System data keep increasing on Mac, even after deleting other files

deks123 wrote:

Why does the system data occupy so many space? The system data occupy 142.28G, even if i delete other big files, the system data will increase till my disk full, this is so weired, looks like it is a virus.

Official Apple Support Community

[Edited by Moderator]

OP wrote " looks like it is a virus. "

Part 1 of 2

Windows-like viruses that self-replicate and affect macOS don’t exist because of the underlying UNIX Foundation and permission limitations.

The macOS operating system resides in a sealed and read-only volume that can’t be opened by users or third-party applications.

Mac app security enhancements are sufficient to protect computers from malware.

Part 2 of 2

Reducing System/Volume/Data is a common question. 

1 -  System data taking too much in MacOS Sono… - Apple Community

2 - Time Machine Local Snapshot won't delete - Apple Community

3 - Over 60% storage blocked by System Data - Apple Community

How to free up ‘System Data’ and other storage on your Mac from a fellow colleague  @ neuroanatomist

Use another application to see where space is being used  Storeograph  on the Apple Apps Store 

View APFS snapshots in Disk Utility on Mac

Suggest getting an External SSD Drive and start moving your Pictures, Videos, Music and any other large files you have control over, OFF the Internal drive and Onto the External

Understanding iCloud Drive from a well written User Tip from @ Richard.Taylor

There are  two effective ways to remedy this issue:

1. Quick Fix Actions:

For Apple Silicon computers, use Disk Utility to erase a Mac.

For Apple Intel computers, use Disk Utility to erase an Intel-based Mac, then reinstall macOS.

Always make a Time Machine backup before proceeding.

Migrate only the user account, not the entire system.

   Reinstall only the necessary applications from the Apple App Store or directly from the developers.

2 - Generally

When the user discovers this issue, it’s likely because the computer’s internal drive capacity is small, such as 256 GB or 512 GB.

Unfortunately, the user’s storage needs may have increased since the computer was purchased. To future-proof the computer, consider spending extra money upfront on a larger drive capacity and adding more unified RAM.

Note - On Apple Silicon and newer computers. The SSD Drive and the Unified RAM are Soldered to the Logicboard and can not be upgraded.

You can prevent the recurrence of a large collection of Time Machine snapshots.

If you have Time Machine set to backup automatically at some interval but you don't keep the backup drive connected all the time, then TM will create multiple snapshots over the course of time until you reconnect the b/u drive.

If you disable automatic backup, TM will stop creating multiple snapshots. However, you will now have to run your TM backups manually from time to time as you see fit. Don't neglect that.

The other option is to keep your backup drive connected all the time while TM is configured to backup automatically.

Either option is a bit of a trade off for a laptop computer.

"System Data" comprises your data, but they are files that Spotlight cannot assign to a specific category like Documents or Applications. Examples include Outlook attachments, Cloud storage caches, and Time Machine snapshots. 

See this User Tip:

How to free up ‘System Data’ and other st… - Apple Community

Notice that in your screenshot it states at the top 'need permission to fully scan'. You should have been prompted to allow OmniDiskSweeper to access parts of your storage, e.g. the Library. Without that permission, it cannot index those areas and your Library folders are where most of the stuff that shows up as System Data is stored.

You don't have a virus.

System Data comprises log files, Time Machine local snapshots, and a bunch of other stuff. When you 'delete' files, they aren't really deleted they are flagged for later deletion by macOS and that doesn't happen until macOS decides it should.

Your initial screenshot does not show your full storage map, but if you've let your internal storage become nearly full that causes a whole host of issues and is difficult to recover from without drastic action.

不客气

Your are welcome

🦉-53

You do understand why this may have happened ?

When Time Machine Backup is on a Schedule and the Destination External Drive is NOT attached to the computer

TM Backup will keep the TM Snapshot (S ) on the Internal Drive Until the External Drive has been attached to the computer

TM Backup should transfer the Snapshot from the Internal Drive and onto the External TM Backup Drive

And, in so doing, Automatically remove / delate the 80 GB Snapshot from the Internal Drive

Just add additional information

Purgeable Space is controlled by the Operating System and not the user 

Get detailed information about a disk in Disk Utility on Mac