Re: "error: invalid magic number" when booting from ISO loopback

[Vladimir 'phcoder' Serbinenko]

Ron wrote:
> On Sat, 2009-10-31 at 18:30 +0100, Robert Millan wrote:
>   
>> On Sat, Oct 31, 2009 at 06:01:56PM +0100, Ron wrote:
>>     
>>> Hi,
>>>
>>> I was playing around with Grub2 (latest svn version) and its loopback
>>> feature and had some problems to boot an ISO. The ISO file is the 32Bit
>>> version of Ubuntu 9.10 which is located on a 8GB USB flash drive with
>>> one FAT32 partition. I've tried to boot it with the following menu
>>> entry:
>>>
>>> menuentry "Ubuntu" {
>>>     set isofile="/boot/isos/ubuntu-9.10-desktop-i386.iso"
>>>
>>>     loopback loop $isofile 
>>>     linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile
>>> quiet splash noprompt --
>>>     initrd (loop)/casper/initrd.lz
>>> }
>>>
>>> This entry fails silently and when the commands were executed one by one
>>> the linux command shows the error message "error: invalid magic number".
>>>       
>> This error means vmlinuz wasn't read correctly.
>>
>> This could be either a problem in loopback/iso9660 or a problem in the
>> partition that contains ubuntu-9.10-desktop-i386.iso.
>>
>> Can you figure out which applies?  For example, if you put a physical CD
>> with ubuntu-9.10-desktop-i386.iso in the drive and access it from
>> GRUB (via ata.mod), are you able to load Linux this way?
>>
>>     
>
> I'm sorry but right now I can't burn a CD. But I made some more test
> with the ISO file that doesn't work and the copy from it that does work.
> As I've mentioned both files shows the same correct MD5 sum under Linux.
> Also GRUB shows with the ls command the same file size of 723488768
> Bytes (690 MiB) for both of them. But the output of the blocklist
> command is looking wrong.
>
> blocklist output for the ISO that doesn't work:
> 11833144+161304, 13766112+8, 13853680+218800, 14072488+118288
>
> blocklist output for the ISO that does work:
> 15128592+328728, 11652008+16, 11654088+1792, 11655888+8,11655912+440,
> 12089440+16, 12404120+126080, 12530256+99464, 12629728+761984, 13413432
> +94536
>
> So if you sum up the sectors from the ISO that doesn't work and multiply
> it with 512 you get only 255180800 Bytes (243 MiB). It looks like the
> blocklist command encounters an error and exits before it is done, but
> no error message is visible.
>
>   
Can you disable offset checking in kern/disk.c and retry?
> Some more info that may help.
>
> blocklist output from the vmlinuz file from the mounted ISO file (both
> ISO files show the same output):
> 1384372+7598, 1391970[0-224]
>
> fdisk -lu output from the USB flash drive:
> Disk /dev/sdb: 8086 MB, 8086618112 bytes
> 255 heads, 63 sectors/track, 983 cylinders, total 15794176 sectors
> Units = sectors of 1 * 512 = 512 bytes
> Disk identifier: 0x2c6b7369
>
>    Device Boot      Start         End      Blocks   Id  System
> /dev/sdb1   *          63    15791894     7895916    b  W95 FAT32
>
>   
>
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>
>   


-- 
Regards
Vladimir 'phcoder' Serbinenko
Personal git repository: http://repo.or.cz/w/grub2/phcoder.git