I installed debian testing on an external usb drive. However, grub was installed on the main hard disk mbr. To correct this, I used grub legacy- copied its grub folder from another installation to /boot/ folder of external usb drive and corrected the menu.lst file. Then I booted from a live cd with grub legacy and at grub prompt gave commands: root (hd1,0); setup (hd1).

Now I have a well functioning debian testing installation on external usb drive. However, I am worried that grub installation will be altered when I run 'apt-get update' and 'apt-get upgrade' or 'apt-get dist-upgrade' commands. How can I prevent upgrade process from touching grub-legacy of my system? I want to use grub-legacy and not grub2. Thanks for your help.

I'm not familiar with the package names for grub-legacy. But if you installed it from a repo, you can set it's status to hold with:
This will prevent the package manager from updating the held-back packages during an update/upgrade.

If you need further help, please post the output of:
Hope it helps.

BTW: GRUB-legacy is no longer maintained either by Debian or the grub developers, so bugs and the like are no longer fixed. It's recommended that you upgrade to GRUB2 since it also provides enhanced features and filesystem support.

Thanks for your reply. The output of the command "dpkg --get-selections | grep grub" is:

is a GRUB2 package. Did you run this after booting from the USB drive? You can check the version of GRUB with (don't know if this works with GRUB-legacy):

I did not run grub2 after installation. As I mentioned earlier, I had manually copied grub folder (grub-legacy) to boot folder and adjusted the menu.lst file.

Do you think I can use "apt-get purge grub" and "apt-get install grub-legacy" to get proper installation of grub legacy on my system?

OK, so GRUB-legacy was not install from a package. There are two ways to block GRUB-legacy from being upgraded to GRUB2.

• Save the /boot/grub directory, purge the GRUB2 packages and the move the backed-up /boot/grub directory back to /boot/grub:
  Code:

  sudo cp -r /boot/grub /boot/grub_orig    # Backup the GRUB dir
  sudo apt-get purge grub-pc grub2-common    # Purge the GRUB2 packages
  sudo mv /boot/grub_orig /boot/grub    # Restore the original GRUB directory

  You may also have to redo the root (hd1,0); setup (hd1), but I'm not sure about this.
• The simpler way is to set the GRUB2 packages to hold status:
  Code:

  sudo su
  echo -e "grub-common hold\ngrub-pc hold\ngrub-pc-bin hold\ngrub2-common	hold" > dpkg --set-selections
  exit

  Code:

  dpkg --get-selections

  should now return:
  
  Code:

  grub-common					hold
  grub-pc						hold
  grub-pc-bin					hold
  grub2-common					hold

There is no grub-legacy package in the Wheezy (testing) repos. It's in the Squeeze repos. I'm not sure if it will install properly in Wheezy.

A big OOPS. My mistake, grub-legacy is in fact in the Wheezy repos. You can try and install it from there.
This should certainly fix it.

Thanks for your replies.

This I know that one does not need to repeat setup if just folder is moved in and out (as long as partition number remains same).

Do I need to purge "grub-pc grub2-common" or just "grub"?

Also, will installing grub-legacy reinstall grub on mbr also? Will it ask for any confirmation? Or I can just purge grub2 and leave grub-legacy as it is since it is working well.

You have to remove grub=pc and grub2-common. grub is a transitional package used to handle upgrades to GRUB2:
I suggested you use apt-get purge instead of apt-get remove because purge removes the packages plus their configuration files.

I tried it on my Wheezy installation in a VM and effed it up. After doing:
Checking the version of GRUB gave:
But on rebooting, I still got my GRUB2 boot screen.

Checking the /boot/grub directory still showed grub.cfg and other GRUB2 related files. There was no stage1 or stage2 etc files. I purged the grub-legacy package and deleted all GRUB2 related files and re-installed the grub-legacy package:
But now there was no /boot/grub directory. So grub-install gave:
I knew better but still decided to reboot since I saw grub-legacy files in /boot/grub. Now I'm at the grub rescue prompt. Ah well, serves me right. Now I need to get my Wheezy bootloader up but I have no idea what to do at the rescue prompt.

Will try though and let you know.

Edit: I think it's failing of my ext4 fs. As far as I can recall, grub-legacy did not support ext4 fs.

Thanks for your efforts. The best (and simplest) way to install grub-legacy is to copy grub folder from a working grub-legacy installation to your partition, boot to grub-legacy prompt and give commands: root (hdx,y) ; setup (hdx) or setup(hdx,y). It will install required stages to mbr of (hdx) or partition boot record of (hdx,y). Both x and y start from 0 in grub-legacy. Grub legacy supports ext4 partitions (I am using in on ext4 partitions).