Resolved [Solved] Booting to Recovery Mode from Time Machine backup drive

[Soba]

I posted this in the Mac Pro forum, but got no responses, so trying again here.

I am running High Sierra 10.13.6 on my 2010 Mac Pro. A while ago, I replaced the Time Machine drive mounted in SATA Bay 4 with a larger drive. I cloned the old drive to the new drive using SuperDuper! to preserve my backup history and then retired the old drive. Backups are running fine.

In past versions of macOS (starting with Mac OS X Lion 10.7.3), a recovery partition was created silently on Time Machine drives upon completion of the first successful backup. I used to see this in Startup Manager (holding Option at boot time) and it is documented by Apple on this page under "Learn More" :

https://support.apple.com/en-us/HT201250

I noticed recently that the recovery partition that allows booting directly from the Time Machine drive was missing. No boot option for the Time Machine drive shows in the Startup Manager and running `diskutil list` in Terminal shows only an EFI partition and the Time Machine data partition. (Edit: Time Machine drives are bootable for recovery purposes, but there is no separate recovery partition on Time Machine drives. See my post below for details.) I assumed this was because I used SuperDuper! to clone to the new drive, which would have cloned only the backup data partition, but in any case, it's possible my prior Time Machine disk did not have the recovery partition, either; I have replaced the Time Machine drive many times over the years and cannot recall when I last saw it appear in Startup Manager.

Assuming this is still supported, I would like the option of booting from the Time Machine drive in case of a disaster, so I removed the existing Time Machine backup drive from Time Machine preferences and unmounted the drive. I then erased another new drive connected via one of the USB2 ports, and as expected, macOS prompted me to use the new drive for Time Machine backups. I then let the first backup run to completion and macOS displayed the expected message saying the first backup was successful. I intended to then clone the entire drive using Carbon Copy Cloner to preserve the recovery partition.

But I never got as far as cloning because no recovery partition was created by Time Machine on the new drive. I tried the same procedure and re-wiped the new Time Machine drive on my Macbook Air 4,2 (also running 10.13.6) and got the same result. The Mac Pro and the Macbook Air have a few folders excluded from the backup, but these are folders such as my Downloads folder and large Fusion VM files, so I would not expect this to have any effect.

As I said, this used to work, so can anyone else confirm the behavior I'm seeing? Are recovery partitions no longer created on Time Machine drives in current versions of macOS? Or is this happening because of a quirk of my hardware, or even a bug in 10.13.6, perhaps?

Thanks for reading.

 

[CoastalOR]

To my Knowledge, SuperDuper! never dealt with Recovery partitions. Have you used SuperDuper! in the past to clone a Time Machine with a working Recovery Partition in the past?

I believe CCC does not support cloning Time Machine because of the hard links.

There was a bug with El Captian that Time Machine using El Captian did not have a working Recovery Partition. Other TM backups (other than El Capitan) include booting to the TM backup to Recovery.

 

[Soba]

Thanks for the response.

To my Knowledge, SuperDuper! never dealt with Recovery partitions. Have you used SuperDuper! in the past to clone a Time Machine with a working Recovery Partition in the past?

I have not, though this is moot for the moment because 1) This specific Time Machine drive probably never had the recovery partition to begin with, as I believe this is the 3rd Time Machine drive I have had in this system since I began my (current) backup history and the partition likely got left behind during a prior clone, 2) I cannot get a new Time Machine recovery partition in place to be cloned (hence my problem).

Having said that, SuperDuper! now supports recovery partitions (as of version 3.0). The feature was mentioned on his blog in 2017 and never appeared in the release notes, so I didn't even know about this until last week. I have never tested it, personally.

I believe CCC does not support cloning Time Machine because of the hard links.

I never looked into this, so thank you for pointing it out. I will double check.

There was a bug with El Captian that Time Machine using El Captian did have a working Recovery Partition. Other TM backups (other than El Capitan) include booting to the TM backup to Recovery.

I remember this bug.

The last time I remember seeing and using a Time Machine recovery partition was under Mavericks; it's not something I have used more than a couple of times over the years, so unfortunately I have no idea when I lost the partition.

My current thinking is—after I get a new graphic card—I will upgrade my Mac Pro to Mojave and see if I can get it to create a recovery partition on a fresh Time Machine drive. I already tried this on my Macbook Air under 10.13.6 and a clean install of 10.7.5, and it did not work on that system either, even though it's supposed to work from 10.7.3 onward. I've tried entirely different hard drives and two different drive enclosures, as well.

I'd like to try under Mountain Lion and later versions of macOS, but repeatedly reinstalling and backing up the MBA is a bit of a project and I haven't had time to dive into this, yet. (Expired certificates on the old installers and other such problems—even when re-downloaded from Apple—make installing the old OSes a bit of a dance.) I could also try Mojave on the MBA at some point, using dosdude's patcher, though I'm trying to keep the system as vanilla as possible so there are fewer variables to troubleshoot.

I'm quite curious exactly where the problem is.

 

[Soba]

@CoastalOR Thanks again for your post!

After a great deal of testing of every version of macOS going back to Lion on several Macs and VMWare Fusion VMs, I have a lot more insight into how this works.

I discovered that a lot of this was not documented (at least not in one place), so I am posting here to help anyone who might run into trouble in the future.

Time Machine backups are bootable on all versions of macOS / OS X going back to Lion 10.7.3, except for El Capitan 10.11, which has a bug that prevents booting from Time Machine drives. I verified this with my testing. If you try to boot from a Time Machine backup from El Capitan, you will probably see the Apple logo for a few moments, then you will see the prohibitory symbol and the system will refuse to boot. (I believe this might have worked in early versions of El Capitan, but I am not certain. Regardless, it does not work in 10.11.6.)

The Time Machine drive does not have a separate recovery partition. At the end of the first successful Time Machine backup of a Mac, Time Machine copies some important files from the existing system recovery partition and places them as hidden files on the Time Machine backup drive's main partition where backups are stored. These files are also recopied to the Time Machine drive during any later backups if they've been deleted or are missing. That is, they are safe to delete for troubleshooting because Time Machine will re-create them on the next backup.

Located in the root of the Time Machine drive is a hidden file called tmbootpicker.efi that is copied when the backup completes successfully. Within the Backups.backupdb folder, Time Machine also creates a hidden folder named .RecoverySets and several subfolders within. My testing showed that new subfolders are created (while keeping the older ones in place) if the system's recovery partition is changed so that the newer files required for booting are copied to the Time Machine drive. Located within these folders are many files, including BaseSystem.dmg, prelinkedkernel, and others needed for booting the Mac.

When these files are present, your Time Machine drive will appear in Startup Manager (the "boot picker") that you can access by holding the Option key when first starting your Mac. It might take the drive a few seconds to appear. If you do not see your Time Machine drive in Startup Manager after about 10–15 seconds, unplug and replug it. If you still do not see the drive, restart the Mac and clear the NVRAM by holding Cmd+Opt+P+R immediately after powering on the Mac. The Mac will restart, then you must release and immediately hold the keys again to reset the NVRAM a second time. Repeat this again to reset the NVRAM a third time, then on the 4th reboot, re-enter Startup Manager by holding the Option key. Your Time Machine drive should appear as a bootable disk.

If you still do not see your Time Machine drive in Startup Manager, there is something wrong with the recovery files on the drive. Boot back into macOS and open a Finder window on your Time Machine drive, then (on macOS Sierra or later), press Cmd+Shift+. (period) to show hidden files. (If this keyboard shortcut does not work on your version of macOS, your best option is to use Terminal to view and manipulate the hidden files from the command line.)

You will see the tmbootpicker.efi file in the top level of the drive and will also see a .RecoverySets folder within the Backups.backupdb folder. Delete this file and folder, empty your trash, then run a Time Machine backup. At the end of your backup, you should see these hidden files being re-created. Then, reboot your Mac and enter Startup Manager. Your Time Machine drive should appear as a bootable disk and you can enter recovery mode from there.

If you still do not see your Time Machine drive after the boot files are re-created, you might have a problem with your system recovery partition (which is what my problem seemed to be). Make sure you have a backup of your data, then delete all partitions from your Mac's SSD/internal hard disk (including the recovery partition; doing this requires that you work in Terminal and is beyond the scope of this post. Do not delete your Time Machine backups.) and reinstall macOS from scratch, which will create a fresh recovery partition. Then, when you are prompted later in the installation, transfer your information from your Time Machine backup (DO NOT SKIP THIS STEP). After your Mac is up and running again, delete the tmbootpicker.efi file and .RecoverySets folder from your Time Machine drive, empty your trash, and run a Time Machine backup so that the recovery files are re-created.

Your Time Machine drive should now appear in Startup Manager.

I also found during my research that some people had a problem where Time Machine creates these hidden .RecoverySets subfolders hundreds of times over because it mistakenly believed the system recovery partition had changed each time. This means that the recovery files grew to hundreds of gigabytes on the drive. If you have this problem and have deleted the .RecoverySets folder manually, but the problem continues to recur, your system recovery partition might be damaged. In this case, back up your Mac and then delete all partitions from the SSD/internal hard drive (including your system recovery partition) as described above. Again, be careful not to delete your Time Machine backups.

Good luck, everyone.