How to Clear System Data on Mac and Reclaim Storage

Before You Start

System Data is macOS's catch-all category for caches, logs, temporary files, virtual memory swap, Time Machine local snapshots, and app support data. Not all of it is junk, so the goal here is to remove only the parts that are genuinely disposable. If you want the full explanation of what lives in there, read what System Data on Mac actually is first; if the issue is a free-space mismatch, see why purgeable space may not look free yet.

Step 1: Clear App Caches

Caches are almost always the largest recoverable slice of System Data. They live in ~/Library/Caches, and apps rebuild them automatically, so clearing them is the highest-value, lowest-risk move.

1. Open Finder and, from the menu bar, choose Go > Go to Folder (or press Command + Shift + G).
2. Type ~/Library/Caches and press Return. You'll see a sub-folder for nearly every app you've installed.
3. Sort by size. Switch to list view and click the Size column so the biggest folders rise to the top.
4. Quit the app first, then delete its cache. For each large folder belonging to an app you recognise, quit that app, then move the folder to the Trash.
5. Leave folders you don't recognise. When in doubt, skip it — you're only after the obvious large offenders like browsers, Spotify, Slack, and dev tools.

Step 2: Delete Old Logs and Diagnostics

Logs and crash reports accumulate forever and are only useful when you're actively debugging a problem. They live in ~/Library/Logs (your user logs) and are safe to clear.

Use Go to Folder again and enter ~/Library/Logs. Select the contents you no longer need — old app logs, diagnostic reports — and move them to the Trash. Avoid the system logs in /var/log unless you specifically know what you're doing; the user-level logs give you the easy win here.

Step 3: Remove Time Machine Local Snapshots

macOS keeps local Time Machine snapshots on your startup disk so you can restore even when your backup drive is disconnected. They normally thin out on their own within about 24 hours, but if System Data is spiking and you need space now, you can remove them manually.

1. Open Terminal from Applications > Utilities.
2. List existing snapshots by typing tmutil listlocalsnapshots / and pressing Return. You'll see entries with dates.
3. Thin snapshots by freeing space. Run tmutil thinlocalsnapshots / 999999999999 4 to ask macOS to reclaim space by removing older local snapshots. macOS handles this safely — your real backups on the external drive are untouched.

Step 4: Clear Mail Downloads and Attachments

If you use the Mail app heavily, it caches downloaded attachments locally, and these can add up to several gigabytes. They live in a Mail downloads folder inside your Library and can be safely removed — Mail re-downloads attachments from the server when you open a message again.

Use Go to Folder and enter ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads. Review the contents and remove attachments you no longer need locally. Keep in mind that anything you have saved elsewhere (Documents, Downloads) is unaffected — this only clears Mail's local copies.

Step 5: Mop Up Other System Data

A few smaller sources round out the cleanup:

• Old disk images. Search your Downloads and home folder for .dmg files from apps you've already installed and delete them.
• Uninstalled app leftovers. When you remove an app, its Application Support data often stays behind in ~/Library/Application Support. Delete only the sub-folders for apps you've fully uninstalled.
• Restart to release swap. Virtual memory swap counts toward System Data. A simple restart frees it and lets macOS start fresh.
• Empty the Trash. None of the space you've freed is reclaimed until you empty the Trash — right-click the Trash icon and choose Empty Trash.

The One-Click Alternative: TrimyMac

The manual route works, but it means jumping between Finder, Terminal, and multiple Library folders, quitting apps, and being careful not to stray into folders you shouldn't touch. TrimyMac automates the whole thing. Its Smart Clean scans System Data, itemises the recoverable caches, logs, and junk, excludes anything protected, and clears it all in one pass — with a summary of exactly how much you reclaimed.

1. Download and open TrimyMac from the link below.
2. Run Smart Clean. It scans your disk, usually in under 30 seconds.
3. Review the categorised results — App Caches, Logs, Trash, and more — with per-item sizes.
4. Click Clean. TrimyMac removes what you selected and shows the space recovered. System caches and protected files are excluded automatically.