On a MacBook Air running Sierra, I'm trying to create an image backup from my main SSD to an external USB disk using a clean shutdown, then during start: Command-R -> Disk Utility.

Both the main SSD and USB HDD get through "first aid" fine.

I'm not using file vault.

It fails right at the end (after the progress bar has been fully blue).

My Google tries all fail to return meaningful results:

The only result is from someone trying to create an ISO image from an optical disk: https://discussions.apple.com/thread/7663155?start=0&tstart=0

This is the screen during backup (sorry for a non-PNG one: when in Command-R mode, I could not find a way to make a proper screenshot).

On a Retina MacBook Pro with Yosemite this works perfectly fine.

Error 3, Status 5

3 Answers 3


I just experienced the same problem while trying to clean install Sierra. I had the same error until I asked Disk Utility to mount the internal SSD. When I did so, it asked for the password to unlock the drive. After unlocking the drive, I was able to create the disk image.

  • In my case, the SSD was not encrypted and the root cause is still unclear, but thanks for the tip as it will hopefully help other users. Commented Aug 22, 2017 at 9:11

After doing this in recovery mode then - without rebooting - open Terminal.app and check the logs to see if anything is written there to indicate the cause of the error.

In the Terminal run the command dmesg to see kernel messages. If you have disk I/O errors this is probably the cause of the problem.

If not you can try to do the image copy from the Terminal as this probably will give you better error messages when the error occurs. You can do the copy like this:

dd if=/dev/rdisk1 of=/dev/rdisk2 bs=1m

NOTE: It is very important to replace "rdisk1" and "rdisk2" with the correct disk numbers for your SSD and USB HDD. Replace 1 with the number of the source disk (SSD) and 2 with the number of the destination disk (USB HDD)

WARNING: Everything on the USB HDD will be deleted (including the partition table). The USB HDD will contain a bit-for-bit copy of the SSD. If you want to copy to an image file instead of a copying the image directly to disk, replace "of=/dev/rdisk2" with "of=/Volumes/USBHDD/myimage.img".

You can find the disk numbers in Disk Utility by opening the Info (Cmd-i).

The command will run without giving any progress information during the copy except for any errors it might encounter.

  • You should add that any content of the external disk will be erased and that the result is neither an image nor anything bootable or a legit disk/volume if you choose the logical volume (probably disk1 or disk2 with disk0=SSD)
    – klanomath
    Commented Jan 9, 2017 at 10:41
  • Thanks. I didn't realize there is terminal.app there too. I will try your suggestions after the transatlantic flight lands. Te USB HDD also has a time machine backup, so if all else fails I will dd to file. Final goal is to migrate this machine to a 13" retina MacBook, so I might get a Thunderbolt cable and use that for copying. I will report back the results for others to benefit. Commented Jan 9, 2017 at 10:42
  • @klanomath You're right - I'll add the warning that everything is erased. However the result is an image copy - i.e. the USB HDD will contain bit for bit what was on the SSD. I use this method all the time to copy the disk contents when I want to replace the disk on a computer, so the disk is bootable if you copy it over to another Mac or replace the disk and copy the contents back onto the original Mac.
    – jksoegaard
    Commented Jan 9, 2017 at 11:09
  • I've used Carbon Copy Cloner for the migration. It complained about one iTunesU episode that plays fine in iTunes before and after the migration. The really cool thing about CCC is that it creates a sparse image that the Finder can immediately mount instead of the hour long .dmg verification of a read-only .dmg that Disk Utility creates. Time permitting I will try dmesg later after we get back from holiday. Commented Jan 11, 2017 at 14:29
  • I have used dd to write Linux images to a USB, as a startup disk, but I have never used dd to back up a HD, though I am about to now. What does the “bs=m1” argument do? Commented Mar 2, 2019 at 20:19

Was having the same issue until I figured out that you have to unmount the "Macintosh HD" partition before creating the image. This creates an image which includes the Recovery HD partition. enter image description here

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