System Data on Mac: what it is and what to leave alone
System Data is the storage category for files that fit no other category: mostly files that macOS and your apps use while they run. macOS manages this category, and the Storage settings do not let you delete from it. This guide says what System Data contains, why it grows, what you can look at without risk, and what you should leave alone.
What is System Data on a Mac?
System Data is one of the categories in the storage bar, and Apple defines it by what is left over. You see it in Apple menu › System Settings › General › Storage. Apple describes it as the files that don't fall into the other categories. It includes:
- log files, caches and VM files;
- temporary files;
- fonts, app support files and plug-ins.
These files come from Apple and from the apps you installed. Earlier versions of macOS call the same category Other.
Why does System Data grow?
System Data grows and shrinks because macOS and your apps write these files while they work. Apple says the category varies in size depending on the current state of your Mac. A cache or a log file written today counts as System Data. So do the support files an app keeps outside your documents. The number you see on Monday can be different on Friday, and you did nothing wrong.
Can I delete System Data?
You can't delete System Data from the Storage settings. Apple says it plainly: you can't manage the contents of this category, because macOS manages them. Apple adds one exception. Your own data that falls outside the other categories can be managed with the Finder or with the app that created it. So the safe way to remove an app's data is to open that app and use its own settings.
What can I look at without risk?
Looking changes nothing, so you can look at every folder you can open. Start with the Library folder in your home folder, where your apps keep their support files:
- In the Finder, open the Go menu.
- Press and hold the Option key, then choose Library.
- Select a folder and choose File › Get Info, or press Command-I, to see its size.
A disk map does the same check for every folder at once. Choose your home folder in DiskSphere and it draws the folders inside your Library by size, so you see which app holds the space. DiskSphere is honest about its limit: macOS reserves some folders for the system, and no app can read them. When you scan the whole disk, DiskSphere counts those folders and reports the space it could not map as one figure, “System and other”.
What should I not touch?
Do not delete, move or rename anything you can't name the purpose of. Three rules keep your Mac working:
- Leave the System folder alone. It contains macOS.
- Leave the Library folder at the top level of your disk alone. It contains items used by apps for all users of your Mac.
- In the Library folder of your home folder, look, and delete nothing by hand. Use the app that owns the folder.
DiskSphere follows the same rules. It refuses to move system folders, your home folder and its Library.
What can I free instead?
Free the space in the categories you can manage; that is where Apple points you. Apple's own list includes: empty the Trash, delete files in your Downloads folder, delete old device backups, and delete apps you no longer use. Two guides help you find those files: How to find large files on a Mac and What's taking up space on your Mac?
Questions
What is System Data in Mac storage?
System Data is the storage category for files that don't fall into the other categories: log files, caches, VM files, temporary files, fonts, app support files and plug-ins.
Can I delete System Data on my Mac?
You can't delete System Data from the Storage settings. macOS manages the contents of this category.
Why does System Data change size?
macOS and your apps write caches, log files and temporary files while they work. Apple says the category varies in size depending on the current state of your Mac.
Is it safe to delete files in the Library folder?
Do not delete files in the Library folder by hand. To remove an app's data, open that app and use its own settings.
You know what System Data is, and you know it is the one category to look at and leave alone. Next, free space where you can: start with your large files.