[SOLVED] Installing GRUB in MBR

mangya · 07-18-2015, 07:11 AM

Hello

I'm trying to install grub to a broken mbr. This is the part of my learning and the linux distro is CentOS 7 minimal running in virtualbox.

I want to try this in various ways.

First I booted from CentOS DVD's Rescue mode and installed mbr successfully by grub2-install command.

Then, I tried through SystemRescueCD. Installed GRUB perfectly. Following are the steps:

Code:

% mkdir linux

% vgchange -a y VolGroup

% mount /dev/mapper/VolGroup-root linux
% mount /dev/sda1 linux/boot

% mount -o bind /proc linux/proc
% mount -o bind /dev linux/dev
% mount -o bind /sys linux/sys

% chroot linux /bin/bash

# grub2-install /dev/sda
Installing for i386-pc platform.
Installation finished. No error reported

However, when I tried this in Knoppix Rescue DVD, even though every step is exactly same, I'm getting error at chroot

Code:

# mkdir linux

# vgchange -a y VolGroup

# mount /dev/mapper/VolGroup-root linux
# mount /dev/sda1 linux/boot

# mount -o bind /proc linux/proc
# mount -o bind /dev linux/dev
# mount -o bind /sys linux/sys

# chroot linux /bin/bash
chroot: failed to run command `/bin/bash': Exec format error

# chroot linux /bin/sh
chroot: failed to run command `/bin/sh': Exec format error

# chroot linux
chroot: failed to run command `/bin/bash': Exec format error

What I'm doing wrong? Please help.

Thanks

Aia · 07-18-2015, 10:51 AM

Quote:

The error Exec format error means that the binary being executed is made for a different architecture than the environment currently booted. It usually occurs when the system has been booted on a 32-bit system when a 64-bit environment is trying to load.

Source

mangya · 07-18-2015, 11:16 AM

@Aia Thanks man! it was really very helpful. Booted Knoppix with boot-code knoppix64 and it worked flawlessly.

Thanks

Shadow_7 · 07-18-2015, 11:16 AM

You need to be running a 64 bit kernel to chroot into a 64 bit linux. You could use grub on a USB stick and boot the install on the device on bare metal instead of doing the chroot. If grub is on that device but not the MBR, you can chainload the other grub's configuration in grub. And other options.

GRUB> configfile (hd0,1)/boot/grub/grub.cfg

where the (hd0,1) is the device and partition for the other grub. As hinted to from GRUB> ls

mangya · 07-18-2015, 11:36 AM

Quote:

Originally Posted by Shadow_7

You need to be running a 64 bit kernel to chroot into a 64 bit linux. You could use grub on a USB stick and boot the install on the device on bare metal instead of doing the chroot. If grub is on that device but not the MBR, you can chainload the other grub's configuration in grub. And other options.

GRUB> configfile (hd0,1)/boot/grub/grub.cfg

where the (hd0,1) is the device and partition for the other grub. As hinted to from GRUB> ls

Thanks for your reply. But till now, I am trying to repair Grub at stage 1. So I don't even get GRUB> prompt. I am getting 'No bootable medium found' error.

I'm deliberately removing mbr by

Code:

dd if=/dev/zero of=/dev/sda bs=446 count=1

I think I can use your solution at grub's stage 2 error. I'm still learning grub.

Anyway, thanks.

Shadow_7 · 07-18-2015, 06:00 PM

Grub is just a boot loader, which can exist on ANY bootable medium. You can select which drive to boot as primary in most BIOS/UEFI implementations. And you can boot USB devices on most x86 machines since 2006. A grub implentation can exist on said USB mediums. If a linux also exists on said medium you can boot the linux on usb, run update-grub and boot the usb again and select the thing to boot from grubs menu (the grub on the USB drive). Mostly the same as your chroot method. Except you actually boot the distro instead of using chroot. Back in the day you'd have to use grub on a cdrom to boot from usb for machines that didn't support booting usb. Many means to an end.