Disk image will not mount: "broken pipe" errors and more

[Published Thursday, July 5th]

In some cases, a disk image will not mount in Mac OS X, giving the error message "Unable to mount disk. Broken pipe," or another. There are various potential solutions for this problem:

Use Disk Utility's "Restore" function Follow these steps to use Disk Utility's Restore function to extract the contents of a disk image:

1. Launch Disk Utility (located in /Applications/Utilities and select a mounted volume (such as your startup drive)
2. Click the Restore button
3. Drag the problematic disk image from the Finder into the Source field, or click the Image... button and locate it.
4. Drag the drive on which you would like to place the files from the left-hand bar to the Destination field. (Make sure that the Erase destination box is not checked).
5. Click the Restore button
6. The files contained on the disk image should appear at the root level of the selected destination drive.

Re-download Simply delete the afflicted disk image, re-download from the original source and re-attempt mounting.

Boot in Safe mode If you are having a problem where disk images won't mount, try booting in Safe Mode (by holding down the Shift key while starting up), then re-attempting mounting of the disk image.

Delete kernel extension caches Delete the following files:

• /System/Library/Extensions.kextcache
• /System/Library/com.apple.kernelcaches

then restart, and re-attempt mounting.

Use an alternate tool Mount.app, FlashMount, or Toast Titanium can all sometimes succeed in mounting disk images where Mac OS X and Disk Utility fail.

You may also want to try using Pacifist to view and extract the contents of a disk image.

Re-apply combo updater Try re-applying the most recent Mac OS X combo updater from Apple's download page and re-attempting mounting.

Duplicate and force Apple has posted a Knowledge Base article (#305111) detailing an issue where users may receive the error message "Disk image you are opening may be damaged..." when attempting to mount disk images under Mac OS X 10.4.9. According to Apple, Mac OS X 10.4.9 is more robust in its ability to detect damaged or corrupted disk images. However, you may encounter this error when working with ostensibly functional disk images. The Knowledge base articles offers a process for dealing with the disk images identified as damaged, which involves first duplicating the disk image then forcing a mount by clicking the "Open" button when the error message appears; see the Knowledge Base article for further details.

Feedback? Late-breakers@macfixit.com.

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