How I Re-Imaged My Mac Computers in My Lab

I wanted to start the school year with a new clean slate by re-imaging my computers in the lab. This process involved the cloning of a computer hard drive that I customized and reinstalling it to the rest of the computers. The hard drive I cloned, or imaged, included the specific applications I wanted my students to use, specific OS settings, and numerous Chrome extensions that block inappropriate ads on the browser. Imaging your computer is also a great way to back-up your important data.

All this could not have been done with the help of Jacob in the IT department.

Steps to Image Your Computer:

1. Open your Disk Utility application and click on the “New Image” icon.


2. Name your dmg file and save it to your desktop.


3. Plug in your external hard drive and upload the dmg into it.

Steps to Re-Image Your Computers:

1. Restart your computer.


2. Hold down the Option key during the restart of your computer.


3. Click on Recovery HD


4. Plug in your external hard drive to your computer that contains the dmg file.


5. Choose your language.


6. Click on Disk Utility.


7. Choose your hard drive on the left-hand side.


8. Click on “Restore.”


9. Click on the “Image” button and choose your dmg file.


10. Double-click on your dmg and click “Skip”.


11. Double-click on the bottom “Macintosh HD”.


12. Drag the first “Macintosh HD” into the “Destination” box.


13. Click on the “Restore” and “Erase” button.



4 thoughts on “How I Re-Imaged My Mac Computers in My Lab

  1. Thanks, very useful!

    Please note that you cannot make an image of the current disk. That would be like sawing the branch you sit on. 😉

    You would either have to:

    1. partition your main disk with 2 Mac OS X, then start the computer using the “other” partition, run Disk Utility from the “other” partition to copy the “golden” partition to the external HDD

    2. restart the computer, press Option, go to Recovery, then run Disk Utility from the Recovery

    El Capitan (10.11) has a new Disk Utility interface, but the functionalities are still there, in the menues.

  2. I cloned an image from unit 1 (specs seen below) via Time-Machine and re-imaged unit 2 (specs seen below) using the clone from unit 1. The system on unit 2 runs, but seems to be a bit sluggish. My actions were actually a practice run to re-image 30 Late model 2015 iMacs (specs seen below). Can anyone help me/direct me on how to do this in a proper manner? It seems that for the image to work correctly, it must come from an identical unit meaning a unit that has the same specs. Also, is Time Machine okay to use (it’s pretty simple)?

    I have seen tutorials that use Disk Utility or other software.

    Unit 1 Specs
    iMac (21.5-inch, 2018), Display – Retina 4K display, Processor – 3.6GHz quad-core Intel Core i7, Memory – 32GB, Storage – 1TB SSD, Graphics – Radeon Pro 560 with 4GB of VRAM​

    Unit 2 Specs

    iMac (21.5-inch, 2017), Display 21.5-inch, Processor 2.3GHz dual core Intel Core i5
    Memory 2.3GHz 8GB of 2133MHz DDR4 memory, Storage 1TB (5400-rpm) hard drive, Graphics Intel Iris Plus Graphics 640

    Unit 3 Specs
    iMac (21.5-inch, Late 2015), Display 21.5-inch (diagonal) LED-backlit display with IPS technology,
    Processor 1.6GHz dual core Intel Core i5, Memory 8GB of 1867MHz LPDDR3, Storage 1.6GHz 1TB (5400-rpm) hard drive, Graphics 1.6GHz Intel HD Graphics 6000

    Thank you in advance for your time concerning this matter.

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