A Big Problem with Migration Assistant
I bought my first Mac in 1992 and have been upgrading them ever since, and as a rule with little trouble. A vital part of that process since 2005 is what’s done by Apple’s “Migration Assistant” program. The process can be carried out as the longest and most consequential step of the initial setup or it can be put off until later.
Migration Assistant is found in the Utilities folder. To run it, the two Macs need to be able to communicate with one another, generally over your local network, and in many cases the best option for speed is for both to be connected via Ethernet. The process will typically take a few hours to run.
Migration Assistant will copy some files from the old Mac to the new one, and ignore others. It generally does a good job of discriminating between those it should copy over and those it should not. Many things can cause it to not work. Apple has a generally good description of the process here:
https://support.apple.com/en-us/10261
which is, however, lacking one crucial piece of advice, without which one might never succeed in migrating one’s data to the new Mac. At least that was my experience migrating the data in a 2012 iMac running High Sierra to a 2024 iMac running Tahoe, over the last few days. I found many shortcomings with the process, but one of them was a doozy, and it’s not covered in any of the several references I could find about problems one might have getting Migration Assistant to run to completion.
I tried eight or nine times before the process finally ran successfully. It should have taken one. Here’s the problem. With this move, i.e. from this older Mac and OS to this newer Mac and OS, it is vital that the new Admin user account on the new Mac not have the same name as any of those of the older Mac! The option which the UI provides to "Replace _____" (the existing account of the identical name) did not work! The process would always hang before files actually started to be transferred. Perhaps this is a new bug? If so, then it's the sole reason for this article. Also, the phrase "Keep a copy of the data..." is dangerously flawed because it doesn't state which data are being referred to.
For example, if the old user name was “jholmes” with full name “Joseph Holmes”, the new user name must unfortunately be different in some degree for the process to run, in my repeated experience of the last few days. Apple’s documentation and UI content are inconsistent regarding which of the two names is the user name, but I suspect it’s the more abbreviated one, and it may be the case that only that name needs to be different, or both might need to be different. I suspect that your password need not be different.
Also, you must be logged in using the different user name in the new Mac. If you already created the identical user name for your new Mac, as I assume most of us would prefer to do most of the time, then it will be important to delete the identically named new user account entirely. You can’t delete a user account while you are logged into it. Sign out of it and sign into a new account with a different name, then delete the identically-named account. Then proceed to run the process.
When you run Migration Assistant, it must be run on both machines. On each machine you must select which direction the data are going, e.g. from computer A to computer B or vice-versa.
It was my experience this time that the successful run (and only that run) was marked by a series of indications of thousands of files having been processed. However, after about 5 minutes, some 95,000 files had been processed but the indications of progress then ceased entirely for at least 80 minutes. Despite this rather horrid and quite odd cessation, the process did complete overnight.
Obviously if this issue can stop the process cold, Apple badly needs to warn us to avoid duplicating the user account name! There were so many things that went wrong you could be forgiven for thinking they weren’t any longer very interested in the entire Macintosh line. But the one big one was this simple issue of avoiding a duplicate user name.
One other thing that Apple's documentation needs to do a much better job of explaining is what happens to your access to your files when they're deemed to belong to a different user? This looms as a huge problem over the entire process yet is overlooked entirely in the documentation.
Another detail to keep in mind: If you have a Dropbox account, and thus a Dropbox folder on your old Mac, the entire Dropbox folder (directory) and its contents will not be moved to the new Mac, presumably because Apple can anticipate that the Dropbox folder that will be added to the new Mac when the Dropbox app is added to it and run for the first time, will automatically be populated with the files in question via the hub and spoke system that Dropbox uses to simplify sharing files between your computers. Dropbox can also help to share files with other people and there is a file backup feature as well.
That’s it! Good luck with your next upgrade. Try to remember this tip! And Apple, do try to ensure that we can use our same user name for the new Admin account for any new Mac, without any trouble.
PS: Here are two other articles about troubles with Migration Assistant:
https://setapp.com/how-to/migration-assistant-not-working