What to Do If Your Mac Startup Disk Is Full

Uh-oh: Your Mac is taking forever to boot up. And once it is booted, it’s slower than molasses. A slow-performing Mac may be due to limited startup-disk or hard-drive space. Fear not: We here at RenewedMacs can help you diagnose and solve this common problem. Continue reading to discover a few common fixes, and what to do if your startup disk just can’t be saved.

The Startup Disk and Why It Gets Full

Fixing a problem should start with understanding how it started in the first place. The startup disk is essentially your computer’s hard drive. It contains the operating system — the set of files necessary for your computer to run — and is extremely important.

Once your startup disk gets to about 85% full, your Mac will start acting up and you will most likely see the message “Your startup disk is almost full.” This means that you’ll soon run out of space entirely and that the disk is going to perform slowly.

Believe it or not, Macs create “junk” regularly. (It’s not just a preoccupation for Windows users.) The Mac’s system, like all other operating systems, depends on creating temporary files, caches and backups to function properly. However, after this data has done its part, it sits there in your Mac’s startup disk, taking up space for no apparent reason and slowing your system down.

The good news is that it’s extremely simple to remove these useless files, freeing up gigabytes and fixing your full-startup-disk problem, without affecting any of your personal data.

How to Clean Your Mac’s Hard Drive

The good news is that you won’t need to buy and install additional software to clean up your hard drive. In fact you should stay away from apps that market themselves as cleaners/keepers, as some are often hosts to malware and other nasties that might negatively affect your device (never download MacKeeper). Here are a few easy things you can do to clean your Mac’s hard drive manually. 

Empty the Trash

This is perhaps the easiest way to free up disk space. Click on the Trash icon in the lower right-hand corner, and once it’s launched, click the gray Empty button in the upper-right hand corner.

Clear the Cache

This is an oldie but a goodie. (Former Windows users probably remember this one.) A cache is a temporary file that duplicates information previously processed by your computer, so when you open or access the file in the future, it loads more quickly. Of course, as these cache files pile up, they do the opposite: They actually slow your computer down.

To remove app cache files and clean up a startup disk, follow these steps:

  • Navigate to Finder, then Go, then Go to Folder.
  • Type in ~/Library/Caches (yes, you need the tilde ~).
  • Go into each folder separately and delete the files inside each.
  • Now do the same for /Library/Caches (without the ~).

It’s important to go folder by folder. If you feel that a file is something important or system-related, then do not delete it.

After completion, remember to empty the Trash.

Remove iTunes Backups

Every time you update iTunes, the update comes with a backup of your entire iTunes library. That means that with every update, you end up with a ton of backups when you really only need one.

To find and delete old iTunes backups so you can free up space, follow these steps:

  • Navigate to Finder, then Go, then Go to Folder.
  • Type in ~/Music/iTunes/Previous iTunes Libraries.
  • Sort the files by date and delete all but one or two of the most recent backups.

Again, empty the Trash.

Uninstall Unused or Unneeded Applications

After a few years of using your Mac, you probably have several apps you do not use or need anymore. Go to your Finder, then Applications. Sort through them, move to Trash, then visit the Trash (again) to fully delete.

How to Keep Things in Tip-Top Shape Moving Forward

It’s easy: Clear space on your Mac from time to time. This good habit will keep it spick-and-span so you’re no longer afraid of the Mac “startup disk full” message.

Here is what you can do on a regular basis:

Empty the Trash

Again, click on the Trash icon and empty it regularly.

Delete DMG Files

After you download a new application, the new app will automatically be moved to your Applications folder. However, in the Downloads folder will be a DMG file that is usually of the same (large) size, and it can be deleted. A DMG file is a mountable disk image used to distribute software to the macOS operating system — something of a holdover from the days of downloading software from CD-ROMs (remember those?). You can get rid of these large DMG files regularly, or immediately after install.

Consider an External Drive or the Cloud

As your photos, videos and iTunes content accumulates, your startup disk gets more and more full. Consider moving this content to the cloud and access it on an as-needed basis. iCloud is the easiest to use as an affordable solution offered by Apple.

Install DaisyDisk to Clean Up and Organize Files

If this is all too much to keep track of, or you’re still experiencing some stubborn issues, consider installing a utility app like DaisyDisk. DaisyDisk displays your disk storage in real-time, so you can see what’s taking up so much space. System files are protected, and you can decide which files to delete.  

Like we mentioned previously, DO NOT install other software marketed as a Mac “cleaner,” as these can do more damage to your computer. In fact, some of these cleaners, such as MacKeeper, are known malware!

When It’s Simply Time to Replace Your Mac

At some point, you may simply have to bite the bullet and purchase a new, or new-to-you Mac. If you decide to save some cash by going down the renewed route, consider a source with years of experience in Apple hardware and world-class customer service. RenewedMacs works exclusively with Apple products (all of which are sourced from our sister site, SellYourMac), and our team can advise on the best solution for a renewed system.





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