System files too large

Boot into Recovery (⌘-R) and run Disk Utility : First Aid on the boot drive. Then reboot normally. This misleading visual storage gauge will appear differently, and will remain a misleading gauge of storage usage.

I have also found from personal experience that booting into Safe Boot mode, followed by a normal reboot can alter this gauge appearance, and may also reclaim storage from System caches.

My hard drive was nearly full and after checking "Storage" tab in "About This Mac" it showed that "System" was accounting for some 900 GB of my 1TB Hard Drive. Searches suggested mainly that it was probably caused by copies of backups made by Time Machine. I did everything I could find in Terminal etc but to no avail (there were no copies by the way, only those on my attached external hard drive)

Eventually I fired up a program I had called "Find Any File" - don't remember where I got it from but it was free. I asked it to find any file bigger than 50GB (I did try smaller amounts but it returned thousands so went for a big number to reduce the returns)

At the top of the returned list were 3 AOL files, totalling 550GB!! I deleted them (brave I know but heyho) and after emptying the rubbish bin and then a restart (important because no gain registered at that point) and all was resolved.

The AOL files incidentally were as a result of a large email sent that was too big for AOL to handle and somehow it kept a log of each attempt to send - in its entirety. Thats another story..

Well worth a try - I spent 9 hours messing about with this...

The Storage tab is known to report incorrectly.Also check by choosing your Mac HD and "Get Info" (command-i). It may be different. Try rebuilding Spotlight index.

How to rebuild the Spotlight index on your Mac - Apple Support

Some of the space may also be from Time Machine Snapshots.

About Time Machine local snapshots - Apple Support

After you've freed up some space download Omni DiskSweeper:

https://www.omnigroup.com/more

DiskSweeper can give you a more accurate read of disk space than Finder or Storage Tab of About this Mac. Itcan also show you the precise size and location of all your files. It will inventory your disk starting from the files that take up the most space. If you want you can even delete files from OmniDisk Sweeper. But be careful some of the items may be important to your system.

Check Mail menu > Window > Connection Doctor. If you have check marked “Log connection activity” turn it off.

For information about the Other category in the Storage display, please see Apple Support Topic

https://support.apple.com/en-us/HT202867

Also, empty the Trash if you haven't already done so. If you use iPhoto, empty its internal Trash first:

iPhoto ▹ Empty Trash

In Photos: File ▹ Show Recently Deleted ▹ Delete All

Excellent fix. 🙂

Find Any File...

http://apps.tempel.org/FindAnyFile/index.php

Hold Option or alt key when selecting Find to Find All.