Macs rarely cause any issues for users when it comes to errors. Any bugs and glitches tend to resolve themselves with a simple system restart.
One exception is the startup disk full Mac message, which can negatively affect your Mac’s performance. This error means that the accumulation of outdated files, system logs, app caches, and other data has exceeded the storage limit recommended by macOS.
These files are difficult to find and delete. Moving a few of them to the Trash won’t do much. What your disk full Mac needs is a serious cleanup.
By keeping the Mac startup disk tidy in the first place, you can avoid numerous issues that hamper performance. In this article, we provide step-by-step instructions on how to avoid the "startup disk full" problem. Spoiler: Moving files to Trash isn’t going to fix it.
What is a startup disk on Mac?
A startup disk is your main hard drive on Mac, from which the macOS starts up (hence the name). For the majority of users, startup disk — Macintosh HD — is the only hard drive on Mac.
It’s possible to partition your startup disk into a few instances and use additional external hard drives to store files. In that case, the startup disk is the one that boots up the macOS.
What does "Your disk is almost full" message mean?
When your hard drive is nearing its capacity, you’ll get a notification saying that "your startup disk is almost full."
The Mac startup disk full message means that all your files are taking up over 85% of the startup disk’s space, which is the recommended limit. If you disregard the notification and continue adding files, your Mac performance is going to be negatively affected, causing scratch disk errors and more.
How to check disk space on Mac
If you get the Mac startup disk almost full error, the first thing you should do is check what’s taking up all the space. Then you can see what can be done to optimize your Mac.
To check storage on Mac:
- Open System Settings
- Go to General ➙ Storage
You’ll see a visual graph at the top, breaking down the types of files taking up space on your Mac, from iCloud Drive to apps to macOS. If this graph is approaching or exceeding 85% of the storage capacity, you need to take immediate actions to resolve the situation to avoid slowing down your Mac or losing unsaved files.
Scrolling down to the next section, you’ll see recommendations and a full list of categories. If you click the info icon next to each category, you’ll get more information and possible actions to decrease the space it uses.
How to fix the startup disk full error
Apple doesn’t make it easy to delete hidden system folders and other junk. And there are likely gigabytes of those files on your Mac now, from old app caches to iPhone backups.
Here’s an easy checklist to go through when you find your startup disk full.
Empty the Trash
If you never empty the Trash, the files you delete don’t disappear from your Mac — they relocate (albeit in a more compact form). Emptying the Trash gets rid of those files forever and frees up space on your startup disk.
To empty the Trash:
- Click the Trash icon in the Dock
- Click Empty
Another option is to right-click the Trash icon and select Empty Trash.
To not empty the Trash manually all the time, you can enable automatic file deletion from the Trash after 30 days:
- Open Preferences (Command + ,) in Finder
- Switch to the Advanced tab
- Check “Remove items from the Trash after 30 days”
Delete app caches
Every app you’ve ever installed on your Mac leaves behind system-related files and user preferences that stay even once you get rid of the app itself. Over time, those files, referred to as caches, tend to accumulate and take up significant space on your startup disk.
It’s hard to delete all the caches you don’t need since it requires going into system folders with no clear indicators, but you can start:
- From the Finder menu bar, select Go ➙ Go to Folder (Shift + Command + G)
- Type ~/Library/Caches and press Return
- Look for any app you don’t have anymore and don’t need in the future
- Moves its folder to the Trash
For a more complete cleanup, you need to use an automated tool like CleanMyMac X.
CleanMyMac X solves all the problems with getting rid of useless system files without any manual sorting. This is a powerful tune-up app for your Mac, featuring tools to free up space, remove malware, improve privacy, optimize system processes, uninstall apps, and much more.
To delete app caches with CleanMyMac X:
- Launch the app
- Go to System Junk ➙ Scan
- Review Details
- Check User Cache Files (and optionally any other categories)
Delete old downloads
The Downloads folder in Finder is the default place for all files downloaded from the internet. That’s why Downloads tend to accumulate files over the years, which eventually slow down your Mac.
To clean up the folder quickly, open it through Finder, right-click, and group files by size. Start looking through files from the top, deleting the ones you don’t need.
Back up large files
No matter how many files you don’t need you delete, if the files you do need (sometimes) occupy lots of space, you’ll have an ongoing startup disk full Mac problem.
The solution is to back up large files that you don’t use all the time and move them off your Mac. They will remain accessible from the cloud or external storage when needed.
The easiest thing to do is enable iCloud syncing to get all the iCloud Drive files to the cloud. It’s a good idea to sync your files across your devices and the cloud. However, iCloud is not a backup solution — it’s a syncing solution. If you delete your files from your Mac, they will be deleted everywhere else.
A proper backup solution that keeps your files safe is an app like Get Backup Pro.
Get Backup Pro allows you to pick the type of backup you want, from simple copy to incremental to versioned. You can back up selected files and folders to an external drive or sync them between two Macs. There’s an option to schedule backups and even make them bootable (for installing the macOS itself).
Delete duplicate photos
With iPhones in our pockets anywhere we go, it’s easy to take photos, and they tend to accumulate on our Macs much faster than we can review and delete the ones we don’t need.
Manual solutions here are not feasible. That’s why having a duplicate finder and remover on your Mac is a must.
Gemini is the most capable duplicate finder on the market. It scans any folder on your Mac (or your whole Mac) and finds any duplicate files, from videos and photos to documents and presentations. Even better, Gemini finds similar files, such as photo variations or document drafts, and suggests them for deletion. Then you can free up space with a single click.
To delete duplicates with Gemini:
- Launch the app
- Click the plus icon and choose a folder to scan
- Scan for Duplicates
- Review Duplicates
- Delete any copies you don’t need
Remove old system and user logs
System and user logs are text-based files that record various events going on with macOS and third-party apps. While they don’t tend to take up a lot of space, it’s a good practice to delete them once in a while.
To manually remove system and user logs:
- In Finder, choose Go ➙ Go to Folder (Shift + Command + G) from the menu bar
- Type ~/Library/Logs and hit Return
- Delete the logs you know you don’t need
A faster and safer way to delete logs is with CleanMyMac X:
- Launch the app
- Select System Junk and Scan
- Review Details
- Check System Log Files and User Log Files
Uninstall unused apps
Apps are among the top consumers of disk space on Mac. If you don’t keep track of them, they might quickly become the reason your startup disk is almost full.
It’s easy to delete apps on your own. Open the Applications folder and move the apps you don’t need to Trash. The problem is that most apps have auxiliary files saved in other places around your Mac which you don’t want to leave behind.
The way to properly uninstall apps is with CleanMyMac X:
- Launch the app
- Go to Uninstaller from the sidebar
- Select any apps you want to delete
Delete unused languages
Lots of apps on your Mac contain language localizations you likely don’t use. And they all take up additional space. Depending on how many apps you have installed, this category can swell up to a few gigabytes.
To clean up unused languages manually:
- Open the Applications folder (Shift + Command + A)
- Right-click on any app and select Show Package Contents
- Go to Contents ➙ Resources
- Delete files or folders for the languages you don’t need (they have with the .lproj extension)
Repeating the above for all the apps on your Mac will take a lot of time. Instead, you can delete all the unused languages in one click with CleanMyMac X:
- Open CleanMyMac X
- Click System Junk ➙ Scan
- Review Details
- Check Language Files
Clean your Desktop
Desktop plays a special role on your Mac. Think of it as a folder that’s always open. Every time you look at your Desktop, your Mac has to refresh it to make sure it displays the most up-to-date information. That’s why the fewer files you keep on your Desktop the fewer resources your Mac will use in general.
If you have a cluttered Desktop, cleaning it up manually will likely end up at the bottom of your to-do list. That’s why you need to automate the process with Spotless.
Spotless is a decluttering app that lets you define specific rules for how you want different types of files to be managed. For example, you might want to put all images into the Pictures folder. After you create the rules, all you have to do is select all files on the Desktop and drop them into the Spotless icon in the menu bar, where it will deal with them in seconds.
Remove old iOS backups
You might not realize this but it’s easy to accumulate more iOS backups than you need. And they could take gigabytes of extra space for no reason.
To delete extra backups on Mac:
- Go to System Settings ➙ General ➙ Storage
- Click the information icon next to iOS Files
- Select any backups you don’t need
If you want more control over everything that happens between your iPhone and Mac, you need AnyTrans for iOS.
AnyTrans for iOS is the ultimate iPhone manager, letting you specify backups, transfer data, migrate between devices, convert photos, set ringtones, update apps, and more. All in an easy-to-use interface.
As you can see, having the startup disk full on Mac is not that critical. If you follow the steps outlined above, you’ll free up space and get rid of that warning in no time.
Best of all, the apps we mentioned, such as AnyTrans for iOS, Gemini, CleanMyMac X, Spotless, and Get Backup Pro, are there to help you and are available to you for free for seven days with the trial of Setapp.
Setapp is a platform of more than 240 curated Mac and iOS apps designed to solve any problem you can think of. Explore the collection at no cost today and see what you’ve been missing.
How do I restore my Mac without a startup disk?
You can’t restore your Mac without a startup disk, since it contains all the system files required for your Mac to function properly.
How to hide “your disk is almost full” notification on Mac?
To hide the disk full Mac notification, free up space by following the checklist above.
Why does my Mac keep saying startup disk is full?
When your startup disk is full, there’s no more space left on your Mac for its system operations. Delete files and apps you don’t need to resolve the issue.