Difficulty with macOS Upgrades

I’ve had occasion to upgrade two MBA (Retina, 13", 2018) this last week, and both have proved to be reluctant to allow upgrades. They were running Mojave, and in both cases a download of Monterey via Software update resulted in a failed install. One managed to download and install an update to Mojave, but still failed the Monterey install. Internet here is such that we are talking ~6 hours for the 12GB download too. I resorted to using the recovery disk to reinstall Mojave, and then the Monterey install worked. With the second one, Mojave is on the final version. It has so far failed 2 Monterey downloads - goes all the way through 12+GB then says the download failed. Thought I’d be clever and transfer the saved Monterey installer from the first MBA, but it wouldn’t run. Altered security prefs but it still wouldn’t run. Started up into recovery and altered the security settings there, but before trying it decided to get the latest compatible system with an Opt-Cmd-R startup, which offered me Big Sur (not sure why - the MBA supports Monterey) and then that failed after several hours! Now doing a reinstall of Mojave from the recovery partition, and then I will try the Monterey installer again.
It never used to be this hard! Do other people have these problems too?

PS After two hours stuck at “2 minutes remaining” I got cross and restarted it. Came up with Mojave, still at the final version. At least the installer for Monterey is running now. I’ll have to wait and find out if it works.

That failed too. Now downloading the InstallAssistant.pkg directly from Apple to try to make an installer on an external SSD.

Well that fails to bless the external disk. And the Monterey installer downloaded direct from Apple also fails with the same message “Installer is damaged. Re-download file.”

What to try next?

Yes, there have been scattered reports from some enterprise ITs about updates/upgrades from various older macOSs with differing error messages. Also one complaint of Kernel panics post-successful Mojave->Monterey 12.6 upgrade. Haven’t seen any foolproof solutions yet.

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Had a terrible time last year upgrading my 2017 iMac (Fusion drive) from Mojave to Big Sur - ended up having to reset (ie wipe) the drive and start again as for a new computer. Now I haven’t got the courage even to consider upgrading to Monterey :(

Today I turned off SIPS and all security measures. Upgrade still failed with the same message. Currently downloading Big Sur and going to try that as an intermediate step.

SIP could not be at fault for your problems as anything signed by Apple automatically overrides all SIP restrictions, What does occasionally work is to startup in Safe Mode and install from there.

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Big Sur installer also failed with an error, so now I have erased and reformatted the SSD from the recovery partition, and set it re-installing Mojave. I’ve kept the installers for Big Sur and Monterey on an external drive.
And that got stuck at 2 minutes remaining again, and this time no system was installed (question mark on folder at startup). Trying internet recovery again to see if an erased disk helps. The only other thing I can think of is to start up in target disk mode and copy a system to it with CCC.

If you’re now erasing the SSD, you may want to make bootable Monterey installer, boot that, and use it to erase/install everything. Why bother going through an upgrade process if you can just install the final version directly?

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Well, because I tried to make a bootable installer, and after several tries it failed to ‘bless’ successfully.

Is it always the «Installer is damaged message?»

That’s what I get whenevr I try to run an installer from the startup disk. Internet recovery gave me “An error occurred.” and the recovery reinstall option just hangs with two minutes to go. I have now managed to make a Big Sur bootable installer on another machine, so if the current internet install fails (4+ hours to go!), I will try that.

I can tell you, you are not the only one. A year ago, I was trying to upgrade from Mojave to Big Sur. I got exactly that «damaged» error every time when starting installer from /Applications. After trying a lot of download options, I got hold of one of the first versions of Big Sur 11.01 or something like that, and then it worked. My feeling is that somehow the installers I downloaded were not full installers, although that is what they were supposed to be.

The “installer is damaged” message is displayed whenever the cryptographic authentication fails. This can be because the installer has been corrupted. It can also be because it is old and the certificate (from Apple’s server) needed to validate it has expired.

This happens all the time for iOS updates - Apple stops signing old installers soon after newer ones are released, preventing users from installing any version other than the latest.

For macOS, they don’t usually do this, but their certificates do eventually expire. The last time this happened was in 2019 - macOS installers downloaded before that date no longer work and you’ll have to re-download it (if the version you want is still available) in order to get one with a non-expired certificate.

But I don’t think this is your problem, because you have re-downloaded the installer and it didn’t help.

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I’ve had to give up. The internal SSD has been wiped, save for the recovery partition, but reinstalls from that partition or from the internet fail. The bootable installer I made results in the spinning globe of the internet partition. It’s well and truly effed up. I suppose I could drive 100 miles to the nearest Apple store and hand it in, but is it worth it? I’ve recently undergone a bone marrow transplant for leukemia and I’m not supposed to go out and catch Covid, being immunosuppressed. I think it’s going to joint the stack of old Macs.

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You can try using the working mac to install on the other by using target mode. You can try first if you can boot the not working mac from the working mac in target mode. The working mac will then function as an external boot disk. I recommend renaming the working macs disk to something else than the other before you start. If this works format the not working disk to MacOS extended. This will make the installer start with building APFS first. There are bugs with MacOS installers and APFS that have been made with older MacOS. To set up target mode: Transfer files between two Mac computers using target disk mode – Apple Support (UK)

If this does not work, you can try the other way around. Setting the not working mac as target disk. Have a look at the last comment here about the quality of cable you need. https://www.reddit.com/r/apple/comments/9ce3k8/install_macos_from_another_mac/

I’m going to take a day off from it, having had two days of frustration. Then I’ll start up the recovery partition, make sure all security features are off, and try the target disk mode.

Since you were near giving up, now you can let it rest for some days. That might even be a smart thing to do if the problem is at Apple’s end.

Do not waste your time with disabling security when you are ready to try again. Like @alvarnell writes, the installer from Apple will not have any problems with security.

If you use the disk on your working mac in target mode (startup with T depressed) you can start the other mac with option/alt and select the working macs disk as startup disk. No need to start in recovery.

Possibly, stupidly, I decided to get on with it. First mistake was to try to use CCC, which no longer copies the System to make a bootable disk.
Currently about to try the Monterey installer on the target disk Mac.