"Disk almost full" message

try Restart

then Disk Utility>First Aid

Exactly the same here as well, though on a Mac Mini Late 2012. Have never seen it prior to upgrading to macOS Sierra. More than 300Gb free on a 500Gb HDD so there is no issue with space. Disk Utilities reports no errors (though I haven't tried running it from Restart Recovery mode).

I've just put it down to yet another spurious glitch

Type the command "df -h" (minus the "s) in a Terminal window and paste the output here.

I Have the same problem. It is not a memory problem from the file end As I too have significant space left. I was on the beta of Sierra. I may do a complete wipe and install clean OS.

Same here. Almost 500GB of free space, but since updating to macos Sierra this keeps popping up for me.

Same here on a Mac Mini with over 900GB free space on a 1TB fusion drive. It's only started happening since I upgraded to Sierra.

The cynic in me wants to say that this is just a ruse to make people purchase bigger iCloud plans...

I get this problem too, and it's very annoying.

I think you may be onto something there!
I was looking on the internet about this and it seems it's something to do with the 'new' way files are handled in Sierra to optimise space and with how a fusion drive works (this isn't a technical explanation, so apologies to anyone who knows all the technical ins and outs).
As I understand it, if you have a fusion drive your Mac puts files it 'thinks' you may want to access quickly onto the Flash drive, as they can be retrieved faster. These are the very files that Sierra recommends you to move onto iCloud when you are asked if you want to free up space on your hard drive. So it looks as though Sierra is just telling you that the flash part of the fusion drive is getting full (so it will move some of that onto the regular part of the drive).
Now, I don't know exactly how this ties in with standard HDs or whether the message is actually meant to appear on Macs with fusion drives but, as you say pauley123, it's very annoying when you know you have plenty of space!

BTW I do keep my photos on iCloud, paying the minimum subscription, but I keep them on my Mac too.

Hi

It is an interesting idea but I don't think it is the answer as my Mac Mini just has a standard SATA hard disk rather than a solid state one (which is what I think you mean by a Fusion drive ?).

Having said that I have only had the error twice since I upgraded to Sierra. I think Sierra does a lot of indexing of files (Photos, etc in the background) and I am wondering if this is some sort of what Windows would call File Allocation Table error, where basically the disk content is fine but the FAT/directory structure gets corrupt so it thinks the disk is fuller than it is. I haven't been able to tie the error instances into any specific tasks or apps running

A fusion drive is where a standard hard drive and a flash drive are configured as though they are a single drive. I was just repeating what I'd read about files on fusion drives but if it's happening on standard HDs then it probably is just a coincidence about the suggested files. No-one seems to really know why this message comes up though, as far as I've seen, just speculation as to why it's happening.
I've only had it a few times since upgrading to Sierra but it's annoying as I've so much free space on my HD.

Yes. Me too. 500GB hard drive in a mid-2010 MacBook Pro with over 300GB of available space, 4.29GB purgeable. Used space is 188GB. I only started getting drive almost full messages with the latest update.

I had this problem today.. only 250 mb available when it should have been 700GB. After a restart all was well. I rang my local Apple authorise repairer and the answer I got went something like this:

"Yes I had this problem recently" and (being a guru) he knew what to look for.... presumably invisible files. He said that when Sierra rebooted after the update it didn't clear out the Time Machine temporary file that was on the main hard drive.

That comment made my day.

I am wondering if this is a small bug that needs to be fixed.

Woke up to full disk. The utility tool claims I have more than 600GB of "Documents", something which is not true, only about 8-9GB. My disk is a 750GB all flash on a late 2012 MacBook Pro. I also backup to a Time Machine.

I believe this might have something to do with the iCloud Disk: I ticked the box for copying my "Documents" folder to iCloud. Several days have passed without the iCould Disk feature has completed the copy. I have not worried about it before I got the "disk full" alert.