Restarting your Mac is one of the simplest steps you can take to free up storage space – and it works automatically. When you reboot, macOS automatically purges certain temporary files and memory caches, effectively reclaiming some of the “purgeable space” that has been earmarked for removal. It may seem too basic to be effective, but this built-in housekeeping can resolve minor performance issues and contribute to a smoother overall experience.
What is purgeable space?
Purgeable space refers to files that macOS identifies as safe to remove when the system needs additional storage, but which it does not delete until it is under pressure. The concept is central to Apple’s Optimised Storage feature, introduced with macOS Sierra. These files are generally old, have not been used for some time, or are already synced with iCloud, meaning the local copy can be removed without loss. The categories include system caches and temporary files (such as sleep images and swap files), iCloud-synced content (Desktop and Documents folders if “Store in iCloud” is enabled), Time Machine local snapshots (hourly backups stored on the startup disk itself), downloaded media and purchased content that can be re-downloaded, and rarely used fonts or dictionaries.
You can check how much purgeable space your Mac holds in the Storage Settings. On macOS Ventura and later, go to Apple menu > System Settings > General > Storage. On earlier versions, find it under Apple menu > About This Mac > Storage. In either case, purgeable space is indicated by a section marked with white and grey stripes. Disk Utility (Applications > Utilities) and Get Info on the startup drive also display purgeable space as part of the “Available” figure. It is important to note that purgeable space is not the same as truly free space – the files still reside on the drive until macOS reclaims them automatically, usually when the system is running critically low on storage. Restarting can sometimes trigger that process.
Methods to clear purgeable space
Several approaches exist for freeing up this space, ranging from turning on system features to using manual or automated tools. The choice depends on your comfort level and how much control you want.
Enable Optimised Storage
Apple’s Optimised Storage feature can be toggled on or off at any time. When enabled, it automatically manages several of the categories mentioned above – offloading iCloud-synced content, removing watched movies and TV shows, and clearing temporary files. This is a set-and-forget method that runs in the background and can save a significant amount of space over time. However, accessing iCloud-synced files after they have been purged requires an internet connection, and the free 5GB of iCloud storage may not be sufficient for heavier users.
Disable Time Machine backups (with a caution)
Time Machine local snapshots are a major component of purgeable space. The original advice suggests disabling Time Machine backups entirely to reclaim that space. However, research indicates that this is generally not recommended. Local snapshots are automatically deleted by macOS when space is needed or when they exceed 24 hours old. Disabling the entire backup system removes a critical safety net for data recovery. A less drastic approach is to let macOS manage these snapshots automatically, or, if you are an advanced user, to use the Terminal utility tmutil to list and delete individual snapshots. But even then, new snapshots will be created, so this is a short-term fix.
Clear cache files
Cache files are temporary data stored by macOS and applications to speed up performance. Clearing them can free up space, but it carries risks. Deleting cache files while an application is running can cause it to misbehave or crash; clearing essential system caches may cause instability; and website and app caches will rebuild, leading to temporary slowdowns. The safest manual method is to quit all running applications, then open Finder and navigate to ~/Library/Caches (via Go > Go to Folder). Inside each folder, delete the contents – not the folders themselves. For system caches, you may need to go to /Library/Caches, which can require an administrator password. Browser caches can be cleared via each browser’s settings: in Safari, enable the Develop menu from Advanced preferences and select “Empty Caches”; in Chrome, go to Settings > Privacy and security > Clear browsing data and select “Cached images and files”; in Firefox, go to Settings > Privacy & Security > Clear Data and tick “Temporary cached files and pages.”
Because manual cache clearing is risky and time-consuming, many users prefer dedicated Mac cleaner tools such as CleanMyMac X, DaisyDisk, OnyX, CCleaner for Mac, Macube Cleaner, Cleaner One Lite, or MacKeeper. These applications provide a user-friendly interface to scan for junk files, duplicate files, large files, and app leftovers, and can automate deletion. While generally safe, it is wise to use reputable software and understand what each tool is doing.
Use the Terminal (the most complex method)
For those comfortable with command-line tools, the Terminal offers a powerful – but dangerous – way to force the system to purge space. This method is only recommended if you know exactly what you are doing, as incorrect commands can permanently delete essential files and destabilise your Mac. The process involves creating a large, deliberately wasteful file to push the system into a critically low disk state, which triggers macOS to purge purgeable files. Here is the step-by-step procedure described in the original article:
First, open Terminal and type mkdir ~/largefiles, then press Return. This creates a folder named Largefiles in your home directory. Next, paste the command dd if=/dev/random of=~/largefiles/largefile bs=15m and press Return. This writes random data to a file called largefile in blocks of 15 megabytes. Let it run for a few minutes, then press Ctrl+C to stop the process. Then paste cp ~/largefiles/largefile ~/largefiles/largefile2 and press Return to duplicate the file. You can repeat this command, changing the filename (largefile2, largefile3, etc.) each time. Stop when you see a warning that the disk is critically low. Finally, paste rm -rf ~/largefiles/ and press Return to delete the largefiles folder and all its contents. Empty the Trash afterwards.
This technique is complex and time-consuming, but it forces the system to purge its purgeable space as a side effect of running out of room. A less aggressive Terminal approach is to use commands like sudo purge to clear active memory and disk caches, or sudo rm -rf ~/Library/Caches/* to delete user cache files (again, with the risk of instability). Always back up your Mac before using Terminal for storage management, as files deleted with rm are permanently gone and do not go to the Trash.
Use a Mac cleanup tool
The simplest and safest method for most users is to use a dedicated Mac cleanup tool. These applications automate the process of identifying and removing purgeable files, cache junk, old downloads, and app leftovers. CleanMyMac X, for example, offers a “Smart Scan” that combines junk file removal with malware protection and system optimisation. DaisyDisk provides a visual map of disk usage to help you spot large files. OnyX offers deep system configuration and maintenance scripts for advanced users. Tools like Cleaner One Lite and Macube Cleaner also offer big file scanners and duplicate finders. The main advantage is saving time and effort while reducing the risk of accidental deletion.
Restart your Mac
As noted at the start, a simple restart can trigger macOS to automatically purge temporary files and memory caches. While it may not clear all categories of purgeable space, it is a zero-effort step that can resolve minor performance glitches and free up a modest amount of storage. It is often overlooked, but it is worth trying before resorting to more involved methods.
Benefits of purging purgeable space
Clearing unnecessary files from your Mac improves overall performance and delivers a more responsive experience. The drive has more room for active processes, applications launch faster, and the system is less likely to display “low disk space” warnings – even if significant purgeable space existed beforehand. Automated tools and the Optimised Storage feature make the process convenient, while manual methods like Terminal give power users fine-grained control. Despite the complexities, the payoff is a smoother-running machine that makes the most of its available storage. No single method is perfect, but by understanding what purgeable space is and how to manage it, you can keep your Mac running at its best.
