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Over the past few days, I have downloaded both the 32 and 64 bit version of server and desktop to install on an Intel based PC.

It is normal from within OS X to double click on an ISO and it will mount the ISO in the finder as well as within disk utility.

When I attempt to mount any of the Ubuntu ISOs I downloaded, OS X returns the error message The following disk images couldn't be opened. The reason given for the error is no mountable filesystem.

However, I am still able to open the ISO directly from disk utility and burn it to a DVD/CD.

What has changed in this release to cause this? Is there something wrong with the current ISOs?

The OS X machine I am using is only two weeks old and is having no issues with any other ISO.

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@EliahKagan The OP appears to be referring to an error message displayed when you attempt to mount any of the 12.04 install ISOs in OS X. I tried mounting validated downloads of ubuntu-12.04-desktop-amd64.iso and ubuntu-12.04-desktop-i386.iso in OS X 10.6.8 (Snow Leopard) and verified you do get the error message the OP describes. I also mounted those images with no problems using the Daemon Tools and IsoBuster utilities in Windows 7. It appears to be a problem with how OS X mounts an ISO. But I don't know what it is about the composition of the ISOs which results in this glitch. –  irrational John Jun 20 '12 at 22:23
    
@irrationalJohn Can you confirm it doesn't happen with an .iso for an earlier version of Ubuntu? If so, then Fufus Rufus's answer about why this is happening is probably correct. –  Eliah Kagan Jun 20 '12 at 22:26
    
@EliahKagan I tried what I happened to have available without downloading. Both ubuntu-8.04.4-desktop-amd64.iso and ubuntu-10.04.4-desktop-amd64.iso mounted as expected. ubuntu-11.10-desktop-i386.iso did not. I got the same error message as for the 12.04 ISOs. –  irrational John Jun 20 '12 at 23:12
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To the hair-trigger "off-topic" closer: this is an extremely valid and on-topic question. Not every potential Ubuntu user uses Windows. –  izx Jun 20 '12 at 23:31
    
@irrationalJohn - thanks for your experiments confirming the problem, see detailed answer for reason with workaround. –  izx Jun 21 '12 at 1:51
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6 Answers

This is due to a bug (of sorts) in the package used to create the Ubuntu ISOs

  • Since 11.10, Ubuntu ISOs have been "hybrid", meaning that the ISO can also be written bit-for-bit to a USB device to make it a working Live-USB, without having to use StartUp Disk Creator, UNetBootin, etc.

    • Note that this "hybrid" is different from the OS X/Disk Utility definition of "hybrid", which simply refers to an ISO readable on both Mac (HFS+) and Windows (ISO9660).
  • Ubuntu's hybrid functionality is provided by the isohybrid script in the SysLinux bootloader. It works by encapsulating the standard ISO9660 CD filesystem within a partition, so that it will work unmodified if written to a USB/hard disk.

  • This patch/bug report discusses a problem in the way isohybrid sets GPT UUIDs, causing Disk Utility/OS X to fail to recognize the hybrid filesystem and consequently, failing to mount it. Hopefully it will be fixed at some point, making future Ubuntu hybrid ISOs compatible with Disk Utility.

Alternative to extract/explore Ubuntu ISOs on OS X: Keka

  • Keka is an open-source OS X frontend to the p7zip package, which is able to view and extract ISOs in addition to a myriad of other archive management features. While it won't let you "mount" the Ubuntu ISO on its own, it should let you view the ISO filesystem and extract what you need.
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Maybe because they are now hybrid (DVD/USB) ISOs which can be directly dd'ed to a USB drive and booted.1

1. https://lists.ubuntu.com/archives/ubuntu-devel/2011-June/033495.html

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@Eliah Kagan I interpreted his post that he could burn and mount but just not as doubleclick action. –  Fufus Rufus Jun 20 '12 at 22:04
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In case anyone else comes here because they were trying to install ubuntu in Vmware Fusion, but couldn't mount the iso, at least in Vmware Fusion 4, you can "Continue without disc" -- then it'll let you choose an iso on the next screen, so OSX never needs to mount it, and Vmware will mount it just fine.

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The only program extracting works with is the unarchiver for free from the app store. you can repackage it afterwards, but the plan would be to first be able to load any data at all.

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Clarify your answer. Explain more fully what you mean by "first be able to load any data at all". –  karel Apr 20 '13 at 14:08
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I faced the same error, after reading izx's answer, I used "The Unarchiver" app to extract the iso. It is also nice to know that one can now dd to have a working bootable usb.

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Convert the ISO in to a DMG.

hdiutil convert -format UDRW -o ~/Desktop/ubuntu-12.10-desktop-i386.iso.img ~/Desktop/ubuntu.iso)
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The conversion will appear to work, but you won't be able to open the resulting .DMG file. –  Lorin Hochstein Mar 8 '13 at 16:24
    
hmmm.. worked for me. –  jwerre Mar 8 '13 at 18:08
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didn't work for me –  Kem Mason Apr 19 '13 at 0:47
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