[Solved] GRUB always puts me to command prompt

solamour · Last edited by solamour on Sun Sep 26, 2010 6:38 am; edited 1 time in total

I have a relatively old (several years old) PC that has 320GB IDE hard disk. I'm sure it might not be a good practice, but I like keeping things simple, so I have only 2 partitions.

BradN · Posted: Sat Sep 25, 2010 2:11 am Post subject:

As a debugging step, symlink /grub to /boot/grub.

If that makes it work, remove the symlink and try reinstalling grub to the mbr or partition (depending how you have it).

I always thought grub tried to read:
/boot/grub/menu.lst

- and not:
/grub/menu.lst

- just to seamlessly handle boot partition or no boot partition. In the case where there is a boot partition, /boot is symlinked to / so that grub can follow it and still find its stuff. But, it's possible that grub now checks the location when it's installed and alters its search path accordingly.

There really isn't anything to worry about with not having a boot partition in general, but it can cause minor headaches depending what filesystem you use. For example, reiserfs3.6, if uncleanly unmounted, will take many seconds to begin booting, as it seems grub re-checks the journal for every step it makes loading files.

If the /grub symlink doesn't make it work, double check that grub.conf is a symlink to menu.lst, as menu.lst is the file grub actually tries to read.

solamour · Posted: Sat Sep 25, 2010 5:53 pm Post subject:

I created a symlink "/grub" to "/boot/grub", but that didn't solve the problem.

NeddySeagoon · Posted: Sat Sep 25, 2010 5:58 pm Post subject:

solamour,

Post your grub.conf file and the output of

solamour · Posted: Sat Sep 25, 2010 6:28 pm Post subject:

Here they are. Once I enter "root (hd0,0)" and "kernel..." in GRUB's command prompt, I can boot the system.

krinn · Watchman Joined: 02 May 2003 Posts: 7470

i think it's more related to partitions type.

In case one you have / as ext4
In case two you have test with a /boot as ext2

Many people upgrade grub to newer version but always forget to upgrade the grub version INSIDE the mbr.
And grub1 wasn't design to support ext4, this was add by a patch.

So: redo your testing with a /boot partition, but made it ext4 this time instead of ext2, pretty sure your grub won't boot it too

If it work, you should redo the grub setup so newer grub version crush the old one in your mbr

NeddySeagoon · Posted: Sat Sep 25, 2010 7:06 pm Post subject:

solamour,

That all looks good. Comment out

Veldrin · Posted: Sat Sep 25, 2010 7:25 pm Post subject:

krinn · Watchman Joined: 02 May 2003 Posts: 7470

NeddySeagoon · Posted: Sat Sep 25, 2010 8:32 pm Post subject:

krinn,

A non ext4 grub in the MBR cannot read anything from an ext4 boot.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

krinn · Watchman Joined: 02 May 2003 Posts: 7470

This must be the solve then:
http://www.gnu.org/software/grub/manual/grub.html#GRUB-only-offers-a-rescue-shell

As it must have an old grub (or newer one) with a badly "set" that prevent grub from loading "normal" and so cannot find the grub.lst file

I was thinking how could this happen?
Well, answer might be that (or something else, but that's a good reason i think):

mount /boot (from hd0,1) to / (hd0,0)
ask grub install itself in mbr
grub now record it's default "set" = "prefix=(hd0,1)/grub" in your mbr of (hd0)

now unmount & erase the (hd0,1) as you only wish to use the / (hd0,0)
emerge grub = install grub files to /boot (but this boot is in hd0,0), but as you don't install grub in mbr again, prefix remain set as before

when booting, grub is still "set" to "prefix=(hd0,1)/grub where your prefix should now be (hd0,0)/grub

edit: for the op, i'm sometimes (nearly always) not clear, but you can temporaly correct it as they said in the link, and you were doing it when forcing root(hd0,0)...
To fix it, you must boot your gentoo
type grub
(now in grub menu)
root (hd0,0)
setup (hd0)
this will reinstall grub in your mbr, but this time grub should record prefix=(hd0,0)/grub
(well, if i'm right)

BradN · Posted: Sat Sep 25, 2010 11:57 pm Post subject:

You can do the installation commands from grub itself (at system boot) also, but it must be able to read its files from the hard drive (then again, it must be able to read its files from the hard drive to do anything). In fact, if you have problems installing it within gentoo (maybe if it gets the device order wrong with multiple hard drives), that's an option.

solamour · Posted: Sun Sep 26, 2010 6:38 am Post subject:

Whether the partition is ext2 or ext4 doesn't seem to matter, because
1) booting is OK when there is a separate boot partition (/dev/sda1) in ext4
2) the other machine with the original 60GB hard disk is also ext4 in a single partition.

"splashimage" doesn't seem like the cause of the problem, because even if I comment it out, the problem doesn't go away.

Veldrin:
"/etc/fstab" with 3 partitions ("/boot", "/", swap) was to verify whether creating a separate boot partition was effective or not. After I made sure having a separate boot partition solved the problem, I went back to 2 partitions ("/" and swap).

I vaguely remember the system booted OK with a single partition at one point in the past. Anyhow, I tried to shrink the partition to something smaller (about 20GB), but gparted was taking a very long time to finish it, because the system was pitifully underpowered (AMD Geode 500Mhz).

After several hours, I got tired of watching the endless progress bar, so I stopped the shrinking process despite of gparted's warning on possible corruption of file system if canceled in the middle. Just to ease my mind, I tried booting for the one last time.

And what do I know, the system booted properly. It complained about the file system not clean, but after fsck, everything worked as expected. No more GRUB's command prompt.

I think what's happening is that the system has some sort of a boundary, and if the files are stored outside that boundary, it can't read until Gentoo is fully up and running. Even though I canceled the shrinking process in the middle, the files in "/boot" were moved toward the front of the disk, and perhaps that's why now I'm able to boot. The problem might come back later when the boot files are pushed to the back of the disk.

Because it's working, I'm going to leave it as is for now. If you have any suggestions on how to prevent the problem from coming back, please share your thoughts. Thank you everyone for taking time to respond. I appreciate it.
__
sol

Randy Andy · Posted: Sun Sep 26, 2010 9:35 am Post subject:

@ BradN

you wrote:

NeddySeagoon · Posted: Sun Sep 26, 2010 11:03 am Post subject:

solamour,

Well caught!
Older machines, or rather older BIOSes do indeed have a boundary. So do modern systems. The difference is that with older systems the boundary lies inside the hard drive space.
Going back a few generations , its 137G, 33G ... all the way back to 528Mb, which is why a small /boot at the front of the drive became popular.
The race between BIOSs and hard drive sizes continues. The boundary today is at 144115TB. It will be a while before drives get that big.

What happened to you is that grub.conf was above the boundary and could not be read. Grub uses the BIOS for reading all the files needed to boot.
All your other boot files must have been below the bounday.

If you want the full story, read the Large Drive HOWTO on tldp.org
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

krinn · Watchman Joined: 02 May 2003 Posts: 7470