This post is about the trouble I ran into looking for said UUIDs...
I have 6 hard drives in my server, 2 have 3 partitions each (boot, swap, root) and are raid mirrored, the other 4 have 1 each and are set up as raid 5. I'm only concerned with the first 2 for this post. After seeing the error about mounting the swap on the last bootup I figured it would be an easy fix. I knew how to list the UUIDs so I typed in that command and was greeted with a seriously lacking list of partitions:
# ls -l /dev/disk/by-uuid/As you can see, none of the partitions from hde are listed, and only the one from hdg is listed. I'm not sure how or why the other ones are not listed.
lrwxrwxrwx 1 root root 10 2008-01-25 19:44 c2ceffb9-90be-4564-a946-9d37de7725ba -> ../../hdg2
lrwxrwxrwx 1 root root 22 2008-01-25 19:44 ca583626-4a25-4af7-b6c5-8e59a502dbc2 -> ../../mapper/vg-ballzy
lrwxrwxrwx 1 root root 22 2008-01-25 19:44 f5cc881f-210a-431f-8d52-f1e5b512b57b -> ../../mapper/vg-backup
Since the swap partitions weren't mounted I first tried mkswap to just "reformat" the swap:
# mkswap /dev/hde2Ok, Looks good so far. Let's try turning it on:
Setting up swapspace version 1, size = 1028153 kB
no label, UUID=56c2f2af-86dd-4390-ae1a-c7fb71e6ed05
# swapon UUID=56c2f2af-86dd-4390-ae1a-c7fb71e6ed05But...mkswap just told me the UUID...how can it not be found?!?!?
swapon: cannot find the device for UUID=56c2f2af-86dd-4390-ae1a-c7fb71e6ed05
After a little digging, I came up with the vol_id command and it clued me in to the problem:
# vol_id /dev/hde2Raid member? OK, I admit, I used to mirror my 2 swap partitions, but after seeing the performance I decided against the protection it afforded and just went back to adding 2 separate swap partitions. It seems the raid superblock was still in the partition and mkswap wasn't overwriting it for whatever reason.
After another quick google search for deleting a raid superblock, I found the proper command and here are the results:
# mdadm --zero-superblock /dev/hde2Ahhh, the real UUID, and it sees it as swap as well. I then proceeded to update the /etc/fstab after which swapon -a correctly enabled both swaps. As to why the UUIDs are not listed under /dev, I don't know. Maybe after a reboot the other swap will show up? The other /dev/by-* listings show all the partitions properly.
# vol_id /dev/hde2
EDIT: Since I'm running Gentoo, a simple udevstart causes udev to restart. Now,
ls -l /dev/disk/by-uuid/shows both hde2 and hdg2 :).