Disk by uuid

Question

In Grub, the root device is specified by UUID, example:
kernel /boot/vmlinuz26 root=/dev/disk/by-uuid/8def79a8-3257-4412-a9d3-fe95a55fcb06 ro
After I built my custom kernel, which doesn't need an initrd, booting using UUIDs no longer worked (I got a kernel panic saying that it could not mount the root fs). Using the traditional /dev/sdX way works fine however.
Please can someone verify that the usage of UUIDs is only necessary when using an initrd (because the initrd might change the /dev/sdX naming)? If it's not, then in what way do I need to change my kernel config so it can handle UUIDs?
Thanks!
Last edited by roog (2008-08-13 05:42:53)

Answer 1

roog wrote:Please can someone verify that the usage of UUIDs is only necessary when using an initrd (because the initrd might change the /dev/sdX naming)? If it's not, then in what way do I need to change my kernel config so it can handle UUIDs?
The need for uuids is because they are a naming system that almost guarantees that that uuid belongs to that partition: if you reformat that partition, then you can't boot the new partition using a uuid, since that isn't the same partition. /dev/sdx naming would try to boot the new one.
That is more an issue if you have multiple disks and switch them, or if you have two hdd controllers whose modules cannot be loaded in a predefined order (people see this more often with which network device is eth0, which is eth1), or if the driver changes between releases to call a disk /dev/sda instead of /dev/hda, or some other scheme.
In any case it is a more robust system to use uuids, but the other way works too!
The code that goes into the ata_piix might have some info, though something might pop up when you run diff (vimdiff?) on your config and arch's config.