[SATLUG] Grub hell

Borries Demeler demeler at biochem.uthscsa.edu
Fri Nov 20 18:25:31 CST 2015


I was wondering if we have some grub experts here who could help me out.
Here is the issue:

/dev/sda1: large gpt raid array on sata raid controller, ext4
/dev/sdb: large gpt raid array on sata raid controller, ext4
/dev/sdb1: 500 MB /boot partition, ext4
/dev/sdb2: several TB of diskspace, ext4, mounted on /

Onto this system, I installed from scratch Centos 6.7. I selected /dev/sdb1 
partition for the boot loader.

rebooted. The system would hang and could never find the boot loader,
even though it was installed using the CentOS installation disk.
So I thought, maybe it cannot deal with a gpt partition table, and
decided to remove one of the disks from the large /dev/sdb RAID5 array 
and use it as a single disk for the system. Now I have:

/dev/sda1: large gpt raid array on sata raid controller, ext4
/dev/sdb: single 1.5 disk with msdos partition table on sata raid controller
/dev/sdb1: 500 MB /boot partition, ext4
/dev/sdb2: 1.4 TB / partition, ext4
/dev/sdc1: large gpt raid array on sata raid controller, ext4

Onto this system, I installed from scratch Centos 6.7. I selected /dev/sdb1 
partition for the boot loader.

rebooted. Same problem, the system would hang before ever finding the
boot loader, even though the bios was pointing to the correct raid controller
with the single /dev/sdb drive in it.

So I reboot using the CentOS rescue disk. CentOS finds the previous installation
and mounts it under /mnt/sysimage. I chroot into it and fixed grub like this:

grub> find /grub/stage1
(hd1,0)
grub> root (hd1,0)
grub> setup (hd1)

all seems to go well. I reboot, and voila, now the system sees my bootloader!
However, when I try to load the kernel, I get:

Error 15: File not found

so I drop back into the command line and run the same commands. Now I get:

grub> find /grub/stage1
(hd0,0)  <-- note the first "zero"
grub> root (hd0,0)
grub> setup (hd0)

Again, all seems to go well, but rebooting gives me the same problem as before
(Error 15).

Then I tried two more things, all the same to no avail, error message stays the same:

grub> find /grub/stage1
(hd0,0)  
grub> root (hd0,0) /dev/sda
grub> setup (hd0)
(no error on write, but error 15 when trying to load kernel file)

and also tried:

grub> find /grub/stage1
(hd0,0)  
grub> root (hd0,0) /dev/sdb
grub> setup (hd0)
(no error on write, but error 15 when trying to load kernel file)

I am at my wits end, what am I missing here? Why can't the CentOS installer
not even manage to install a grub boot loader correctly???

I do not want the loader on /dev/sda since this array may be removed at some point.
If you managed to follow all of this and have some suggestion I'd be more than
happy to try it :)

Thanks! -Borries


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