Why no UUID's?

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Why no UUID's?

Postby plowna on Fri Sep 26, 2008 9:56 pm

I haven't specifically run into the problem of UUID's (am using Elyssa R1). However, recompiling the kernel I've had issues because I've forgotten to load/install the libata driver (Drives are detected as /dev/hd* instead of /dev/sd*, breaking menu.lst & fstab).

Querying in the ubuntu forums, I was told I should be using UUID's. Curiously, here though it is actively discouraged and Elyssa doesn't specifically seem to use it.

I understand that UUID's may change as a result of changes to the partition/drive/size/whatever. Isn't there a way to re-calculate the uuid? I mean, outside of linuxmint (say for example with a rescue cd or in windows or otherwise), there's only a finite number of ways you can change a partition. Is it not possible to build in a recalculation of the UUID into the programs that change partitions?

I guess my question at the heart of it is, why doesn't linuxmint use UUID's when ubuntu does? How does ubuntu get around things when UUID's change? Could linuxmint do the same?
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Re: Why no UUID's?

Postby miket on Sat Sep 27, 2008 5:18 am

Hi !

plowna wrote:I haven't specifically run into the problem of UUID's (am using Elyssa R1). However, recompiling the kernel I've had issues because I've forgotten to load/install the libata driver (Drives are detected as /dev/hd* instead of /dev/sd*, breaking menu.lst & fstab).

Querying in the ubuntu forums, I was told I should be using UUID's. Curiously, here though it is actively discouraged and Elyssa doesn't specifically seem to use it.

I understand that UUID's may change as a result of changes to the partition/drive/size/whatever. Isn't there a way to re-calculate the uuid? I mean, outside of linuxmint (say for example with a rescue cd or in windows or otherwise), there's only a finite number of ways you can change a partition. Is it not possible to build in a recalculation of the UUID into the programs that change partitions?

I guess my question at the heart of it is, why doesn't linuxmint use UUID's when ubuntu does? How does ubuntu get around things when UUID's change? Could linuxmint do the same?


You can use UUID's in Mint Elyssa ... there are some issues with UUIDs not being reported correctly for some USB/Firewire devices but you should be OK with internal devices.
To find out the UUIDs of the disks, boot from the Live CD, open a terminal and enter :

Code: Select all
sudo blkid


This will list the devices and their associated UUIDs.

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Re: Why no UUID's?

Postby plowna on Sat Sep 27, 2008 10:16 am

Sorry, I probably should have clarified that point. I understand that under linuxmint you can use UUID's to specify drives. I was just wondering why it doesn't do it by default. At least, it didn't on my laptop. Is it safe to assume it doesn't for anyone else by default? (and as I understand it, Ubuntu does use UUID's by default - please correct me if I'm wrong though, its been a while since I installed Ubuntu)
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Re: Why no UUID's?

Postby miket on Sun Sep 28, 2008 5:49 am

Hi!

plowna wrote:Sorry, I probably should have clarified that point. I understand that under linuxmint you can use UUID's to specify drives. I was just wondering why it doesn't do it by default. At least, it didn't on my laptop. Is it safe to assume it doesn't for anyone else by default? (and as I understand it, Ubuntu does use UUID's by default - please correct me if I'm wrong though, its been a while since I installed Ubuntu)


I think the default usage of UUIDs was dropped in Elyssa (Mint 5) as it was causing problems ... I know Elyssa has a lot of problems with USB/Firewire devices UUIDs not being
detected correctly ...

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Re: Why no UUID's?

Postby Lolo Uila on Mon Sep 29, 2008 4:17 pm

I honestly don't know why Ubuntu (or anyone) would bother with UUIDs. They have been a source of much trouble, and don't seem to have any advantage at all. I usually edit fstab and replace UUID with the /dev/ device identifiers and it has never been a problem (it has, in fact, solved and prevented problems for me).

The whole UUID thing seems pointless to me.
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Re: Why no UUID's?

Postby merlwiz79 on Mon Sep 29, 2008 4:42 pm

Ubuntu has their own grub and we use grub-gfxboot.
The grub-gfxboot will still boot if you use an UUID.
The grub-gfxboot doesn't use UUIDs by default, in fact it replaces UUIDs with the /dev/sdX.

The grub-gfxboot for Felicia has the last good boot, just like Ubuntu's grub.
It also has a fix for the missing message file problem when using a separate /boot partition.
I have backported it for Elyssa, but the grub-common from intrepid hasn't been for hardy yet.

The UUIDs do seem to mess up fsck.
The main reason they went to UUIDs is for the SATA drives.
The motherboard can't set a master for SATA drives, this way it will still boot when using the UUID.
But this doesn't always work on all hardware.
Also if the UUID of a hard drive is changed, the UUID doesn't get updated in grub, which makes the system not boot.
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