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One day, you’re using your Mac like normal when suddenly you get the dreaded error message saying, “your startup disk is almost full.” This might come with a host of other issues like slow performance, glitchy applications, failed downloads, and the inability to install updates.

Having enough space on your startup disk is crucial to your Mac’s functionality. So how can you get some much-needed space on your startup disk? In today’s article, we’ll dive deep into why the “startup disk almost full” issue occurs and some potential remedies we can use to fix it.

What Is a Startup Disk on Mac?

The startup disk is a vital component of your Mac. This drive is where your operating system and all of your software live. Your pictures, documents, music, and other projects also call the startup disk home. Depending on your startup disk’s capacity, you might wind up in the unfortunate position of running out of space before long.

While some Macs offer upgradeable storage drives, many do not. As a result, your primary startup disk represents all of your Mac’s internal storage.

If you need to store vast amounts of files, you can always turn to a cloud storage service like Google Drive or DropBox, or even use an external backup device like a USB flash drive or external hard drive. However, smooth system performance relies on your startup disk.

Critical operating software resides on your startup disk and accounts for all the primary functions of your computer. Under normal conditions, your operating system writes and deletes files on your drive as it needs to.

Temp files, cache files, and system files expand as the system requires. However, if your startup disk fills up, macOS won’t be able to perform its primary functions, leaving your Mac in a potentially problematic state.

How to See Your Startup Disk Usage

The first step to fixing the “startup disk almost full” issue on Mac is determining how much space you have at your disposal. A MacBook with a 128 GB drive will run low on space faster than a system with a larger drive, like 512 GB or 1 TB. Checking your startup disk usage is a straightforward process and only takes a few seconds.

Step 1: Select About This Mac

how to fix startup disc almost full on mac
Selecting About This Mac.

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Select About This Mac from the options under the Apple Icon along the top of your Mac’s screen. This will open a window displaying all of the information about your Mac, such as model year, processor, RAM, and graphics. Most importantly, this area gives you a detailed peek into your disk usage.

Step 2: Click on Storage

How to fix Startup Disc Almost Full on Mac
Locating the Storage tab.

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To fully view your storage usage, select the tab marked Storage from the options along the top. As you can see, your Mac gives you a full breakdown of your storage capacity and which files are taking up the most space.

You will see files marked as Documents, Pictures, and Videos. All of these can be safely moved offsite to an external hard drive or cloud backup. Files marked System are the only file types that are off limits since your Mac needs these to operate correctly. However, even system files can be reduced with a few optimization tips.

Tip 1: Move Your Files to iCloud

The cloud refers to offsite data storage services like DropBox, Google Drive, and iCloud. These services allow you to log in and upload your files and folders no matter where you are in the world. You can even sign into your account via multiple computers to keep backups of all of your files. 

For simplicity’s sake, iCloud is the most user-friendly suggestion for using a Mac. Since the application is built into the operating system, you don’t have to worry about additional setup or configuration.

All you need to do is make sure iCloud is enabled. You must ensure you are signed into your iCloud account on your Mac with your Apple ID.

Step 1: Sign in to iCloud

How to fix Startup Disc Almost Full on Mac
Finding the Sign in option within System Preferences.

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Locate the System Preferences from within your dock and open it. From here, locate the Apple ID options near the top of this window and sign in.

Step 2: Optimize Mac Storage

How to fix Startup Disc Almost Full on Mac
Optimizing storage.

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Once you’ve signed in, find the iCloud options from the sidebar, then open the iCloud Drive menu. Here, you’ll see all of the available options for syncing your files with iCloud. You can back up pictures, documents, and videos.

Additionally, you can sync your applications and contacts so you don’t lose anything. Make sure to check the box marked Optimize Mac Storage.

Tip 2: Clear Out Your Trash

The Trash is often one of the guilty culprits for taking up valuable storage space. You might not suspect the Trash since it hides in a far corner of your Dock, but it can often hide some of your most extensive unused files. Worse, you won’t even realize these files are consuming precious space until you check. 

Even after you’ve moved an item to the Trash, it remains. The quickest way to ensure that your Trash doesn’t take up space is to empty it as soon as you put something in it. To do this, hold down the Control key on your keyboard while tapping on the Trash icon in the dock. Next, click Empty Trash to remove any files that are inside.

How to fix Startup Disc Almost Full on Mac
Finding the Manage option in Mac’s built-in storage optimization tool.

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Another way to access the Trash folder is through Mac’s built-in storage optimization tools. These are located under the About This Mac window we’ve accessed previously. Simply follow the steps outlined when we checked the storage capacity. Once you arrive on this screen, hit Manage.

How to fix Startup Disc Almost Full on Mac
Selecting Trash from the pop-up menu.

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A window will pop up with a few recommended options. Select Trash from the options along the left and review individual trash items or empty the entire folder. Additionally, ensure your Trash is set to Empty Trash Automatically after 30 days.

Tip 3: Remove Unwanted Applications

While on this window, you should review your application list to ensure that nothing takes up too much space. Software and programs can be notoriously resource-hungry, and larger apps can be guilty of consuming valuable startup disk space. Removing apps that you don’t use anymore will let you use those precious few gigabytes.

How to fix Startup Disc Almost Full on Mac
Clicking on Applications.

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Have a look at the Applications selection from the options in the left sidebar. As we can see, macOS tells us precisely how much storage capacity the application library takes up.

Click on this list and review your apps. Remove any that you no longer need. You don’t need to worry about accidentally deleting system apps since macOS prevents you from doing this as a safety precaution. 

Tip 4: Clear Your Downloads Folder

Your downloads folder is where your Mac stores all of the application installers, music files, and document downloads that you make while using your Mac. Whenever you download an app from the internet, its installer files remain in your Downloads folder. As a result, the Downloads folder can get cluttered beyond comprehension.

Fortunately, clearing out your Downloads folder is a straightforward process that only takes a minute. To get started hit Go from the options along the top of your display and click Downloads.

How to fix Startup Disc Almost Full on Mac
Going into the Downloads folder.

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A window will appear, showing all of your downloads. Many files are unnecessary, especially installers for applications. Other files, like pictures and documents, should be moved to another folder, like your iPhoto Library or Documents folders.

To clear all of these files immediately, hold the Command and A keys simultaneously to select everything. Next, drag the group of files to the Trash bin.

Alternatively, you can right-click on the files and select Move to Trash. Remember to clear out the Trash when you are done, and the Downloads folder will no longer bother you for space.

Tip 5: Clear Your System Cache

If your Mac still prompts you with the dreaded “startup disk almost full” message after clearing out your Trash and Downloads folder and removing unnecessary applications, you can try other methods. The cache is often guilty of consuming too much space on your startup disk.

Even so, the cache is a vital part of almost any application on your Mac. As the name suggests, your Mac uses these files to improve performance with frequently accessed apps and files. However, leftover cache files can build up and consume more space than necessary. Clearing your cache is a handy way to regain some space.

Similar to the last tip, you’ll select Go from the options on the top of your display. From here, hit Go To Folder. Mac will prompt you for a directory. Input the following address to access your cache files:

~/Library/Caches

Next, click Go, and your Mac will take you to the directory containing your cache files. A window with all of your Mac’s cache folders will appear next. The only time-consuming part is going into each directory and removing the files. 

Many third-party apps exist to speed up this process. For example, the app CleanMyMac X has a built-in utility for accessing and regularly removing excess cache files. The only downside to this solution is the price. It can make things easier if you don’t mind paying a few dollars for an all-in-one app to handle maintenance. However, you can still handle your cache folders and junk files quickly enough if you’re on a tight budget.

Make Sure to Restart Your Mac

If you don’t notice any increase in free storage space after clearing out your Downloads, taking out the Trash, and removing Cache files, you might have to restart your Mac. By restarting, your Mac clears out any temporary files and finalizes the deletion of cache and junk files.

The next time your Mac boots up, recheck your storage. You should not see the “startup disk almost full” warning anymore.

How To Fix Startup Disk Almost Full on Mac FAQs (Frequently Asked Questions) 

Why is the startup disk almost full on Mac?

Your startup disk can fill up if you have too many unnecessary applications, cache files, Trash files, or downloads.

How much space do you need on Mac? 

Mac requires less than 30GB for your operating system. However, programs and files can quickly eat through this space. You should have at least 128GB to 256GB to comfortably enjoy your Mac without frequently running low on space.

Can you add storage to Mac? 

Yes. You can easily plug in an external hard drive or USB device for more storage space. Additionally, many older Macs offer expandable solid-state drives for increasing your capacity.

Why is Mac running slow? 

Your Mac may run slow if it runs low on storage space or RAM. Additionally, your Mac may slow down due to software issues, old updates, or malfunctioning background apps and services.

Why is my disk full for no reason? 

While it may seem like your disk is full for no reason at all, you can usually pinpoint the lack of space to a few factors. You may have unnecessary apps, files, or system junk. You might also have too many files in your Trash bin or Downloads folder.

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