My friend has a server hosted in SoYouStart, and suddenly the server went down and nobody knew why. He asked my helped to bring it back online.
We tried to boot into recovery mode from the console, and we were able to login using the credentials sent by them. We were also able to download all the files as a backup. However once we boot normally, the server was still not reachable.
Suspecting its a bootloader issue, I tried to re install grub, and it worked. This is how I fixed after logging in in the rescue mode.
$ fdisk -l (to find the names of physical drives, something like “/dev/sdxy″ – where x is the drive and y is the root partition.Ours was a RAID setup, so /boot was on /dev/md1, / was on /dev/md2)
$ mount /dev/md2 /mnt (Mount the root partition)
$ mount –bind /dev /mnt/dev
$ mount –bind /proc /mnt/proc
$ mount –bind /sys /mnt/sys
$ chroot /mnt (This will change the root of executables to your your drive that won’t boot)
$ mount /dev/md1 /boot (Mount the boot partition. If /boot is not a separate partition, no need to do this step)
$ grub2-mkconfig -o /boot/grub2/grub.cfg
$ grub2-install /dev/sda (/dev/sda and /dev/sdb were the physical disks, not partitions used in the RAID setup. If it is not a RAID, the you should use the disk where /boot is installed)
$ grub2-install /dev/sdb
Ctrl+D (to exit out of chroot)
$ umount /mnt/dev
$ umount /mnt/proc
$ umount /mnt/sys
$ umount /boot
$ umount /mnt
We finally managed to bring up the server which was down for two weeks. Felt so proud of it.