdb disks themselves naturally do not want to be mounted

Answer 1

He asked, he answered. Maybe someone will come in handy.
For the case if you have software-raid and need to restore grub via Rescue, then:
ls /dev/md* //see what you have collected in the raid
mount /dev/md2 /mnt - mount the one I needed, it was md2
further chroot in mounted partition and unmount system resue files
mount --bind /dev /mnt/dev/; mount --bind /proc /mnt/proc/; mount --bind /sys /mnt/sys/
chroot /mnt
mount -a
And now grub-install /dev/sda and update-grub - this is exactly what could not be done immediately after booting into the rescue system
After reboot everything is ok