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Old 09-08-2008, 01:48 PM   #1
linuxStudent11
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Question My FC9 install ISO is on an LVM partition (Why is this bad???)


I copied my linux.iso file to a random LVM partition on a second drive. Why does the installation manual say this is a no-no???

Grub seems to be very powerful. Why can't I just write an appropriate Grub stanza on my first drive to mount and start up that ISO??? Then I just continue to boot Grub off the first drive (that contains my old FC5) except I'll default the stanza to the one that boots FC9 off of yet-another LVM partition on my new drive.

I would do this right now except I don't know the filename to put in the grub script (on the old drive 0) to start up the installation/welcome screen ISO living in an LVM partition on drive 1.

Will someone please tell me what file to start running (using GRUB).
Otherwise, will someone please tell me why this can't work.

# I think the Grub stanza should kinda look like this:
title Installation
root (hd1,5)
kernel /vmlinuz-install root=/dev/VolGroup01/LogVol06-xtra rhgb quiet
initrd /initrd.img-install
# except that the file names are wrong (that's what I'm asking)

BTW: For conversation: the old drive is (hd0,1) where I boot from.
The new drive is (hd1,whatever). My FC9 ISO is alone in (hd1,5). I want to install onto (hd1,3).

# For that matter, why couldn't I just put the linux.iso just ANYWHERE on drive 0, say even right in /tmp and
Title Grub is very powerful
root (hd0,1)
kernel /vmlinuz-install root=/dev/VolGroup00/LogVol00/tmp rhgb quiet
initrd /initrd img-install
# or something like that

BTW: What's the difference between grub.conf and menu.lst????
 
Old 09-08-2008, 02:21 PM   #2
CRC123
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GRUB can load the initial ramdisk and kernel into memory fine; the problem happens once GRUB hands control over to the kernel. At this stage, the kernel is very small and does not have all the driver modules up and running it needs to read from the disk. The caveat here is that the modules are on the disk; the kernel can't read the disk until it loads the driver module for the disk/filesystem! (which came first, the chicken or the egg etc) The work around is the initrd(initial ramdisk); the kernel can read from memory just fine, so the initial ramdisk is loaded into memory as a 'virtual' filesystem. The initrd contains the necessary driver modules to read from the hard disk and some other stuff. Once the harddisk/filesystem drivers are loaded, the kernel can boot all the way up. If the initrd image is larger than available memory, the OS cannot boot and this is why the initrd image is kept as small as possible (for those people with only 64MB ram and smaller). LVM driver/modules are NOT included in the initrd image by default, so even if the kernel was able to load the initial ramdisk into memory, it still could not read the root filesystem to load the rest of the drivers. There are ways to force the inclusion of lvm drivers or any driver into the initrd image, but it is generally advised not to.
 
Old 09-08-2008, 04:12 PM   #3
linuxStudent11
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Thanks for this really informed answer.
So...what about the other possibility? Could I just hold the ISO at the root of my old drive? ...and then build the new FC9 onto one of the available LVM partitions?
BTW: The target partition for the new FC9 is /VolGroup01/LogVol00 which I think(?) is the first partition...if that matters. Probably not.

Last edited by linuxStudent11; 09-08-2008 at 04:23 PM. Reason: afterthoughts
 
Old 09-08-2008, 04:52 PM   #4
CRC123
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Quote:
Originally Posted by linuxStudent11 View Post
BTW: What's the difference between grub.conf and menu.lst????
menu.lst and grub.conf are normally linked; they are essentially the same file.

the 'linux.iso' file you're speaking of, is that an install image?

Do you not have a cd burner available?
 
Old 09-08-2008, 08:31 PM   #5
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Yes, linux.iso is the install image.
Yes, I have a burner...but it just seemed like an unnecessary extra step given all the capabilities of Grub...but I may be wrong on that. I guess I'm just lazy.
 
Old 09-09-2008, 12:05 PM   #6
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I guess that means the answer is "yes", I can load the installation ISO from /tmp using GRUB.
 
Old 09-09-2008, 12:11 PM   #7
CRC123
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It won't hurt anything to try. I've just always been under the impression that /boot and / shouldn't be on lvm. Worst case you burn a CD
 
Old 09-09-2008, 04:56 PM   #8
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I think I still need to specify the file inside the ISO on the GRUB kernel command. What is that file name?
I s'pose I can look it up. I'm still learning GRUB.
 
Old 09-09-2008, 05:03 PM   #9
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Hmmm...on second thought...as I think through what you said...it looks like both my kernel / partition AND my backup to / should NOT be on lvm. So that suggests I should delete the two lvm partitions and HOPE that leaves me uncommitted space on my hard-drive in which I can create and format PHYSICAL partitions. That should be simpler and less prone to bad things all-the-way-around.
So if I delete an lvm partition, does that just make it uncommitted? I'm hoping so.
 
Old 09-09-2008, 05:12 PM   #10
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LVM works something like this:

Volume Groups(VG's) live over top of Physical Volumes(PV's)
PV's Live over top of the disk (aka, they are a partition type)

Before you delete a PV, you need to remove it from the VG first, then it is uncommitted and you can remove it.

If you remove/delete a PV without removing it from the VG first, you will probably lose data.
 
Old 09-09-2008, 05:34 PM   #11
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I didn't read all of this, but grub can't deal with LVM's, hence RH based distros that tend to use LVM all put /boot on an ext3 partition.
 
Old 09-10-2008, 12:21 AM   #12
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Unhappy

Quote:
Originally Posted by CRC123 View Post
LVM works something like this:
Before you delete a PV, you need to remove it from the VG first, then it is uncommitted and you can remove it.
I'll try to explain myself again.

I have (almost) an entire disk (my "new" disk) that is LVM which I set up and started using before I understood the differences between logical and physical.

I built FC8 and successfully booted it on a LOGICAL VOLUME on the new disk. I think it is the first lv in the lvm group. I think that's why it works ok. BTW: Another GRUB lives on that volume.

I want to replace that FC8 with FC9. I think I need to delete one of the unused LV partitions, shrink the logical group, and recreate that partition as a PV. I'll use that (for now) as a mirroring backup.

Quote:
Originally Posted by billymayday View Post
I didn't read all of this, but grub can't deal with LVM's, hence RH based distros that tend to use LVM all put /boot on an ext3 partition.
Here's the fdisk -l

Disk /dev/hdb: 320.0 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/hdb1 * 1 25 200781 83 Linux
/dev/hdb2 26 38913 312367860 8e Linux LVM


Is the boot part of this just GRUB?????? Is THAT why this works ok?

How do I delete a partition and shrink the LV group?

I just wanna migrate gracefully to FC9. I'm tired of screwing with this.

AFTERTHOUGHT: I just looked at hdb1. It contains all the kernel and initrd stuff. It looks like this forms a sort of stub root that everything else is mounted onto. SO...64 million dollar question...how do I morph this into FC9.....ssiiiiiigggghhhhh.
 
Old 09-10-2008, 12:39 AM   #13
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Are you trying to boot off an ISO? I don't think this can work, since grub is not in the business of mounting ISOs (especially not ones it can't see in an LVM).

Is there some reason why you aren't just burning the ISO to a CD/DVD and install it that way like everyone else?
 
Old 09-10-2008, 01:18 AM   #14
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ok, I'll burn it.
My only dvd is on usb. I don't think this bios lets me boot from usb. (I could be wrong here.)

Just out of curiousity...what is an ISO and why is it so special? Can you point me to an faq on this?

And if I just burn the ISO onto the CD/DVD, how does a boot process (that looks for an MBR) find and use the ISO?
I guess the main problem here is that I don't understand. And anything I don't understand is untrustworthy.
I know that's probably arrogant. But it also tends to save my life (except when I get fired for asking too many questions.)
 
Old 09-10-2008, 01:33 AM   #15
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I don't know what ISO stands for, but it's a disk image, so when it's burnt to a CD/DVD, it isn't an ISO any more (it's a bunch of files on the disk, but formatted properly for booting - not a result you get if you just copy files to a CD/DVD).

Note that when you burn an ISO to disc, you need to specify that you are burning a disk image, other wise there will just be one file on the disk - the ISO.

So as you can see, ISOs aren't that special, it just makes creating a bootable CD/DVD far simpler.

Edit - happy to be corrected, but I suspect it's called an ISO because it's an ISO9660 filesystem.

Last edited by billymayday; 09-10-2008 at 01:35 AM.
 
  


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