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I am having problems booting a new Ubuntu 10 (server) install. My primary HD (/dev/sda) is laid out as follows:

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          18      144553+  83  Linux                  <-- /BOOT
/dev/sda2              19      182401  1464991447+   5  Extended
/dev/sda5              19        2207    17583111   fd  Linux raid autodetect
/dev/sda6            2208       11934    78132096   fd  Linux raid autodetect  <-- / (ROOTFS)
/dev/sda7           11935      182401  1369276146   fd  Linux raid autodetect

The rootfs is part of a RAID1 (software) array (currently degraded):

# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md2 : active raid1 sda6[1]
      78132032 blocks [2/1] [_U]

The UUIDs for the partitions are as follows:

# blkid /dev/sda1
/dev/sda1: UUID="b25dd301-41b9-4f4d-9b0a-0e31713dd74c" TYPE="ext2"
# blkid /dev/sda6
/dev/sda6: UUID="af7b9ede-fa53-c0c1-74be-31ec752c5cd5" TYPE="linux_raid_member"
# blkid /dev/md2
/dev/md2: UUID="a0602d42-6855-482f-870c-6f6ecdcdae3f" TYPE="ext4"

Finally, I have my grub2 menuentry setup as follows:

### BEGIN /etc/grub.d/10_linux ###
menuentry 'Ubuntu, with Linux 2.6.32-25-server' --class ubuntu --class gnu-linux --class gnu --class os {
        insmod ext2
        insmod raid
        insmod mdraid
        set root='(hd0,1)'
        search --no-floppy --fs-uuid --set b25dd301-41b9-4f4d-9b0a-0e31713dd74c
        linux   /vmlinuz-2.6.32-25-server root=UUID=a0602d42-6855-482f-870c-6f6ecdcdae3f ro   nosplash noplymouth
        initrd  /initrd.img-2.6.32-25-server

When I attempt to boot, grub loads OK, however I eventually get the following error message:

Gave up waiting for root device. ALERT /dev/disk/by-uuid/a0602d42-6855-482f-870c-6f6ecdcdae3f does not exist. Dropping to a shell!

If from the grub bootloader I open a grub> command line, I can ls (hd0,) and it lists the correct partitions with the UUIDs as shown above - sda6 shows 'a0602d42-6855-482f-870c-6f6ecdcdae3f' (the RAID UUID). If I ls (md2)/ it properly lists all the files on the RAID1 filesystem (ext4) so it doesn't appear to be an issue accessing the raid device.

Does anyone have any suggestions as to what the problem might be? I can't figure this one out.

share|improve this question
When it drops you to a shell, is /dev/md2 active and running without you having to force it to start? You mentioned it's degraded, and I've had trouble getting a degraded array to autostart in the past. – Darth Android Oct 5 '10 at 22:15

I eventually found the answer via Google.

I had to add the kernel parameter rootdelay=90 to the linux /vmlinuz... line in grub.cfg.
The system then boots without issue. It doesn't even take very long (perhaps 30 seconds from POST to Ubuntu login prompt). It seems to be a little known / little documented workaround for this issue.

share|improve this answer
Could you mark your answer as the solution to your question? – Oliver Salzburg Feb 29 '12 at 22:16

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