Why are my macOS system files huge? (Over 400gb)

My iMac has roughly 780gb in total and is running out of space (1TB partitioned for Windows using Bootcamp). I saw in 'About This Mac' that my system files are taking up 421gb while my actual documents and files are using only 388gb. I went into 'System Information' on my iMac to see if there was a way I could delete any of these, but 'System' is grayed out.

I used ncdu to try and find the files taking up so much space, but tells me that the hard drive has 388gb of files, and does not include the system files. How do I find the system file/files taking up all the disk space?

Also, I do not have time machine turned on. Using MacOS High Sierra on an iMac from mid 2010.

Solution 1:

I like to use CleanMyMac 3.app to take a look at my disk usage and help me clean up any disk space that could be reclaimed.

This includes unused language files in the system, huge system log files that need to be trimmed/rotate/deleted, user cache files, mail attachments, left over iPhoto junk, left over iTunes junk, empty trash bins, large and old files that may not be needed any more, etc....

It can also help remove things left behind when you just dragged a file to the trashcan and didn't remove all the other files that might be associated with it but are in other directories.

DaisyDisk is another good tool for helping you to visualize how much disk space is being taken up by what kinds of files.

Hope that helps!