I've had this issue on and off for about two years now. I noticed it on a new (custom built) machine running 10.04 when that first came out, but then it went away until a few months ago. I've gone through a number of hard drive changes but I can't say specifically what if anything I changed hardware-wise to make it stop or start happening. I had assumed upgrading to a modern Ubuntu version would fix the issue, so I installed 12.04 beta on a spare partition last night, but it's still happening.

Here's the issue. After grub loads and I select a kernel to boot, the screen goes blank save for a blinking cursor. It sits in this state for many long minutes before it finally gives up and gives me an initramfs shell with the message gave up waiting for root device (and lists the /dev/disk/by-uuid/... path it was waiting for) but no other specific diagnostic information.

Now, here's the tricky part. For one, the problem is intermittent - sometimes it progresses from the blinking cursor to the Ubuntu splash boot screen in a few seconds, and once it gets that far it always continues booting fine. The really bizarre thing is that I can "force" it to "find" the root device by repeatedly pressing the space bar and hitting the machine's power button. If I tap those enough, eventually I will notice the hard drive light coming on, at which point it will always continue the boot process after a few seconds. Interestingly, if I wait slightly too long before pressing the power button (30s?), as soon as I press it I get the gave up waiting message and the initramfs shell.

I've tried setting up /etc/fstab (and the grub menu.lst or whatever it's called nowadays) to use device names (e.g. /dev/sda1) instead of UUIDs, but I get the same effect just with the device name, not UUID, in the error message.

I should also mention that when I boot to Windows 7, there is no issue. It boots slowly all the time just by virtue of being Windows, but it never hangs indefinitely. This would seem to indicate it's a problem in Ubuntu, not the hardware.

It's pretty annoying to have to babysit the computer every time it boots. Any ideas? I'm at a loss. Not even sure how to diagnose the issue. Thanks!

EDIT:

Here's some dmesg output from 10.04. The 15 second gap is where it was doing nothing. I pressed the power button and space bar a few times, and the stuff at 16 seconds happened. Not sure what any of it means.

[    1.320250] scsi18 : ahci
[    1.320294] scsi19 : ahci
[    1.320320] ata19: SATA max UDMA/133 abar m8192@0xfd4fe000 port 0xfd4fe100 ir
q 18
[    1.320323] ata20: SATA max UDMA/133 abar m8192@0xfd4fe000 port 0xfd4fe180 ir
q 18
[    1.403886] usb 2-4: new high speed USB device using ehci_hcd and address 4
[    1.562558] usb 2-4: configuration #1 chosen from 1 choice
[   16.477824] ata16: SATA link down (SStatus 0 SControl 300)
[   16.477843] ata19: SATA link down (SStatus 0 SControl 300)
[   16.477857] ata3: SATA link down (SStatus 0 SControl 300)
[   16.477895] ata15: SATA link down (SStatus 0 SControl 300)
[   16.477906] ata20: SATA link down (SStatus 0 SControl 300)
[   16.477977] ata17: SATA link down (SStatus 0 SControl 300)
[   16.478003] ata12: SATA link down (SStatus 0 SControl 300)
[   16.478046] ata13: SATA link down (SStatus 0 SControl 300)
[   16.478063] ata14: SATA link down (SStatus 0 SControl 300)
[   16.478108] ata11: SATA link down (SStatus 0 SControl 300)
[   16.478123] ata18: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[   16.478127] ata6: SATA link down (SStatus 0 SControl 300)
[   16.478157] ata5: SATA link down (SStatus 0 SControl 300)
[   16.478193] ata18.00: ATAPI: MARVELL VIRTUALL, 1.09, max UDMA/66

After that, it took its sweet time, and I had to keep hitting space bar to coax it along. Here's some more dmesg output from a little later in the boot process:

[   17.982291] input: BTC USB Multimedia Keyboard as /devices/pci0000:00/0000:00
:13.0/usb5/5-2/5-2:1.0/input/input4
[   17.982335] generic-usb 0003:046E:5506.0002: input,hidraw1: USB HID v1.10 Key
board [BTC USB Multimedia Keyboard] on usb-0000:00:13.0-2/input0
[   18.005211] input: BTC USB Multimedia Keyboard as /devices/pci0000:00/0000:00
:13.0/usb5/5-2/5-2:1.1/input/input5
[   18.005274] generic-usb 0003:046E:5506.0003: input,hiddev96,hidraw2: USB HID 
v1.10 Device [BTC USB Multimedia Keyboard] on usb-0000:00:13.0-2/input1
[   22.484906] EXT4-fs (sda6): INFO: recovery required on readonly filesystem
[   22.484910] EXT4-fs (sda6): write access will be enabled during recovery
[   22.548542] EXT4-fs (sda6): recovery complete
[   22.549074] EXT4-fs (sda6): mounted filesystem with ordered data mode
[   32.516772] Adding 20482832k swap on /dev/sda5.  Priority:-1 extents:1 across:20482832k 
[   32.742540] udev: starting version 151
[   33.002004] Bluetooth: Atheros AR30xx firmware driver ver 1.0
[   33.008135] parport_pc 00:09: reported by Plug and Play ACPI
[   33.008186] parport0: PC-style at 0x378, irq 7 [PCSPP,TRISTATE]
[   33.012076] lp: driver loaded but no devices found
[   33.037271] ppdev: user-space parallel port driver
[   33.090256] lp0: using parport0 (interrupt-driven).

Any clues in there?