My goal is to create a clean install of MacOS, yet still have access to the old install (somewhere else like another partition) while I work on the new install to match the old one. I am assuming that I will miss some items initially and will need to refer back to the older install.

One path to accomplish my goal would be to have a dual boot (though not preferred). While I am working on the clean install, I would be able to reboot to the older version to perform work if necessary UNTIL the new clean install is ready. Eventually I would delete the older version.

Another path could be to create a virtual box install of High Sierra, time machine back up that, while I work on making that right I would still have access to the old install (host). Then once I'm convinced that I have everything ready I would backup and restore the new virtual install as a real install on my Macbook.

Does anyone have any advice to accomplish this?

  • 1
    A "clean install" by it generally accepted definition means to wipe the disk and install the OS so that the only thing on the disk is the freshly installed OS and nothing else. Therefore, you cannot keep anything that previously existed on the disk and call it a "clean install". – user3439894 Oct 18 '17 at 15:15
  • RIGHT, so I perform a clean install THEN install what I need after. All this while I still have access to the old install so I can reference things like the apps I had installed. This is the point. No one leaves an install clean. I don't see the point of your comment. – ktamlyn Oct 19 '17 at 0:43

My goal is to create a clean install of MacOS, yet still have access to the old install while I work on the new install. I am assuming that I will miss some items initially and will need to refer back to the older install.

This is the very essence of a (full) Time Machine backup and the proper application of Migration Assistant.

Another option is to use an external USB drive and make an image of your existing drive to that external drive. Once you are certain that you can boot from it and operate properly, you can then do a clean installation on your internal drive.

To make a clone of your drive, you can use a commercial application like Carbon Copy Cloner or use dd in Terminal to make the copy:

dd if=/dev/diskX of=/dev/diskY bs=1M

Where X is your source (internal) disk identifier and Y is your target (USB) disk identifier.

Whether you use a commercial piece of software or the terminal command you need to make sure your target disk is the same size or larger than the source.

  • My original comment was about dd but you actually can restore a .dmg image of a larger disk to a small disk providing the contents of the .dmg made on the larger disk is smaller than the destination disk even when the size of the destination disk is smaller then the disk the .dmg image was made on. So that said, the update you made after my first comment is not totally true, depending on which method is used. In other words, I can restore a .dmg image made of original 756 GB SSD from my MBP to 40 GB disk, without issue because the original install is only ~10 GB. – user3439894 Oct 18 '17 at 16:57
  • True, but I am trying to keep this at the novice level. Technically, I could have piped it to a .gz (compressed file) to make it even smaller, but I don't want to create complexity where I don't need to. – Allan Oct 18 '17 at 17:10
  • Sounds like you are recommending that I move my install to an external drive, then install fresh on my internal drive. Your wording implies that I can use migration assistant alone, which I doubt based on the page you linked to. – ktamlyn Oct 24 '17 at 10:02
  • Migration Assistant and moving your install to another separate drive are two distinct options. If you had a current and complete TM backup, you would be able to use MA to move all your relevant data over. I've done it many times. – Allan Oct 24 '17 at 11:28
  • My concern includes things like losing Filezilla presets during the migration. Of course I an in this case export them, but invariably I forget one or another thing to migrate. – ktamlyn Oct 25 '17 at 12:43

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .