[CentOS] Corrupt mbr and disk directory map
Billy Davis
bdavis at cds-corp.com
Thu Jan 5 20:21:32 UTC 2012
On 1/5/2012 11:20 AM, m.roth at 5-cent.us wrote:
> Billy Davis wrote:
>> We are running Centos 5.6. All was fine until yesterday. I attempted
>> to tar a 14KB work file to a USB floppy (/dev/sdb) for transport to
>> another server. Unfortunately, I keyed in 'tar cvf /dev/sda filename'
>> instead of 'tar cvf /dev/sdb filename'. /dev/sda is our main
>> (boot/root/apps) scsi hard drive. I realized my mistake, but it was
>> too late. The system is still powered up and running, but I am sure
>> that I have overlaid (and trashed) the mbr and the disk directory map.
> <snip>
>> I suspect that when I power the system down, it will not reboot. I can
> You have that right.
>
>> reinstall mbr and grub, but I don't have the original partition table
>> start/end values. Since the system is still running, it seems that the
>> partition table must still be available to it from somewhere.
>>
>> Is there any way to easily restore the partition table?
> Easily? No (other than the grub-install /dev/sda part).
>
> Sorry about your problem, but I appreciate the question: it led me to
> <http://www.cromwell-intl.com/unix/linux-kernel-details.html>, a fair bit
> of which was quite familiar, and other bits weren't. For example, cat
> /proc/partitions might give you a serious bit of the information you're
> looking for.
>
> Hope that helps.
>
> mark
>
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Thanks Mark. The cat command provided the lost partition information.
I used that information with fdisk to restore the partition map. The
fdisk partition map is now identical to the cat partition information.
Next, I reinstalled grub. All seems normal now, at least until I
shutdown and reboot. I'll wait until the weekend to do that, just in
case I still have to do a disk restore for some reason.
Thanks again for your input.
Billy
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