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User profile for user: NeonApples
NeonApples Author
User level: Level 1
4 points

Time Machine Recovery

I was upgrading my iMac's hard drive to a SSD drive this weekend. I did a Time Machine backup of the computer that started as a Mojave OS but is now Big Sur. Time Machine said everything was good and so I swapped the harddrive.


When I attempted to recover from Time Machine everything looked good when I logged into the backup and attempted to recover. It then reported that there was NULL data to recover and the process stopped.


I needed to get the computer back online so I started the recovery of the OS(Mojave) and after a day of loading and updating back to Big Sur, I tried to reload the Time Machine backup.


So far, so good, it looks like Time Machine will not recover a newer instance of the OS when in recovery mode. If that is the case, I would like to know how I can upgrade/update the recovery boot OS to keep it current as the computer ages? I would much rather have a 1 1/2 recovery time, not a day and a half.

iMac Line (2012 and Later)

Posted on Sep 20, 2021 3:37 PM

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User profile for user: Loner T
Loner T
User level: Level 9
59,526 points

Posted on Sep 22, 2021 3:43 AM

Using a NAS for TM requires the NAS to meet specific requirements. See Backup disks you can use with Time Machine - Apple Support for reference.


Think of a backupdb as a catalog, which has individual sparse bundle images. Here is an example. This is a Mac mini used as a Time Machine server.




Normally, there are two Recovery modes - Local and Internet.

  • Local Recovery (Command+R) should use the Recovery OS which is the same as the version installed on your internal disk. This requires the internal partition (Recovery HD) or volume (APFS Recovery volume) to be intact. If it is not available, then Local Recovery falls back to Internet Recovery.
  • For Internet Recovery, from How to reinstall macOS - Apple Support,
    • On an Intel-based Mac:
      • If you use Shift-Option-Command-R during startup, you're offered the macOS that came with your Mac, or the closest version still available.
      • If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac. Otherwise you're offered the macOS that came with your Mac, or the closest version still available.

Hopefully, this clarifies the behavior you have seen.

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User profile for user: Loner T
Loner T
User level: Level 9
59,526 points

Sep 22, 2021 3:43 AM in response to NeonApples

Using a NAS for TM requires the NAS to meet specific requirements. See Backup disks you can use with Time Machine - Apple Support for reference.


Think of a backupdb as a catalog, which has individual sparse bundle images. Here is an example. This is a Mac mini used as a Time Machine server.




Normally, there are two Recovery modes - Local and Internet.

  • Local Recovery (Command+R) should use the Recovery OS which is the same as the version installed on your internal disk. This requires the internal partition (Recovery HD) or volume (APFS Recovery volume) to be intact. If it is not available, then Local Recovery falls back to Internet Recovery.
  • For Internet Recovery, from How to reinstall macOS - Apple Support,
    • On an Intel-based Mac:
      • If you use Shift-Option-Command-R during startup, you're offered the macOS that came with your Mac, or the closest version still available.
      • If you use Option-Command-R during startup, in most cases you're offered the latest macOS that is compatible with your Mac. Otherwise you're offered the macOS that came with your Mac, or the closest version still available.

Hopefully, this clarifies the behavior you have seen.

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User profile for user: NeonApples
NeonApples Author
User level: Level 1
4 points

Sep 21, 2021 10:53 AM in response to jdo_apple

Appreciate the response. The response does not address the specific question of how to use Time Machine to recover from a backup when the Recovery Boot image is in an older OS version and the TM backup is in the most recent OS. When that occurs, the TM procedures in this link does not work. You can CMD R all day long, but it boots to the old OS, not the current version. When you do, you end up with a NULL back to restore from TM.

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User profile for user: Loner T
Loner T
User level: Level 9
59,526 points

Sep 21, 2021 11:05 AM in response to NeonApples

Connect your current TM disk to the iMac. Assuming there is a version of macOS installed on your iMac, what is the output of


diskutil list


from macOS Terminal show?


Normally, if your TM backup is using HFS+, it should be recognizable in all recent versions of macOS. However, if your backup is using APFS, then Mojave may have challenges. However, if you install Mojave (from Recovery Boot) and upgrade to the latest Big Sur, does it recognize your TM backup? Was the TM backup created on Big Sur or Mojave?

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User profile for user: NeonApples
NeonApples Author
User level: Level 1
4 points

Sep 21, 2021 3:39 PM in response to Loner T

Command Output from Diskutil:


Reports APFS Container Scheme on the Physical Store Disk0s2 1-6 which is the Mcintosh HD - Data, Preboot, Reocovery, VM, McInstosh HD and snapshot. Disk2 0-2 does not report either APFS nor HFS+. Disk3 reports APFS.


However, if you install Mojave (from Recovery Boot) and upgrade to the latest Big Sur, does it recognize your TM backup?

Yes. This is how I finally got the restore to work to restore the files/etc.


Was the TM backup created on Big Sur or Mojave? Big Sur.

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User profile for user: NeonApples
NeonApples Author
User level: Level 1
4 points

Sep 21, 2021 6:00 PM in response to Loner T

Short answer is yes, it is working as I expect.


Long answer is I really have never used TM so I don't know exactly how it should work. I used to do admin work on Windows environments, and cloning so in general I had a pretty good idea what to expect. I was upgrading to SSD for speed so I thought I'd give the TM a try. I also used my NAS device to backup and it worked very well. I didn't verify the only backup I did but figured, heck if I lose the image, I'll just reload because my files are on a server.


During recovery after the drive was replaced, it took me a few tries(read the prompts) to get the NAS share to mount(?) for the recovery, but after I got over that, it showed the image and things were looking good. Then when I tried to load it came up with a NULL error that I did not write down the exact message. I tried some quick searching and I did come across something about if the images extension was a *.sparsebundle or *.backupdb(???) My backup was a *.sparsebundle and I just figured the Mojave needed it to be a .backupdb. Since it was late, I just did the reload the OS and moved on.


Hopefully this is making sense and if I'm in the right neighborhood, I think the issue still comes down to the the Recovery OS that gets loaded/mounted for TM to work in recovery mode inherits back to the original OS installed from the factory which was Mojave. However since the upgrade to Big Sur, TM backups changed and can't be read by the older recovery TM.


If this is the case, then the question is can I upgrade the recovery OS environment to try to keep it in sync as the OS upgrades over time?


Appreciate the exchange and helping others learn a few things along the way, myself included.

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Time Machine Recovery

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