Upgrade OS on M1 , 2021 iMac to Tahoe from Sequoia

straightshooter wrote:

Thank you den.thed and Owl-53 for your recommendations. I did start working through the options offered but found I was being stymied part-way through each. After sleeping on the problem I decided on the nuclear action and delete the drive, upgrade to Tahoe and restore from Time Machine. However, I discovered that the Time Machine drive had apparently died last November (still attached, light would blink but not showing on desktop) so no back-ups since then.

You should always verify the backups and even manually initiate a backup right before erasing a device. In fact double check the backup is accessible as well.

I theorised that Apple (in their wisdom) prevents system upgrades if an installed Time Machine drive hasn't been backed up to for some time in case it accidentally deleted wanted files during the process.

I don't think this had anything to do with it. I've never heard macOS ever preventing an OS upgrade for issues with a backup. The more likely scenario is whatever caused your backups to fail is also probably responsible for the inability to see any upgrade options.

A very likely possibility is an issue with third party software which is interfering with the normal operation of macOS. Usual culprits are anti-virus software, cleaning & optimizer apps, and third party security software.....none of which are needed on a Mac.

Sometimes you may need to install an update patch for the current OS before it may allow you to download & upgrade to a new major version.

Many times a simple reboot can fix things, other times booting into Safe Mode may help. Other times it may help to toggle the software update settings. And once in a while it may be necessary to reset the software update settings (I don't recall specifically how to do this one).

Just to add to the good advise already provided

Use the Terminal application found in Finder >> Go >>> Utilities

Copy and paste the below command and depress the Return key

softwareupdate -l 

This command will only check for possible upgrades that computer qualifies to install

Does it report seeing Tahoe 26.5 ( current version ) ?

If yes there are several option available

In no specific order

1 - Restart in Recovery Mode and choose Reinstall macOS. 

This in theory will pull the latest version of macOS this computer qualifies to run ie Tahoe 26.5

2 - Again in Terminal and the below command (copy and paste, return key )

softwareupdate --fetch-full-installer --full-installer-version 26.5 

This will manually download load the Full Version of Tahoe 26.5

It will make a new application in the Application folder called " Install Tahoe app "

When ready, launch it like any other application and follow the prompts

The installer will self delete once a successfully installation is done

Start out with > Update macOS on Mac - Apple Support

If that doesn’t help, see > If an error occurred while updating or installing macOS - Apple Support

Thank you for the detailed work you have shared 👍

Though, like @HWTech

Have not seen where a Failed TM Backup drive would have interfered with the upgrade process

Not to pour water on what has been achieved and yes we are pleased the machine is once again functional with Tahoe

Though, something does not add up, on face value/

Unless there was a second functional TM Backup used and in service

"I decided on the nuclear action and delete the drive, upgrade to Tahoe and restore from Time Machine."

Then later:

"However, I discovered that the Time Machine drive had apparently died last November ... so no back-ups since then.

I am sorry but this seems quite the reversal from the previously stated position " After sleeping on the problem I decided on the nuclear action and delete the drive, upgrade to Tahoe and restore from Time Machine "

In this context and in the order of appearance in this question

It is implied IMHO " nuclear action and delete the drive " was the Internal Drive " of one of 2 x 24-inch, M1, 2021 iMacs

People to change their minds before " Pulling the Trigger "

That we accept as being human

straightshooter wrote:

After the reply from den.thed my investigation led me to use Terminal to download the Tahoe installer but the Installer failed to complete downloading the OS. I repeated this, but for Sequoia, with the idea of updating to the latest version but encountered a similar problem.

I have encountered the OS installer failing to complete the download a number of times on various Macs where they had no software issues. It has even happened to my own laptop from time to time. I finally created a script to use which would restart any incomplete download using the "softwareupdate" command line utility since it would take multiple restarts of the command to even get it to 80% or so, but if I didn't keep an eye on the progress & it failed....if I waited too long to restart the command .....it would start over at 0% (or maybe something else was a play). At least when I arrived at work the next day the installer was fully downloaded which was all that mattered.

After installing a new Time Machine drive and letting it complete its first backup, ...

It was after 11pm, after I was reasonably happy that most major issues had been resolved, I decided to check if Tahoe was available on the iMac in question before I went to bed, and lo and behold, it was! I started the installer downloading Tahoe and went to bed. This morning I entered the required password to install Tahoe which it completed without any problem. Had this not occurred my next step would have been to nuke the Hard Drive.

I appreciate that you guys may have never encountered the OS updater being stopped by a failed Time Machine issue but I believe that I did nothing to this iMac during all this process that would have had an effect on the OS. Restoring Time Machine was the ONLY thing I successfully managed to do.

I have seen cases in my organization where some macOS updates will not be shown. Sometimes they will just magically appear a few days later. Sometimes I have been able to get macOS to force a new search for macOS updates. I know there are a couple of methods to clear out the software update list/cache to trigger a fresh search for updates, but I don't recall those steps at the moment. I know that they don't always work either. It does not help that Apple doesn't provide any documentation in this regard. Apple products have many strange & mysterious quirks. This is one of them.

Thanks for the expanded update. Of course we are glad you were able to find a way through the obstacles to achieve your goal which is the most important thing.

Thanks for the update. Glad to hear that you were able to upgrade to Tahoe.