How to Fix Startup Disk Full on Mac?

How to Fix Startup Disk Full on Mac (MacBook Pro/Air & iMac)?

“Your startup disk is almost full. To make more space available on your startup disk, delete some files.”

Inevitably, a full startup disk warning as such comes up on your MacBook Pro/Air, iMac, and Mac mini at some point. It indicates that you are running out of storage on the startup disk, which should be taken seriously because an (almost) full startup disk will slow down your Mac and in extreme cases, the Mac won’t start when the startup disc is full.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

In this post, we will cover every question you may have about the full startup disk on Mac, including:

What is Startup Disk on a Mac?

Simply put, a startup disk on a Mac is a disk with an operating system (such as macOS Mojave) on it. Usually, there is only one startup disk on a Mac, but it is also possible that you have divided your hard drive into different disks and get multiple startup disks.

Just to be sure, make all disks show up on your desktop: click Finder on the Dock, select Preferences, and check “Hard disks”. If multiple icons are showing up on your Mac, it means that you have multiple disks on your Mac. However, you only need to clean the startup disk that your Mac is currently running on, which is the one that has been selected on System Preferences > Startup Disk.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

What Does It Mean When Your Startup Disk Is Full?

When you are seeing this “your startup disk is almost full” message, it means that your MacBook or iMac is running on low space and you should clear your startup disk as soon as possible. Or the Mac will be acting weirdly because there is not enough storage space, such as getting intolerably slow, and apps crashing unexpectedly.

To find out what’s taking up space on your startup disks and make room on the startup disk immediately. If you don’t have time to delete files from startup disks one by one, you can ignore the rest of the article and download MobePas Mac Cleaner, a disk cleanup tool that can show what’s taking up space on the disk and remove unneeded large files, duplicate files, system files all at once.

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How to See What’s Taking up Space on Mac Startup Disk?

Why is my startup disk getting almost full? You can find the culprits by visiting About this Mac.

Step 1. Click on the Apple icon and select About this Mac.

Step 2. Click Storage.

Step 3. It will show how much storage has been used in your startup disk by which kind of data, such as photos, documents, audio, backups, movies, and others.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

If you are running on macOS Sierra or higher, you can optimize storage on Mac to free up space on the startup disk. Click Manage and you can have all the options to optimize storage. The solution is to move your photos and documents to iCloud, so make sure you have enough iCloud storage.

How to Clean Startup Disk On MacBook/iMac/Mac Mini?

As you have figured out what is taking up space on the startup disk, you can start to clean the startup disk. If you are looking for a convenient way to clear disk space on a Mac, MobePas Mac Cleaner is recommended. It can find all junk files on the startup disk and clean them in one click.

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mac cleaner smart scan

For example, if you find that photos are taking up too much space on the startup disk, you can use Similar Image Finder and Photo Cache on MobePas Mac Cleaner to clear the startup disk.

To clean system storage on the startup disk, MobePas Mac Cleaner can delete System Junk, including cache, logs, and more.

clean system junk files on mac

And if it is apps that occupy the most space on the startup disk, MobePas Mac Cleaner can completely remove unwanted apps and related app data to reduce system storage on Mac.

MobePas Mac Cleaner can also find and delete large/old files, iOS backups, mail attachments, trash, extensions, and many other junk files from the startup disk. It can make the startup disk almost fully gone right away.

Download the free trial version of MobePas Mac Cleaner to have a try right away. It works with macOS Monterey/Big Sur/Catalina/Mojave, macOS High Sierra, macOS Sierra, OS X El Capitan, and more.

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Also, you can clean the startup disk step by step manually, which will take a longer time and more patience. Read on.

Empty the Trash

This may sound silly, but when you drag a file to the Trash, it is still using your disk space until you empty the file from the Trash. So the first thing you should do when your Mac tells you the startup is almost full is to empty the Trash. Before you do so, you should really make sure that all files in the Trash are useless. Emptying Trash is simple and can free up space on your startup disk right away.

Step 1. Right-click the Trash icon in the Dock.

Step 2. Select “Empty Trash.”

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

Clean up Caches on Mac

A cache file is a temporary file created by apps and programs to run more quickly. Caches that you don’t need, for example, caches of the applications that you no longer use, can fill up the disk space. So follow the steps below to remove some caches that are needed, and Mac will automatically recreate them in the next reboot.

Step 1. Open Finder and select Go.

Step 2. Click on “Go to Folder…”

Step 3. Type in “~/Library/Caches” and hit Enter. Delete all cache files that are large or belong to the application that you no longer use.

Step 4. Again, type in “/Library/Caches” in the Go to Folder window and hit Enter. And then remove the cache files.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

Remember to empty the trash to regain disk space.

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Delete Old iOS Backups and Updates

If you often use iTunes to back up or upgrade your iOS devices, there may be backups and iOS software updates that are taking up your startup disk space. Find the iOS backup update files and get rid of them.

Step 1. To locate iOS backups, open “Go to Folder…” and enter this path: ~/Library/Application Support/MobileSync/Backup/.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

Step 2. To locate iOS software updates, open “Go to Folder…” and enter the path for iPhone: ~/Library/iTunes/iPhone Software Updates or the path for iPad: ~/Library/iTunes/iPad Software Updates.

Step 3. Clean all the old backups and update the files you have found.

If you are using MobePas Mac Cleaner, you can click its iTunes Junk option to easily get rid of all backups, updates, and other junk that iTunes has created altogether.

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Remove Duplicate Music and Videos on the Mac

You may have many duplicate music and videos on your Mac that take up extra space on your startup disk, for example, the songs that you have downloaded twice. iTunes can detect duplicate music and videos in its library.

Step 1. Open iTunes.

Step 2. Click the View in the Menu and select Show Duplicate Items.

Step 3. You can then examine the duplicate music and videos and remove those you don’t need.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

If you need to detect duplicate files of other kinds, such as documents, and photos, use MobePas Mac Cleaner.

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Remove Large Files

The most effective way to free up space on the startup disk is to remove large items from it. You can use Finder to quickly filter larger files. Then you can directly delete them or move them to an external storage device to free up space. This should quickly fix the “startup disk almost full” error.

Step 1. Open Finder and go to any folder you like.

Step 2. Click “This Mac” and select “File Size” as the filter.

Step 3. Enter a file size to find files that are greater than the size. For example, find files that are larger than 500 MB.

Step 4. After that, you can identify the files and remove those you don’t need.

Startup Disk Full on MacBook Pro/Air, How to Clean Startup Disk

Restart Your Mac

After the above steps, you can now restart your Mac to make the changes take effect. You should regain a large amount of free space after all the deleting and stop seeing “the startup disk is almost full.” But as you continue to use the Mac, the startup disk may get full again, so get MobePas Mac Cleaner on your Mac to clean up space from time to time.

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How to Fix Startup Disk Full on Mac?
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