[sf-lug] UUID seems unique for each partition

Evan Klitzke eklitzke.lists at gmail.com
Tue Jan 16 18:38:44 PST 2007

On Tue, 2007-01-16 at 15:08 -0800, Jason Turner wrote:
> Hmmm, disk labels!  Perhaps that would work for me too, though I'm  
> not clear on how a label gets mapped(physically) to a partition?   
> Good info though.

I'm not sure, but I *think* the way that it works, is there is some
allocated space at a magic location at the beginning of the filesystem
that stores the UUID/label information. This also makes sense when you
realize that not all filesystems (only ext2/3 and swap AFAIK) support
labels. In grub you specify something like "root (hd0,5)" and then grub
boots using that device and whatever path the kernel is at. Grub doesn't
know anything about UUIDs/labels at all. The kernel sees that it has an
argument saying root=LABEL=... or root=UUID=... and the kernel has code
that lets it understand how to read and find a label/UUID, and it looks
at all the filesystems on your drive and figures out which one matches
the root= parameter you specified.

> BTW, Fedora Core 5 didn't have this problem(and I think now it may  
> have been using disk labels) but I forget.  Anyone with an FC5 LIVE  
> CD could check this.  Ubuntu 6.10 supposedly does things a bit  
> differently too, so if anyone running it could tell us...

I am using Fedora, and it uses labels by default. Ubuntu uses UUIDs (and
I don't think it applies labels to the filesystems unless you manually
did that). Functionally they're both very similar though.

> I had a few more questions around my fstab entries too(swap device / 
> UUID entry, Windows partition entry, SSHFS entry...) but I'll save  
> that for our next mtg or another thread.  It's been a steady stream  
> of lessons getting this to work.  And it sounds like I have much more  
> to learn.  Fun!

I'm glad you're having fun :-)

Evan Klitzke

More information about the sf-lug mailing list