In the old days, doing a clean install was pretty much required for a major Mac OS X 10.x release. Is that still the case? Or should this graybeard let go of his old ways?

The MacBook in question works well. The hard disk gets high marks from Disk Utility app checks. Both a Time Machine and a full clone of the disk will be in place, each on their own external hard disk.

Going from Mountain Lion to Yosemite in this upgrade. Should I try simply running the Yosemite installer as being suggested by the App Store app?

  • You have your belt & braces in place, TM & clone, you checked perms & disk. Go for it. By the same method, my current machine is a direct line of descent from Tiger, via update & migrate.
    – Tetsujin
    Aug 17, 2015 at 5:47

2 Answers 2


To put it simply: yes, using the installer provided by the App Store is sufficient. Keep in mind that Apple develops and designs these installers specifically so that users, like you, can update to the newest system.

All you need to do is click the download button and follow the onscreen instructions to update.

There is always a risk factor of something going wrong; an obscure file missing, a .plist value out of whack, etc. The unfortunate truth is that there is always going to be potential human error.

Something to remember is that the error in question could come from something the new system added, rather than something the installer forgot to remove.

Using the installer is just a quick and easy way to update with a small chance of error. It adds new files and replaces outdated ones. If you wipe the system clean and freshly install a new one, there is still a small chance of error.

  • As I said, in the old days those in-place upgrades of Mac OS X almost never worked quite right. People with glitches, weird problems, and ghost-in-the-machine problems were almost always the people who did in-place upgrades rather than the clean-install people. I wonder if there is any evidence for that no longer being the case. Aug 16, 2015 at 22:53
  • I've added some more information. @BasilBourque
    – Zach Gates
    Aug 16, 2015 at 23:01
  • @BasilBourque Don't worry, it's completely fine to use the plain old installer from the App Store. Aug 16, 2015 at 23:02

“Lazy Man Works The Hardest”

Do the clean install.

I regret going the upgrade-upon-upgrade path. Many problems since. Just click my user account on this site to see my numerous questions about various problems. I suspect all of those are related to bugs and glitches and issues with doing layers of upgrades.

Just spent hours today with two Google accounts in Mail.app. Neither account showed any folders in the sidebar. Worse, the "Archive" area of the side bar showed all the same messages as the "Inbox". Long story short, I disabled the accounts, re-enabled them, created a new "ArchivedWithPurpose" folder, and used the Mailbox > Use this mailbox as > Archive Mailbox menu item to designate a clean empty folder as the archive location.

This is one of many problems that would not occur in a clean install.

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