The Mac “Startup Disk Almost Full” Message and How to Fix It

Many Mac users will inevitably see the “Your startup disk almost full” error message show up in OS X, with a vague note to delete some files in order to make more space available on the Mac. While you can disregard the message for a little while, it will usually come back again shortly, and often soon after the startup disk will actually fill up and start causing problems in Mac OS X. Thus, if you see the “Your startup disk is almost full” error message in Mac OS X, you should address the issue before it becomes a problem.

We’ll cover some easy tips on how to quickly figure out what’s taking up the disk space on the Mac, as well as how to clear out storage capacity in order to resolve an almost full Mac.

It’s good practice to start a manual backup of the Mac with Time Machine before removing anything, this insures that if you accidentally delete the wrong thing you can get it back. As always, don’t delete files if you do not know what they are used for!

1: Get an Overview of What’s Eating Up Mac Startup Disk Space

Mac users can quickly see what’s taking up disk space through the system Storage summary, this can help lead you on the right path and give you an idea of what’s going on and where to look.

1. Open the  Apple menu and go to “About This Mac”
2. Choose the “Storage” tab (older versions of OS X need to click on ‘More Info’ before the Storage tab appears)
3. Review the storage usage to see what is eating up space and where you can focus your initial efforts on reclaiming some storage capacity

You’ll often see things that are immediately actionable in this list. Perhaps the “Backups” section is taking up many GB of space from locally stored iDevice backup files going back to the year 1400 BCE, you can delete old iPhone and iPad backups from iTunes easily and safely, just be sure you keep recent backups of devices, or use iCloud.

Sometimes you’ll discover your disk space has vanished to files you want to keep, however. A common example is discovering that “Photos” or “Movies” takes up many GB of local disk space but you don’t want to delete those files for obvious reasons. In those cases, you may want to offload them to an external hard drive for backups, a 5TB external drive on Amazon is affordable and will offer an abundant of disk space for such purposes.

Finally, many users discover that Other is taking up a fair amount of storage, this is usually stuff like downloads, caches, and whatever else doesn’t fall into the obvious media classifications. You can learn more about the “Other” storage space in Mac OS X and how to clear it out here.

2: Use Finder Search to Track Down Large Files

Did you know OS X can help you locate files with large sizes? Yes indeed, and using the Mac Search feature to find large files makes quick work of locating and deleting junk that is no longer needed but takes up space anyway. This is easy to use and quite helpful for remedying the “startup disk almost full” error message, here’s what you’ll want to do:

1. Go to any folder within the Mac Finder if you haven’t done so already, then hit Command+F to bring up the Finder Search feature
2. Change the search parameters to “This Mac”, then choose “File Size” as the primary search operator
3. Choose “is greater than” as the secondary search operator, then pick a file size to narrow large files by (for example, 1 GB, or 500 MB)

You can trash items directly from this search window by dragging them into the Trash or by hitting Command+Delete.

You’ll need to use your own discretion to determine whether or not you can delete some of the large files and items that turn up in the file size search, but don’t be surprised to come across large applications in OS X (you can delete most large apps if you don’t use them or need them), large .ipa files from iOS app backups, large disk image .dmg files, zip archives, and other items.

3: Investigate & Clear the Downloads Folder

The user Downloads folder can quickly accumulate all sorts of stuff you already used, no longer need, or is just outright unnecessary. This is often a primary location where the aforementioned large files accumulate over time as things are downloaded, installed, used, and then not removed. Sorting the directory in List view by File Size is often quite helpful in narrowing down the bloat:

Again, user discretion is going to be necessary to determine if you can or can’t delete stuff in the Downloads folder, so if something is important or gets a lot of use you won’t want to remove it, whereas old combo updates or disk images and zip archives that have been used or extracted already are often save to get rid of.

4: Empty the Trash to Actually Delete the Files

Empty the Trash if you haven’t done so already. This may sound obvious to some users, but it’s an often overlooked step. Just moving something to the trash doesn’t actually delete it, you have to empty the Trash, and the Trash can easily become a receptacle to the large files you trashed but haven’t actually removed yet.

Right-clicking (or a control+click) on the Trash icon and choosing “Empty Trash” is all that’s needed here.

5: Restart the Mac, then Check Storage Again

After you’ve cleared out some files and emptied the Trash, you should reboot the Mac. This is particularly true if it has been a while since the Mac has been restarted, as simply rebooting can often free up quite a bit of disk space by clearing out temporary items and the /private/var/ cache folders that can slowly accumulate to clutter up a drive. Rebooting also has the benefit of clearing out virtual memory, which takes up disk space, and sleep image files.

Go to the  Apple menu and choose “Restart”, when the Mac boots back up you can return back to the  Apple menu and choose “About This Mac” and the Storage tab to again review what your disk situation is like, chances are good at this point you will have tackled the space hogs and storage waste to do away with the “full disk” alert message on the Mac.

Still out of startup disk space? Start the process over again, you’ll need to remove more files, or you can try some of the other tips mentioned below.

More Tips for Freeing Up Storage Space on a Full Mac Disk

• You can uninstall Mac applications that you don’t need or use
• Messages attachments on the Mac can take up a surprising amount of space if you send and receive a lot of multimedia between contacts
• A more advanced method uses OmniDiskSweeper to track down disk space hogs by sweeping the drive by file size, this is not appropriate for casual Mac users however
• Delete old iOS backups in iTunes if you don’t need them, this is particularly relevant for old devices you may have backed up some time ago but no longer even own
• Manually deleting user caches in Mac OS X can free up a decent amount of space sometimes
• Follow some additional general tips for freeing up disk space on a Mac
• Advanced users can refer to reclaiming disk space with more complex methods
• Advanced users can delete default Mac apps like Mail and Safari, and even delete iTunes, but we do not recommend doing so unless you know exactly what you’re doing and have alternative apps setup already, removing system apps can cause all sorts of issues that average Mac users can find impossible to resolve

Something else to keep in mind that once you get that “startup disk almost full” error message on a Mac, the computer is going to be struggling to perform simple tasks like using virtual memory, downloading app updates, handling Photos and iCloud data, and much more, once it’s at that point the Mac will actually start running slower than it should be since OS X becomes occupied with trying to maintain itself given the storage constraints.

If you followed the above tips, you should be good to go at this point, but ultimately if you’re continuously running out of disk space you may need to upgrade the hard drive on the Mac in question, or at least get a large external drive to offload large files onto.

Have any other tips for tackling a full or almost full Mac startup disk? Let us know in the comments.