Time Machine could not create a local snapshot to back up from.

I solved it.  As I write the TM is doing its thing.

Let me tell you how.

I noted that there are a few local snapshots on the machine.   After all the machine was reporting: Time Machine could not create a local snapshot to back up from.

So, I checked how many there are with Terminal.

tmutil listlocalsnapshots /

This showed about 8 of snapshots and I figured maybe any of them or one is corrupted or the likes.  

So, I looked for a way to delete them via Terminal.

This is what I found:

sudo tmutil thinLocalSnapshots / 10000000000 4

A brief explanation of what it means: 

/ Refers to the primary hard drive, usually one does not need to change that.  10000000000 refers to how big the amount is one will want to purge.  In this example it is 10 GB. 

To purge more, increase the number to any value in bytes, or execute the command several times.  I ran it once and checked if any of them where left using the first command, and all were gone.

The 4 stands for “urgency”. 1 is the highest one can use, but 4 is seems enough to delete.

Presently the TM is doing a backup and slowly seems to write stuff to the disk. 

Hope this helps somebody out there with the same challenge.  

steve626 wrote:

First thing to check is free space on your boot up drive, as that is where the snapshots used for Time Machine are created. If there is plenty of free space, then other problems can also cause this, but the most common thing is lack of free space.

My OS disk is only two-third full. so that can not be it.

If you have an additional external drive available, try connecting it DIRECTLY to your Mac and see if Time Machine can complete to that drive. (Time Machine can be used with more than one backup drive, it will alternate between them).

I try that.

ach_du_lieber wrote:

Part of the problem might be the OS upgrade being forced to start *before* the Time Machine backup is complete (which is what just happened to me).

Thanks. Not here as far as i am aware.

I Tend to turn of any BU software before I upgrade. however I have not done any software updates for days and the TM worked fine til this AM.

steve626 wrote:

Usually the next step, if that does not work, is to start checking the file system of the disk (your internal drive), or next, to look into whether the disk is damaged or even failing. Because being unable to write snapshots is anomalous, that should happen with no impediments.

I did a hardware test and all is well. The SSD is also fine in a read and write test.

For the backup destination "MM (2020 model) in the network" -- what is that? Is it a supported configuration for Time Machine?

MM=Macmini

And yes this is a recognised way of doing it. And I have been for almost 15 years with no problems what so ever using Macminis.

steve626 wrote:

All is not well because your computer is unable too make snapshots or complete a Time Machine backup.

I am not sure if you are working in the right direction or not. will have an other look at it.