5 Things to Do When Your Mac Startup Disk Is Full

Robert Hunt
Last updated: Apr 28, 2023

Summary: In this article, you will learn what a startup disk is and how to clear it when it is full or almost full. 

If you use a Mac often, you may have encountered the warning that your startup disk is almost full. As a result of ignoring this message, your Mac performance drops, files can't be deleted, or even worse, your Mac won't start. 

Want to know how to fix a full Mac disk error? You've just come to the right place. In the following sections, we will take you through what a startup disk is, how to fix the Mac startup disk full problem, and, more importantly, how to avoid running out of disk space.

Startup Disk Full on Mac? Here's How to Fix It!

What Is Startup Disk on Mac?

The disk where your current macOS is installed is the startup disk. You can check your startup disk by clicking the Apple menu > System Preferences > Startup Disk.

Most Mac users have only one disk. Thus, the Macintosh HD is the default startup disk. If you are one of the few users who have 2 or more disks in Mac, you are free to choose which one to be your startup disk.

What Does It Mean When Your Startup Disk Is Full on Mac?

This message means that your primary disk has run out of storage capacity. This can be caused by too many files and applications stored on the disk. And what you need to do is free up disk space.

How to Check Startup Disk Space on Mac

When the system says that your startup disk is almost full, you need to pay attention to it. To check what files are taking up your startup disk space, follow the steps below:

  1. Click on the Apple icon in the upper left corner of your screen and choose About This Mac.
  2. Click the Storage tab, and you will see that the storage bar is divided into sections. Every colored section represents a category. The longer the section length, the more space that category takes up. If you have free space left, it should appear at the end of the storage bar.
  3. Click the Manage button above the storage bar to open the Storage Management Window, where you can see the size of every category.
Check Startup Disk Usage on Mac

Alternatively, you can also know how much storage space is used or unused with the Disk Utility.

How to Clear Your Startup Disk on Mac

By following the above steps, you know how much free disk space you have left. If you have a small amount of free space, you can use BuhoCleaner to quickly free up more disk space to avoid Mac performance downgrading. As a general of thumb, you need to keep at least 10GB of space to make sure your system is running properly.

DownloadFor macOS 10.10 and above
100,000+ Satisfied Users Worldwide

If unfortunately, your disk is full, you may get a message that your operation could not be completed. In this case, how can you free up disk space?

Don't worry. We have found some solutions for you.

1. Use Built-in Optimization Tools

Storage optimization tools are built into macOS Sierra and later. You can easily find them in the Storage Management window. Once you open the window, you will find 4 optimization recommendations, including Store in iCloud, Optimize Storage, Empty Trash Automatically, and Reduce Clutter. All you need to do is follow the recommendations to optimize your disk space.

Optimize Mac Storage

This method should solve your startup disk full problem. If not, move on to the next step.

2. Delete Files Bypass the Trash

How do you delete files on Mac? 99% of you may move them to the Trash. But actually, these files are still stored on your hard drive if you don't empty the Trash. When your startup disk is full, most likely, you will be unable to delete files or empty the Trash. Being the case, how can you reclaim some space? 

Don't worry, and you can delete files by bypassing the Trash. Here are 3 ways for you.

Clear Files via Shortcuts

Select the files you want to remove, hold down Command + Option + Delete keys, and click the Delete button.

Remove Files via Finder

Select the unwanted files, press and hold the Option key, and then click the File menu in Finder and Choose Delete Immediately.

Delete Files via Terminal

  1. Open Terminal via Spotlight or Launchpad.
  2. In the Terminal window, enter the command: sudo rm followed by a space.
  3. Drag the files you want to delete permanently into Terminal and press the Return key. 
  4. Enter your administrator password and press the Return key again.
Force Delete Files with Terminal
These 3 ways will delete files permanently, and files are not recoverable. We strongly recommend that you recheck files before deleting them.

3. Use the Safe Mode

If the above methods do not solve your problem, you can clear your disk in Safe Mode.

Safe Mode can solve almost all problems with Mac. When you boot your Mac in Safe Mode, unnecessary startup programs are disabled. Besides, Safe Mode will remove cache files and temporary files from your Mac, which frees up some space for you.

How to Start Mac in Safe Mode:

  1. Turn off your Mac.
  2. Press and hold the Shift key as your Mac starts up. 
  3. Release the keys when the login window appears.
  4. Log in to your Mac, maybe twice. You will see the Safe Boot words in the upper right corner of the login window.
  5. Delete files you don't want and restart your Mac. 

4. Move Files to An External Drive

There is another way you can use. That is to move files you don't currently use to an external drive. What you should do is find an external drive, connect it to your Mac, and then move files, especially the ones that take up a lot of space and you don't need for a while.

Also, you can store your unused files in the cloud and retrieve them from the cloud when you need them.

Related Article: Fix Copy and Paste Not Working on Mac – 10 Solutions

5. Use the macOS Recovery Mode

macOS Recovery Mode can fix disk-related problems. If you are experiencing abnormal operation due to a full disk, try using macOS Recovery Mode to repair and clean your disk.

Here are the steps:

  1. Close your Mac.
  2. Start your Mac and press and hold the Command + R keys immediately until the macOS Utilities window appears. 
  3. From the macOS Utilities list, select Disk Utility and click the Continue button.
  4. In the new window, click View > Show All Devices > First Aid > Run. ((If you don't see the Run button, click the Repair Disk button instead.)
Repair Disk Space in macOS Monterey

How to Avoid the Startup Disk Full Issue on Mac

It is unwise to start clearing disk space only after a full startup disk. You'd better clean your disk often.

There are many ways of freeing up disk space. You can refer to this article for detailed tips. In general, manually deleting unwanted files is tedious and time-consuming. If you don't have much time to do a manual junk cleaning, you can give BuhoCleaner ago. BuhoCleaner is one of the best Mac cleaning apps. Its noticeable features are flash junk file cleanup, unwanted app uninstallation, duplicate file and large file removal, memory release, startup program management, etc. With this handy tool, you can free up tens of gigabytes in just a few clicks.

DownloadFor macOS 10.10 and above
100,000+ Satisfied Users Worldwide

How to Use BuhoCleaner to Free up Space on Mac:

  1. Download and install BuhoCleaner on your Mac.
  2. Launch it, select a tool in the sidebar, and click the Scan button in the right column.
  3. When the scanning process is done, check the files you want to delete, and click the Remove button.
Quickly Clear Disk Space with BuhoCleaner


Now you know what to do when the startup disk is full-on Mac. To avoid running out of storage space again, always keep an eye on your available space. If you don't have enough storage space, don't forget to try BuhoCleaner. It can save you a lot of time and effort. 

Robert Hunt

I'm Robert Hunt, a tech-savvy fan with the love of all things Apple. As a hobbyist of gardening and meditation, I'm also a seasoned writer covering a wide array of Apple products, like iPhone, iPad, iOS and more.