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Old 09-16-2010, 09:41 AM   #1
paul1149
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Error 21 and GRUB logic


Hi,

I'm new to Linux and just installed PCLinuxOS to an external USB drive off a Win7 machine.

When I installed Linux, I placed GRUB on the main Windows drive. I think that was a mistake, because now I discover that even with Windows specced as the default, if the external USB drive is not available, GRUB faults out with Error 21, which research shows is "drive not available", and I can't boot to anything.

The logic of that escapes me. Why brick an entire system because one partition is not available?

In any case, I'm looking for a solution. I think I need to promote the USB drive's BIOS boot device order and place GRUB out on it, where it won't be missed if the drive is unavailable.

My three questions:
1. Is that correct?
2. I suppose this means a reinstall of Linux in order to place GRUB on the USB drive?
3. How do I cleanse the C: drive of the existing GRUB?
Thanks much,
Paul
 
Old 09-16-2010, 10:18 AM   #2
yancek
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It seems you placed Grub stage1 file in the master boot record on your internal hard drive. Since the mbr hass room for only 512 bytes, it obviously can't contain all Grub files. Most of the Grub files are on the partition on the external drive which is why you cannot boot without the external drive. Yes, you should have installed Grub stage1 to the mbr of the external drive.

You don't need to reinstall PCLinux, just reinstall Grub. After that, you use your windows CD to overwrite the mbr on the internal. For specific advice, we would need your partition information which you can get by logging in to PCLinux, opening a terminal and running the command: fdisk -l (lower case Letter L in the command). Post it here.

Here's a link to a tutorial on Grub:
http://www.dedoimedo.com/computers/grub.html

Link to download Recovery disk for win 7 if you don't have one:

http://neosmart.net/blog/2008/window...disc-download/

A link on recovering the bootloader. It says vista but win 7 uses the same bootloader so process should be the same.

http://neosmart.net/wiki/display/EBC...r+from+the+DVD

A minimal amount of reading on Grub prior to the install would have saved you a lot of trouble.
 
Old 09-16-2010, 07:42 PM   #3
paul1149
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Thank you, yancek, for a very comprehensive reply. I have read up on GRUB until I was totally frustrated, and I finally tried one of the simple install command lines. It said it worked, but later I found that the graphics and the disk info had not been registered along with the Stage1 loader. Fail.

I'm certain someone competent could have surgically corrected the problem within five minutes. I opted to reinstall PCLinux, losing a couple of hours of setup time I had invested. So it goes.

On the Windows side, the Win7 Recovery Disk routines did nothing for the MBR, which is exceedingly lame, but I found the console command to use. For subsequent viewers here, it's
bootsect /nt60 c: /mbr
where C is the drive with the mbr in need of repair, and it works effortlessly.

Perhaps you're correct about a minimal amount of reading being able to prevent this mess, but

a) I think a minimal amount of contextual help during the installation would be most appropriate; there was none. A simple paragraph concerning file location ramifications to a multiboot situation would have been most welcome. As it was, merely cancelling out of a sub-dialog caused the entire GRUB routine to terminate on my first time through, and I had no idea for a while if anything I had done had succeeded.

b) the subsequent GRUB reading I have done only took me deeper into the abyss of a problem I knew had to be simple at its core. I frankly feel that a lot more can be done to make this system user-friendly to newbies and those not super technically adept; and that doing so would increase Linux's appeal exponentially.

Thanks again for your conceptual help on this. It gave me the overview to see where I needed to go. Much appreciated.

Paul
 
Old 09-16-2010, 08:16 PM   #4
syg00
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I feel your pain, but in this case the problem is with the distro (PCLinux in this case) *not* grub. Several distros inflict this sort of thing on (new) users - principally those trying to to make everything "easy" and consequently not telling the user what's happening.
Or not telling the truth.
Trying too hard to be Windows look-alikes.

The grub doco can best be described as sparse - grub2 is probably worse.
 
Old 09-16-2010, 08:18 PM   #5
yancek
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The problem you had is pretty common and new users not knowing that the majority of the Grub bootloader files are on the root partition where Linux is installed and are needed to boot is the source of the problem.

You do get a choice as to where to install the bootloader which is something you do not get on a windows install. Just overwrites everything.

Quote:
I frankly feel that a lot more can be done to make this system user-friendly to newbies and those not super technically adept; and that doing so would increase Linux's appeal exponentially.
Agree with this comment. There are numerous tutorials on-line for some of the major distributions (the Ubuntu derivatives particularly) but I think having some detailed tutorial link on an install CD would be useful. I did this in a very simple fashion for Linux Mint and a couple of small distributions but that was more or less to see what I could do and I lost interest in it after a while.

I'm always happy when anything works. I like the freedom and the choices with Linux and see that as both its major advantage and major disadvantage, disadvantage for recruiting new users particularly.

Good luck and enjoy your Linux!
 
  


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