How to Clear System Data on Mac

Thank you for posting this. I had over 800 gb of system data and I had no idea what to do besides erase and install again. I bought Daisy Disk and it solved that. It was all or mostly Time Machine related. I was down to 70 gb of free space and now it's 836.

🆓 Manually delete Time Machine backups using terminal commands

One of the most straightforward ways to clear system storage on your Mac is to delete invalid Time Machine backups. Time Machine also saves a local backup file in case external backups become inaccessible.

Normally, macOS should delete Time Machine backups when your Mac is low on storage, but that doesn't always happen. And, you probably don't want to wait until your Mac runs out of space to delete them. So, here's how to reduce system storage space on your Mac by deleting Time Machine backups. Keep in mind that this will delete the local copy of the backup, so don't do this if you feel at risk of a rollover.

1. Go to Applications > Utilities and launch Terminal.

2. When the Terminal window opens, type: tmutil listlocalsnapshotdates.

Press the "Return" key.

You will now see a list of your stored Time Machine backups, arranged by date.

3. Type: tmutil deletelocalsnapshots xxxxxxx, where 'xxxxxx' is the name of one of the backups listed. This will take the form of a date followed by a text string.

Press the "Return" key.

4. Repeat steps 1 and 2 for all backups you want to delete, checking the Storage tab in About This Mac each time to see how much space you've cleared.

Optimize your storage space

MacOS is equipped with some native tools to help manage files and storage in case of a possible lack of storage space. Specifically, you can go through the following steps:

1. Click the  Apple icon in the upper left corner and select "About This Mac".

2. Select the Storage tab and press Manage. In the window that appears, you can see some useful suggestions.

3. Store in iCloud" lets you move all your data to cloud storage and reclaim some space on your Mac.

4. You can also choose to delete some space-consuming files, such as movies and programs.

5. Turn on "Auto Empty Trash", this feature is very useful, it can help to remove unnecessary files in time.

Press "Review Files" and you will jump to the "Files" section. Look at the files stored on your Mac and pay attention to the "Unsupported Applications" category. It may contain programs that no longer work on your version of macOS.

delete duplicate files

For a mac, duplicate files can take up a very significant amount of storage space. Clean up duplicate files and help us get more free space.

Th paid version of DaisyDisk allows for forced reduction of "purgeable" space. Doing that always reduced my system space by a large amount.

The "Still Hidden" is not something DD can fix.

This might help: https://support.apple.com/en-us/HT206996