"Your startup disk is almost full" means the disk your Mac starts up from, usually called Macintosh HD, has very little free space left. Nothing is broken. But macOS and your apps need room to save, download, update and copy, and when that room runs out, those tasks start to fail.
The fix has two parts. First, get a little space back quickly, so your Mac can work while you look: empty the Trash and restart. Then find the few large things that filled the disk, in System Settings › General › Storage, and remove or move the ones you don't need.
Two other messages usually mean the same thing. "The operation can't be completed because the disk is full" comes from Finder or an app when a copy or save runs out of room. "No space left on device" is the system's own wording for the same problem, and it shows up in apps and developer tools.
The one thing to check before you act on either: which disk is full. It isn't always your startup disk. It can be an external drive you're copying to, or a virtual disk inside an app such as Docker.
What "your startup disk is almost full" means
The warning is about space, not about the health of the disk. macOS shows it when the disk it runs from has little room left.
What is the startup disk?
The startup disk is the disk your Mac starts up from: the internal disk, unless you've set your Mac to start from an external drive. In Finder and in Storage settings it's usually named Macintosh HD, unless you renamed it.
Since macOS Catalina, that one disk holds two volumes: a read-only one for macOS itself and a data volume, Macintosh HD - Data, for your files and apps. They share one pool of space, so space used on either comes out of the same total.
When does macOS show the warning?
Apple doesn't publish the point at which the warning appears. Treat it as late notice, not an early warning: by the time you see it, the disk is already short of room.
Don't wait for it, either. A large download, a video export or a macOS update can need more room than you have left, so a disk can be "full" for one task well before macOS says anything.
Is a full startup disk bad for a Mac?
A full disk doesn't damage anything, but your Mac can't do much with it. Documents fail to save, downloads stop partway, copies fail, and updates won't download or install. Apple's own article on freeing up space opens with the same problem: not enough room to download, install or copy.
macOS also uses the startup disk as working space. When apps need more memory than your Mac has, macOS moves some of it to swap files on the startup disk. And Time Machine keeps its local snapshots only on disks with plenty of free space, so a nearly full disk goes without them.
Will freeing space make my Mac faster?
Freeing space fixes the failures a full disk causes. It isn't a way to make a Mac that's working normally any faster. Removing caches, in particular, can make apps a little slower for a while, because they rebuild what they lose.
The other messages that mean the disk is full
Different parts of macOS say "the disk is full" in different words. They lead to the same fix, but each one tells you something different about which disk to look at.
"The operation can't be completed because the disk is full"
Finder and many apps show this when a copy, a move, a download or a save needs more room than the disk has. The disk in question is the one being written to, which isn't always your startup disk.
If you were copying files to an external drive or a USB stick, that drive is the full one. Select it in the Finder sidebar and choose File › Get Info to see its available space. If you were saving or downloading to a folder on your Mac, it's the startup disk.
"No space left on device"
This is the system's standard wording for a write that found no free space on a disk. Programmers know it as ENOSPC, error 28. You'll see it in developer tools and in apps that show the system's message as it is.
Unlike Finder's message, it doesn't say which disk it means. The full device can be your startup disk, an external drive, a disk image or a virtual machine's disk.
"No space left on device" in Docker and virtual machines
Tools that run Linux on your Mac, such as Docker Desktop, keep their own virtual disk inside a single file. That disk has a maximum size, set in Docker Desktop's Settings › Resources › Advanced. When it's reached, builds and containers inside Docker run out of room, even if your Mac has plenty.
The fix then is inside the tool. In Docker Desktop, remove images and containers you no longer need in the Dashboard. Never delete the disk image file in Finder: it holds every image, container and volume, and Docker's documentation also warns against moving it there.
"Not enough space" for a macOS update
When an update won't download or install, the startup disk is the one that's short. An update needs room both for its download and to install, and it needs truly free space, not space macOS only promises to free.
Apple says Software Update can use less storage to download and install updates than other ways of getting macOS, so use it rather than a full installer when space is tight.
| Message | Where you see it | Which disk is full | Check first |
|---|---|---|---|
| Your startup disk is almost full | A macOS alert | The disk your Mac starts from | Storage settings |
| The operation can't be completed because the disk is full | Finder or an app, while copying or saving | The disk being written to | Get Info on that disk |
| No space left on device | Apps, developer tools, installers | Any disk, including a virtual one | Which tool reported it |
| An update won't download or install | Software Update | The startup disk | Free space in Disk Utility |
First aid: get a little space back right now
When the disk is completely full, even looking for what filled it can be hard. Apps may stall, and Storage settings may be slow to finish counting. Start with the steps that free space without any decisions, then look properly.
Empty the Trash
Moving something to the Trash doesn't free its space. It stays on the disk until you empty the Trash, so you can put it back. On a full Mac, the Trash can be holding gigabytes you thought were gone.
Click the Trash in the Dock and look through it first, because emptying it is permanent. Then click Empty at the top right of the window, or choose Finder › Empty Trash, and confirm.
To remove one large item and keep the rest for now, Control-click it in the Trash and choose Delete Immediately. That's also permanent, so use it only on things you're sure about.
Check the other places deleted items wait
Some apps keep deleted items for a while before they let the space go. Photos and Messages keep them in Recently Deleted for up to 30 days. In Mail, choose Mailbox › Erase Deleted Items and Mailbox › Erase Junk Mail to clear what's waiting there.
Each external drive has its own hidden Trash. Items deleted from a drive keep their space until you empty the Trash while that drive is connected.
Restart your Mac
Restarting clears macOS's swap files, which can take several gigabytes when apps have used a lot of memory. Save your work and quit the apps you have open first, so nothing unsaved is lost.
Restarting is a one-off gain. Swap grows again as you use memory-hungry apps, and that's normal.
Start up in safe mode if you need more room
Apple suggests safe mode when you need temporary space for a task, such as installing a macOS update. In safe mode, your Mac clears some system caches, including font caches and the kernel cache, which macOS creates again as needed.
On a Mac with Apple silicon:
- Choose Apple menu › Shut Down, and wait until the screen is black.
- Press and hold the power button until Loading startup options appears.
- Select your startup disk.
- Press and hold Shift, then click Continue in Safe Mode.
- Log in. You may need to log in twice, and you may see Safe Boot in the menu bar.
On an Intel-based Mac, turn it on or restart it, then immediately press and hold Shift until the login window appears. To leave safe mode, restart normally.
What each quick fix gives back
| Quick fix | What it frees | How long it lasts | What it costs |
|---|---|---|---|
| Empty the Trash | Everything you've deleted | For good | Items can't be put back |
| Erase deleted mail and Recently Deleted | Deleted messages and photos | For good | They can't be recovered |
| Restart | Swap files | Until memory fills again | Nothing |
| Safe mode | Some system caches | Until macOS rebuilds them | A restart, twice |
Find out what's filling your startup disk
With a little room back, look before you remove anything else. On most Macs, a handful of things take most of the space, and they're different on every Mac.
Open Storage settings
In macOS 27 Golden Gate, choose Apple menu › System Settings, click General in the sidebar, then click Storage. macOS Tahoe 26 works the same way, as do Sonoma, Sequoia and Ventura. Before Ventura, choose Apple menu › About This Mac, then click Storage.
The bar at the top shows used and available space, split by category. Give it a minute: Storage settings works out its figures in the background, and they move while it counts. To see every volume and the free space on each, click All Volumes.
Read the categories, largest first
Below the bar, each category shows its size. Categories with an Info button let you act: click it to see the largest items, then select one and click Delete, or click Show in Finder to look at it first. Apple singles out Applications, Documents, Messages, Music Creation, Podcasts, Trash and TV.
| Category | What it usually holds | Where to start |
|---|---|---|
| Documents | Files in your home folder, including Downloads | Sort by size or last accessed |
| iOS Files | iPhone and iPad backups and software files | Old backups and update files |
| Messages | Conversations and their attachments | Large attachments |
| Applications | Apps you installed | Apps you no longer use |
| Photos | Your System Photo Library | Optimize or move the library |
| System Data | Caches, logs, swap, snapshots and anything uncategorized | Finder, or the apps that made it |
The macOS and System Data categories have no Info button, and you can't remove anything from them in Storage settings. Apple says macOS manages System Data's contents; for your own data in it, use Finder or the app that created it.
Why Finder and Storage settings disagree
Apple draws a line between two numbers. Free space is open space on the disk. Available space is free space plus purgeable space: caches, local snapshots and iCloud downloads that macOS has agreed to remove when something needs the room.
Finder shows available space, so it can say you have room when a large copy still fails. To see the free figure, open Disk Utility, select your startup disk's volume, and click the Info button in the toolbar. The guide to why storage numbers differ goes through every reason.
Where the space usually goes
Most full Macs are full for a few predictable reasons. Here are the usual suspects, with the range they reach on Macs that have them at all.
- Trash0–100 GB · Review first
- Downloads and large old files5–100 GB · Review first
- iPhone and iPad backups10–200 GB · Review first
- Messages attachments5–100 GB · Review first
- App caches2–30 GB · Safe
- Per-user temporary files1–70 GB · Managed by macOS
- Swap and sleep image1–20 GB · Managed by macOS
Typical ranges from the research behind the app's catalog, on Macs that have each item. Many Macs have far less of each, and none of these are fixed sizes.
Free space for good: what to remove first
The quick fixes buy time. Lasting room comes from the large things you no longer need. Work through them in this order, which starts with what costs least to lose.
Downloads and installers
The Downloads folder is the easiest place to win back space, because nothing else depends on it. Open it from the Dock, or choose Go › Downloads in Finder. Choose View › as List and click the Size column to put the largest files first.
Disk images and installer packages, the .dmg and .pkg files, are rarely needed once an app is installed: it runs from Applications. Archives you've already opened, such as .zip files, often sit next to the extracted copy. Check the copy is there before you remove the archive.
An old macOS installer is worth looking for too. An app such as Install macOS Tahoe in Applications takes many gigabytes, and you only need it to install that version again. Apple lets you download installers again for the versions your Mac supports.
Large files you've finished with
In Storage settings, click the Info button next to Documents, then sort by Size or Last Accessed. A file of several gigabytes you haven't opened in a year is a good candidate: an old screen recording, an exported video, a disk image from a finished project.
Before you remove one, ask whether it's your only copy. If it might be, copy it to an external drive, open the copy to check it works, then remove the original.
iPhone and iPad backups
Each device you back up to this Mac keeps a backup that can take tens of gigabytes, and backups of devices you've sold stay until you delete them. Click the Info button next to iOS Files in Storage settings, select an old backup, and click Delete.
A backup may be the only copy of what's in it. Check the device backs up to iCloud first. The same list shows iPhone and iPad software files, which are safe to remove: Finder downloads the current version again when it needs one.
Messages, Mail and media
Messages keeps every photo, video and file from your conversations. Click the Info button next to Messages in Storage settings to see the largest attachments, or delete them in Messages itself. With Messages in iCloud, deleting on your Mac deletes on your other devices too.
Music, TV shows, movies and podcasts you can stream or download again are safe to remove from the Mac. Apple suggests starting with those. Songs you imported yourself may exist only on this Mac, so keep a copy of them.
Apps you don't use
Click the Info button next to Applications to see apps by size. Quit an app before you remove it. If it came with its own uninstaller, use that; otherwise drag the app to the Trash, then empty the Trash when you're sure.
Removing an app leaves its caches and data folders behind. Most are small, but some apps leave gigabytes, and some of it can be your own work.
Caches
Apps keep caches in ~/ so they can load things faster, and Apple's guidelines say an app should keep only data there that it can create again. Remove a cache and the app rebuilds it, more slowly at first.
To clear one, quit the app, then in Finder choose Go › Go to Folder, enter that path, and move the app's folder to the Trash. Never move the Caches folder itself. The catalog's entry on app caches explains what to expect.
Other people's accounts
If other people have accounts on this Mac, their files count against the same disk, under Other Users in Storage settings. Apple suggests deleting accounts that no longer need access, or asking their owners to free space from their own accounts.
Apple also suggests checking the Users folder on Macintosh HD for data left by deleted accounts. An account deleted with Save the home folder in a disk image leaves that image in a Deleted Users folder there, and one deleted with Don't change the home folder leaves the whole folder in Users.
When deleting doesn't free any space
Sometimes you remove a large file and the available space hardly moves. There's always a reason, and it's rarely a fault.
Is the file still in the Trash?
It almost always is. Space comes back only when the Trash is emptied, and items deleted from an external drive keep their space until you empty the Trash with that drive connected.
Is a Time Machine snapshot holding it?
If you back up with Time Machine, your Mac keeps local snapshots: one about every hour, each kept for 24 hours, plus one of your last successful backup and one before each macOS update. A snapshot holds on to files you've deleted since it was taken.
Apple says snapshots don't take the space needed for downloads, copies or new software, and that Time Machine removes them as they age or when space is needed. If you need the room now, the guide to Time Machine local snapshots shows how to remove them in System Settings or Disk Utility.
Was it an iCloud Drive file?
With Optimize Mac Storage on, iCloud Drive keeps only some files downloaded. Deleting an iCloud Drive file deletes it from iCloud and from your other devices, which is rarely what you want when you're only short of space here.
To free space and keep the file, Control-click it in Finder and choose Remove Download. It stays in iCloud and shows a cloud icon on this Mac, and downloads again when you open it.
Was it a copy that shared its space?
On Apple's file system, copying a file on the same disk can make a clone that shares the original's space until one of them changes. Deleting one of two clones frees almost nothing, because the other still uses the space. That's normal, and it's why adding up file sizes can overstate what you'd get back.
Is the space purgeable rather than free?
Finder counts purgeable space as available, so a disk can show room it doesn't really have yet. macOS frees purgeable space when something asks for it, but not always as fast as a large task asks. The guide to purgeable space explains what's in it.
If your Mac is too full to start up or log in
This is rare, and Apple doesn't document a full disk as a cause of startup trouble. But if your Mac stalls at startup or at the login window after warning you about space for days, these are the steps Apple documents, in the order worth trying.
Try safe mode first
Safe mode clears some system caches, which may give a nearly full disk enough room to finish starting up. Use the steps earlier in this post. Once you're logged in, empty the Trash and remove a few large files you're sure about, then restart normally.
Check the disk with First Aid
If startup still doesn't finish, start up in macOS Recovery and run First Aid. On a Mac with Apple silicon, shut down, then press and hold the power button until the Options button appears. Click Options, then Continue, and enter an administrator password if asked.
In the Recovery app, select Disk Utility, then click Continue. Apple says to run First Aid on each volume, then each container, then the disk itself. When you check Macintosh HD, check Macintosh HD - Data too.
Copy files off with Share Disk
On a Mac with Apple silicon, macOS Recovery can share its disk with another Mac over a USB, USB-C or Thunderbolt cable. In the Recovery app, choose Utilities › Share Disk, select the volume and click Start Sharing.
On the other Mac, open a Finder window, click Network in the sidebar, double-click the shared Mac, click Connect As, choose Guest and click Connect. You can then copy the files you care about to safety. On an Intel-based Mac, target disk mode does a similar job.
Don't reinstall or erase to make room
Reinstalling macOS from Recovery keeps your personal files, Apple says, so it doesn't make room: your files are still there afterwards. Erasing the disk does make room, by removing everything. Neither is a fix for a full disk.
Which disk is full? Volumes, partitions and external drives
Knowing which disk ran out saves a lot of searching. Storage settings and Disk Utility both show it, if you know where to look.
Do volumes share space?
On Apple's file system, the volumes in one container share its free space. Macintosh HD and Macintosh HD - Data are in one container, and so is any other APFS volume you added to the internal disk. Any of them can use the free space, and filling one leaves less for all the others.
If you see more than one disk under All Volumes in Storage settings, your internal disk has several volumes or containers. Apple's page on shared APFS space explains how to read the graph.
What if the disk is partitioned?
A partition is different: its space is fixed and isn't shared. If you split your disk into partitions, the one macOS runs from can fill up while another still has room.
Apple notes that Storage settings' recommendations apply only to the partition that holds your home folder. Moving files to the other partition frees space on the full one, just as an external drive would.
What if it's an external drive?
When Finder says a copy to an external drive can't complete, that drive is full, not your Mac. Empty the Trash with the drive connected, because items deleted from it are still on it. Then remove or move what you don't need on that drive.
A Time Machine backup disk is a different case. Time Machine fills its disk by design and removes the oldest backups when it needs room, so a full backup disk is expected.
What not to do when the disk is full
A full disk makes drastic fixes look tempting. These are the ones that cause more trouble than they solve.
Don't paste Terminal commands from a web page
Guides that ask you to paste a command into Terminal to "free up space" are best closed. Commands that delete files can't be undone, and fake cleanup guides are a known way to install malware. Everything in this post works through Finder, System Settings and the apps themselves.
Don't delete folders you don't recognize
The folders that look biggest are often the ones to leave alone. Removing them can lose data, break apps or leave macOS repairing itself.
| Tempting fix | Why not | Instead |
|---|---|---|
| Delete the System folder or other macOS folders | macOS protects and manages them | Nothing: leave them to macOS |
| Move the whole Library or Caches folder to the Trash | Every app keeps its data and settings there | Remove single caches inside, with the app closed |
| Delete files inside the Photos library | It's a database that Photos manages | Optimize in Photos, or move the library |
| Delete iCloud Drive files to free space | Deleting removes them from every device | Use Remove Download |
| Delete swap files or the sleep image | macOS is using them | Restart |
| Delete Docker's disk image in Finder | It holds every image, container and volume | Clean up in Docker Desktop |
| Reinstall macOS | Your files stay, so the space doesn't come back | Find and remove what filled the disk |
Don't clear app preferences or saved state
App preferences and saved window state are tiny files. Removing them frees almost nothing and resets the apps. They aren't caches, whatever a cleanup guide says.
Don't trust alarming pop-ups
A web page or an app that says your Mac is "infected" or "full of junk" and offers a download isn't macOS. The real warning comes from macOS itself, and the fix doesn't need anything new installed.
Keep the warning from coming back
A disk that filled once tends to fill again in the same way. Caches, backups, attachments and downloads all grow without you saving anything.
Turn on the recommendations that suit you
Storage settings offers three recommendations. Each hands part of the job to macOS, and each has a cost worth reading first.
- Store in iCloud keeps your Desktop and Documents folders, photos and messages in iCloud, with only recent files and optimized photos on the Mac when space is needed. It uses your iCloud storage plan, and older files need a connection to open.
- Optimize Storage removes Apple TV movies and shows you've watched and keeps only recent mail attachments on the Mac when space is needed.
- Empty Trash automatically erases items that have been in the Trash for more than 30 days. After that, they're gone for good.
Let macOS clear what it can
When space is needed, macOS also clears caches and logs that are safe to delete, Apple says: temporary database files, interrupted downloads, staged macOS and app updates, Safari website data and more. You don't need to do anything for that, but it helps to know why free space sometimes rises on its own.
How much free space should you keep?
Apple doesn't publish a single figure, and rules of thumb such as "keep 10% free" aren't Apple's. A better rule: keep room for the largest thing you do. A macOS update, a big download or a video export each needs its space up front.
If you've removed what you can and you still run short, what's left is your own data. Then more storage is the answer: an external drive for archives, video and the Photos library, or a larger iCloud plan with Store in iCloud on.
The guide to freeing up space on a Mac covers every place space goes.
Look every month or two
A short check catches growth before it becomes a warning:
- Open Storage settings and note the three largest categories. One that has grown since last time is where to look.
- Look through the Trash, then empty it.
- Sort Downloads by size and clear what you've finished with.
- Delete backups of devices you no longer have.
- Remove apps you haven't opened in months.
How the app does it
Wombit is a native Mac app that shows what's using your storage, explains every item in plain language, and clears it safely: Trash first, undoable and logged. It scans the whole disk or any folder, reading only names, sizes and dates, and file names and paths never leave your Mac.
Its space meter, in the app and in the menu bar, shows the available space honestly, beside what's truly free. The menu bar item can also check whether a waiting macOS update fits before you start it.
The map is the home screen. Select anything to see what it is, how safe it is to remove and what removing it costs, with a Move to Trash or Clean Up button. Folders macOS didn't let it read are listed, not skipped, and hard links and APFS clones count once.
Items the catalog knows get one of four levels:
- Safe: the owner recreates it and nothing is lost, such as app caches. These start checked, and only they count in the headline number.
- Usually safe: it comes back at a cost, such as an old macOS installer.
- Review first: it may be the only copy, such as the Trash, iPhone backups, Messages attachments and large old files. You choose.
- Managed by macOS: local snapshots, swap and temporary files are explained and left to macOS's own mechanism, never moved.
The analyzer, the map, the explanations, the space meter, Undo, Put Back and Empty Trash are free. Cleanup, the Apple Data actions for backups, installers and large old files, What Changed and the alerts when space runs low are PRO: one payment of $4.99 with lifetime access.
Every Pro tool's review is free to open, and the alert that there isn't room for a macOS update always comes.
Frequently asked questions
How do I fix "your startup disk is almost full" on my Mac?
Empty the Trash and restart first, to get a little room back. Then open System Settings, click General, then Storage, and work down the largest categories: Downloads, old iPhone backups, Messages attachments, apps you don't use and large files you've finished with. Move files you want to keep to an external drive rather than deleting them.
Why does my Mac say the disk is full when Finder shows free space?
Finder shows available space, which includes purgeable space: caches, Time Machine's local snapshots and iCloud downloads that macOS will remove when something needs the room. A large copy or update can ask for space faster than macOS frees it. Disk Utility's Info button shows the free space on its own.
Can a full startup disk damage my Mac?
It doesn't damage anything, but your Mac can't work normally with it. Saves, downloads, copies and updates fail, and macOS has less room for the swap files it uses as extra memory. Freeing space fixes those failures.
What does "no space left on device" mean on a Mac?
It's the system's standard message for a write that found no free space on a disk. The disk can be your startup disk, an external drive, a disk image or a virtual disk inside a tool such as Docker Desktop. Check which app or tool reported it to find the disk that's full.
Why can't I copy files to my external drive even though my Mac has space?
When a copy fails with "the disk is full", the full disk is the destination, not your Mac. Select the drive in the Finder sidebar and choose File, then Get Info, to see its space. Items you deleted from the drive keep their space until you empty the Trash with the drive connected.
Does safe mode free up disk space on a Mac?
A little, and only for a while. Safe mode clears some system caches, such as font caches and the kernel cache, and macOS builds them again as needed. Apple suggests it when you need temporary room for a task such as a macOS update.
How much free space should I leave on my Mac's startup disk?
Apple doesn't publish a single figure, and rules such as keeping 10% free aren't Apple's. Keep enough room for the largest thing you do, such as a macOS update, a large download or a video export, because each needs its space before it starts.
Is it safe to delete System Data when the startup disk is full?
Not as a whole. System Data is a mix of caches, logs, swap files, snapshots and app data, and macOS manages much of it. App caches are safe to clear with the app closed; swap files and snapshots are left to macOS or removed through Time Machine's settings.