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Sometimes, when hdd feeling bad, your OS can’t start normaly.
And you are getting grub concole, like: grub >
The easiest way to boot your kernel:
1. check the list of drives
grub> ls
(hd0) (hd0,gpt2) (hd0,gpt1)
2. Check /boot folder on the drive (or another folder, depends from your server structure)
grub> ls (hd0,gpt1)/boot/
. .. grub initrd-2.6.32-ovz-el-alt88.M60P.1.img System.map-2.6.32-ovz-el-alt88.M60P.1 vmlinuz-2.6.32-ovz-el-alt88.M60P.1
3. Booting
grub> set root=(hd0,gpt1)
grub> linux /boot/vmlinuz-2.6.32-ovz-el-alt88.M60P.1 root=/dev/sda1
grub> initrd /boot/initrd-2.6.32-ovz-el-alt88.M60P.1.img
grub> boot

Another way is more complicated. And you should use it, if you got an error “grub unknown command linux”
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While installing some package via yum, you can receive the error “Package mysql.noarch.rpm is not signed”.
It means you are using not official repositary.
To solve this problem, just add --nogpgcheck
Example
yum install mysql --nogpgcheck

Sometimes its a big problem to install OS on hdd’s after hardware raid. Because hdd contains RAID metadata and OS can’t be installed.

To remove RAID metadata, do following:

dd if=/dev/zero of=/dev/sda bs=512 count=20 – removing first 20 sectors of the drive

then check number of sectors via command fdisk -s /dev/sda

dd if=/dev/zero of=/dev/sda seek=(number_of_sectors – 20) bs=1k – removing last 20 sectors of the drive

or

dd if=/dev/zero of=/dev/sda seek=$(( $(fdisk -s /dev/sda) -20)) bs=1k

Do this on all drives with RAID metadata