How to determine UUID for disk image?

In article
<Patrick.Stadelmann-2C2E70.09490204032004 DeleteThis @news.fu-berlin.de>,
Patrick Stadelmann <Patrick.Stadelmann DeleteThis @unine.ch> wrote:

> In article <me-72E9F2.19591703032004 DeleteThis @news.fu-berlin.de>,
> "Fletcher T. Penney" <me DeleteThis @privacy.net> wrote:
>
> > How can I determine the UUID for these disk images after converting
> > them? I can do it using Cocoa, or I can do it using shell commands -
> > either will work for this application.
>
> If you want to do this without mounting the image, I don't know... If
> the image is mounted, the command :
>
> /System/Library/Filesystems/hfs.fs/hfs.util -k diskXsY
>

Huh - I thought tried that yesterday with no success, but today it
worked.

BUT, the UUID I get is a 16 character one. When I encrypt a diskimage,
the password in Keychain Access references an account with a 32
character UUID ( in the format I am more accustomed to seeing UUID's
in...) I had assumed that this was the UUID for the disk image, but
perhaps this is a poor assumption?

I have found references at macosxhints to mounting disk images by UUID
in the fstab file. Is it possible to mount a disk image by UUID from
the command line or programmatically, NOT at boot time?



I am trying to track disk images that are created by my application, and
thought that the UUID would be a better means of doing this ( in case
files are moved, renamed, etc...) But this might not be the case...


Any thoughts?


F-

In article <me-616F25.16370504032004.RemoveThis@news.fu-berlin.de>,
"Fletcher T. Penney" <me.RemoveThis@privacy.net> wrote:

> I am trying to track disk images that are created by my application, and
> thought that the UUID would be a better means of doing this ( in case
> files are moved, renamed, etc...) But this might not be the case...

You want Aliases, not UUIDs, as far as I know. UUIDs have nothing to do with
tracking disk files across moves/renames.

meeroh

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In article <macdev-8E0E50.00494805032004.DeleteThis@senator-bedfellow.mit.edu>,
Miro Jurisic <macdev.DeleteThis@meeroh.org> wrote:

> You want Aliases, not UUIDs, as far as I know. UUIDs have nothing to do with
> tracking disk files across moves/renames.
>
> meeroh

No - I DO want UUID's, if they work. I understand aliases, but am
looking for a better way of doing this.

My understanding is that all disk images contain a UUID, unless you
specify --nouuid when creating it. When you double-click an encrypted
disk image in the finder, it asks for you password. If that password is
in your keychain, it seems to be "linked" to the disk image via a
UUID-like account reference. I had THOUGHT that this was the UUID for
the disk image (like a serial number) and there are references on the
internet to being able to mount a disk image by UUID rather than file
name/path in fstab ( check macosxhints for this).

I would LIKE to be able to mount a disk image by UUID, but am not sure
if this is possible. If not, then of course aliases/filename is the
only way to go, but UUID would be nice....


Fletcher

In article <me-3B8A8F.15540605032004 RemoveThis @news.fu-berlin.de>,
"Fletcher T. Penney" <me RemoveThis @privacy.net> wrote:

> In article <macdev-8E0E50.00494805032004 RemoveThis @senator-bedfellow.mit.edu>,
> Miro Jurisic <macdev RemoveThis @meeroh.org> wrote:
>
> > You want Aliases, not UUIDs, as far as I know. UUIDs have nothing to do
> > with
> > tracking disk files across moves/renames.
>
> No - I DO want UUID's, if they work. I understand aliases, but am
> looking for a better way of doing this.

They don't.

> My understanding is that all disk images contain a UUID, unless you
> specify --nouuid when creating it. When you double-click an encrypted
> disk image in the finder, it asks for you password. If that password is
> in your keychain, it seems to be "linked" to the disk image via a
> UUID-like account reference. I had THOUGHT that this was the UUID for
> the disk image (like a serial number) and there are references on the
> internet to being able to mount a disk image by UUID rather than file
> name/path in fstab ( check macosxhints for this).

Your interpretation is correct in that:

1. There is a UUID in every disk image except those created by older OSes or
those created with --nouuid.
2. You can put attach a UUID to every HFS+ partition

However, there is no way to map a UUID to an arbitrary volume. The only way that
the system knows which UUID corresponds to which disk is by finding the disk
during the boot time device search, and then remembering the UUIDs of all disks
it sees.

On other words, the first time the OS will learn the UUID of a disk image is
when you mount the disk image. This is clearly not useful to you.

> I would LIKE to be able to mount a disk image by UUID, but am not sure
> if this is possible.

No, it is not. The problem is very simple: UUIDs identify volumes, but you are
not trying to identify a volume, you are trying to identify a file (which
happens to be a disk image, but that is completely irrelevant).

hth

meeroh

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