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Mac Startup Disk Full — Free Up Space and Identify Large Files

Errordisk

Overview

Fix Mac 'Your startup disk is almost full' warning by identifying large files, clearing system caches, managing Time Machine snapshots, and optimizing storage.

Key Details

  • macOS needs 10-15% free space on the startup disk for virtual memory, swap files, and updates
  • System Data (shown in About This Mac > Storage) includes caches, logs, and Time Machine local snapshots
  • Time Machine local snapshots can consume 50GB+ and are not easily visible in Finder
  • Xcode, Docker, and virtual machines are common hidden space consumers in developer setups
  • iCloud 'Optimize Mac Storage' can free up space by keeping only recent files locally

Common Causes

  • Large files accumulated in Downloads, Desktop, or Documents folders
  • Application caches growing excessively (Xcode, browsers, Spotify)
  • Time Machine local snapshots consuming space while backup disk is disconnected
  • Deleted files still in Trash consuming disk space
  • macOS system updates downloaded but not yet installed

Steps

  1. 1Check storage: Apple menu > About This Mac > Storage (or System Settings > General > Storage on newer macOS)
  2. 2Use the storage management tool: click Manage in the Storage view for category-by-category cleanup options
  3. 3Empty Trash: Finder > Empty Trash (or right-click Trash icon > Empty Trash)
  4. 4Delete Time Machine local snapshots: tmutil listlocalsnapshots / then tmutil deletelocalsnapshots <date>
  5. 5Clean application caches: ~/Library/Caches/ — delete folder contents (not the folders themselves)
  6. 6Enable Optimize Mac Storage for iCloud: System Settings > Apple ID > iCloud > Optimize Mac Storage
  7. 7Use a tool like DaisyDisk or GrandPerspective to visualize disk usage

Tags

startup-diskdisk-fullstoragefree-spacecleanup

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mac-disk-full-startup-disk

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Frequently Asked Questions

System Data includes caches, logs, Time Machine local snapshots, Spotlight index, and iOS device backups. Delete Time Machine snapshots and clear caches to reduce it.