Hi Mario,

With a manual or tutorial to hold my hand I can navigate grub just fine, but luckily it didn't come to that.

I tried mounting the USB stick to look for that file as you requested, but it didn't automount (strange), and when trying to mount manually:

sudo mount /dev/sdb1 /mnt -t vfat

it refused to mount, showing this in the log file:

FAT-fs (sdb1): invalid media value (0x63)
FAT-fs (sdb1): Can't find a valid FAT filesystem

To indirectly validate the presence of .disk/casper-uuid, I mounted the .iso image from Downloads/ as a loop device, and indeed, it's there.

I then tried to build boot media again, this time on a USB hard disk. This built fine and the file was there and everything, but for some reason the laptop refused to boot from this disk.

I started seriously suspecting the USB stick but as seen before, when an image is burned it works fine. So I suspected filesystem size. The only peculiarity about this USB stick is that it's 16GB, which sounds big for a VFAT filesystem. I manually built a 5-GB filesystem on the stick (using fdisk and mkfs.vfat) and just specified "make startup disk" while creating the boot media (not erasing it as before).

First off, this does automount when I plug it in, and I see .disk/casper-uuid there. Also, happily, the USB stick now boots the recovery utility without problems.

I guess the same problem that kept Ubuntu from recognizing the hard disk also caused grub to be unable to read the filesystem, and thus fail to find .disk/casper-uuid.

Looks like I'll have to get a 4- or 8-GB stick to keep my recovery backup.

I'd be OK with marking this bug as Invalid as it was due to the too-large USB stick, but I'll let you decide on the status, in case you want more information on what makes this stick fail so strangely.

This USB stick is a 16-GB ADATA USB 3.0 unit, here's the lsusb data:

Bus 002 Device 010: ID 125f:312b A-DATA Technology Co., Ltd. Superior S102 Pro
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.10
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x125f A-DATA Technology Co., Ltd.
  idProduct          0x312b Superior S102 Pro
  bcdDevice            a.00
  iManufacturer           1 ADATA
  iProduct                2 ADATA USB Flash Drive
  iSerial                 3 0000000000000400
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           32
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass         8 Mass Storage
      bInterfaceSubClass      6 SCSI
      bInterfaceProtocol     80 Bulk-Only
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
Device Status:     0x0000
  (Bus Powered)