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Old 03-20-2005, 03:04 AM   #1
ALT147
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Disk image problems

OK, I downloaded a disk image the other day and now I'm having a hell of a time trying to get it to open.

Double-clicking in the Finder brings up a window with the "no mountable filesystems" error.

Doing "diskutil mount pathtofile.dmg" from the Terminal gives "Volume xyz mounted" but I can't see it on the Desktop and it doesn't appear in the Volumes folder.

If I open Disk Utility and drag the dmg file to the sidebar, I have the option to "Open" it from the toolbar. I click on this, it gives me a progress window saying "Attach image" then "Initializing..." then "Attaching..." with a barber pole, then the options "Mount" and "Eject" appear in the toolbar. Clicking "Mount" does nothing. The Disk Utility log file reads:

Attach image "xyz.dmg"
Initializing...
Attaching...
Finishing...
Finishing...
Image "xyz.dmg" attached sucessfully

I can also use "hdiutil attach" from the Terminal, I have no idea what this does but I've heard it is possible to attach and then run fsck on it. I did this, and fsck says: BAD SUPER BLOCK: MAGIC NUMBER WRONG and asks if it should look for alternate superblocks. Typing 'n' quits the fsck and typing 'y' gives a "search for alternate super-block failed" and something about using the -b option.

So...what else can I try??? Before anyone suggests, my bandwidth and the size of this file prohibits the possibility of re-downloading it. And the fact that the Disk Utility log thinks that the mount was successful should mean that there isn't a problem with the dmg file itself, right?

Any ideas? I've tried everything I know.
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Old 03-20-2005, 05:06 AM   #2
bramley
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Quote:
Originally Posted by ALT147
Double-clicking in the Finder brings up a window with the "no mountable filesystems" error.

Quote:
Originally Posted by ALT147
I did this, and fsck says: BAD SUPER BLOCK: MAGIC NUMBER WRONG

These two statements are effectively saying the same thing. Your problem is probably because of a bad checksum on the disc image (i.e it's corrupt)

If the image is read only, you can run in a terminal window:

hdiutil verify pathtodmg

I suspect you'll get an error. i.e the checksum is bad - the image is corrupt.
You can try:

hdiutil attach -ignorebadchecksums pathtodmg

And see if it mounts. But don't hold your breath! I'd make plans to reacquire the disc image, I'm afraid.

Quote:
Originally Posted by ALT147
Any ideas? I've tried everything I know.

It is possible to instruct disc images to mount at other points on your system, not necessarily at /Volumes. I think you don't get an icon in Desktop. You can try:

hdiutil info

after the image has apparently mounted, and see where the image is actually mounted (but only if it truly mounts which I suspect it not the case)

Sorry - it's not good news

Last edited by bramley; 03-20-2005 at 05:08 AM.
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Old 03-20-2005, 05:44 PM   #3
ALT147
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Thanks for the reply.

OK, doing "hdiutil verify" says that the file has no checksum. What does that mean?

"hdiutil attach -ignorebadchecksums" gives the "attach failed - no mountable file systems" error again.

And "hdiutil info" just gives framework, revision and vendor information (76.4, 10.3.4d76.4, Apple).

I'm still confused as to why diskutil and the Disk Utility log report a successful attach? Are you sure there's no way to get it to work?
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Old 03-21-2005, 03:15 AM   #4
voldenuit
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Check if there is a checksum posted with the image and make sure your copy gives the same when checked.

If it's an MD5 checksum, type

md5sum nameofimage.dmg

Results should be identical, otherwise your image is corrupt.
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Old 03-21-2005, 03:58 AM   #5
bramley
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Quote:
Originally Posted by ALT147
OK, doing "hdiutil verify" says that the file has no checksum. What does that mean?

If the dmg is not read-only there will be no checksum. Type: "hdiutil imageinfo pathtodmg" and check the "Format description:" property. You should also see that the various checksum properties are missing. Note the lack of a checksum doesn't mean that the disc image isn't still corrupt - it just means you can't check to see if it is.
Quote:
Originally Posted by ALT147
"hdiutil attach -ignorebadchecksums" gives the "attach failed - no mountable file systems" error again.

No surprise here. No checksum so this is effectively the same as "hdiutil attach"
Quote:
Originally Posted by ALT147
And "hdiutil info" just gives framework, revision and vendor information (76.4, 10.3.4d76.4, Apple).

Again no surprise. The image is not attached.
Quote:
Originally Posted by ALT147
I'm still confused as to why diskutil and the Disk Utility log report a successful attach?

Neither of these apps attaches disc images. They pass on the request to the Disc Image framework, so as far as they are concerned all is well. So log details concerning disc images from these apps are meaningless.
Quote:
Originally Posted by 147
Are you sure there's no way to get it to work?

A serious pay-as-you-go expert with a good knowledge of the data on the disc image, and access to your disc image might be able to resolve the issue. In your case it'll be less time and money to get a new copy of the disc image.
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Old 03-21-2005, 06:53 PM   #6
ALT147
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OK, thanks for the help guys. I guess I shouldn't have got my hopes up

By the way, md5sum gives a "command not found" on my machine...
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Old 03-21-2005, 07:04 PM   #7
voldenuit
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Sorry, md5sum is not part of OS X, fink installed it.
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Old 03-21-2005, 07:32 PM   #8
trevor
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Quote:
Originally Posted by voldenuit
If it's an MD5 checksum, type

md5sum nameofimage.dmg

Quote:
Originally Posted by ALT147
By the way, md5sum gives a "command not found" on my machine...

Quote:
Originally Posted by voldenuit
Sorry, md5sum is not part of OS X, fink installed it.

True, but md5 is part of OS X. Using the syntax given, md5sum nameofimage.dmg you will get exactly the same checksum result using the md5 command included with OS X:

md5 nameofimage.dmg

For example, these are md5 checksums of the same .dmg file (with only the name of the disk image genericized):

% md5 nameofimage.dmg
MD5 (nameofimage.dmg) = 443bcd8fec98210c2f60ca90c40bd027

% md5sum nameofimage.dmg
443bcd8fec98210c2f60ca90c40bd027 nameofimage.dmg

Trevor
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Old 06-05-2008, 09:00 PM   #9
kps000
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I'm having the exact problem with a backup image i created! There's no way of reacquiring the data I have formatted the disk, and was attempting to restore my data when I ran into this

Is there any way out ??
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