Boot from external hard drive [USB]

tdcrooks · #1 3rd April 2009, 06:50 PM

Hey everyone,

I have an installation of CentOS on a hard drive for school, which works, but I wanted to work on it at home on my laptop.

I have an external hard drive enclosure that I use for backups, so I took my backup drive out, put the CentOS drive in, booted up my laptop, and chose boot from USB on the boot menu [after hitting F12].

It successfully goes to the CentOS splash screen, and starts booting up CentOS, but one or more services fail [one I know for sure was iptables] then it goes to my Fedora 10 login screen for some reason

Anyone have any ideas as to how I can boot up CentOS from my external drive successfully?

Much appreciated.

tdcrooks · #2 4th April 2009, 05:41 PM

No ideas anyone?

tsyshadow · #3 4th April 2009, 05:50 PM

The problem, I think, is that its loading the CentOS Kernal and initrd, but booting your Fedora 10 Partition. Check your grub configureation on your CentOS Drive, I think you'll find that its sent to boot to the wrong hard disk.

bruno.taglienti · #4 4th April 2009, 06:22 PM

Check the value of root=... in the kernel line of your grub.conf. This value must point to the root file system of your CentOS installation

tdcrooks · #5 4th April 2009, 06:50 PM

Hmmm you know what, I think that line has the same "default, non-renamed at installation" information for both my CentOS drive and my laptop's Fedora drive...

Here's my CentOS grub.conf

Code:

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/VolGroup00/LogVol00
#          initrd /initrd-version.img
#boot=/dev/hda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.18-92.el5)
	root (hd0,0)
	kernel /vmlinuz-2.6.18-92.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
	initrd /initrd-2.6.18-92.el5.img

And here's my fedora grub.conf

Code:

title Fedora (2.6.27.12-170.2.5.fc10.i686)
	root (hd0,0)
	kernel /vmlinuz-2.6.27.12-170.2.5.fc10.i686 ro root=/dev/VolGroup00/LogVol00 rhgb quiet vga=0x318
	initrd /initrd-2.6.27.12-170.2.5.fc10.i686.img

I'm willing to rename either of the lines that have this:

Code:

root=/dev/VolGroup00/LogVol00

That is, for either OS.

What's the safest way do this without killing the respective installation?

bruno.taglienti · #6 4th April 2009, 07:10 PM

It is clear that you use the same root file system for Fedora 10 and CentOS and this is wrong.
Try to understand what is the root CentOS partition and use it in the relevant line of
grub.conf

tdcrooks · #7 4th April 2009, 07:24 PM

Quote:

Originally Posted by bruno.taglienti

It is clear that you use the same root file system for Fedora 10 and CentOS and this is wrong.

Until yesterday the two drives in question never even came close to each other - my CentOS drive always remained at school. I think it's just that they happen to have the same logical volume names and this is causing some sort of confusion for my laptop.

This is strange since I would expect my laptop to ignore what it's own drives logical volumes are named if I'm choosing to boot from USB...

By the way though, this is just my understanding, if I'm wrong, correct me by all means.

bruno.taglienti · #8 4th April 2009, 08:49 PM

I am completely ignorant on LVM topics. In a non-LVM situation you can distinguish devices using
labels or UUID. Try to understand if the same (or analog) concepts can be applied on LVM

bruno.taglienti · #9 4th April 2009, 09:02 PM

vgdisplay -v should give UUID for all your LV.

Once you discover the UUID of the CentOS root fs, use root=UUID=....... in grub.conf instead of:
root=/dev/VolGroup00/LogVol00

UUID are unique, so the Fedora 10 and CentOS root fs must have different UUID

tdcrooks · #10 4th April 2009, 11:09 PM

Quote:

Originally Posted by bruno.taglienti

Once you discover the UUID of the CentOS root fs, use root=UUID=....... in grub.conf instead of: root=/dev/VolGroup00/LogVol00

Dude, typing this:

Code:

root=UUID=

causes kernel panic.

I modified what you said to say just this

Code:

UUID=

instead [ with the proper UUID following "UUID=" ], and THAT worked.

I'm so far able to boot up CentOS on a desktop computer with this method. I'm gonna try it through USB again now and let you know if it worked.