Mac OS Startup Disc Full Error: What is It?

Mac OS Startup Disc Full Error: What is It?

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I can bet that every Mac user has or will meet a full startup disk. Well, this issue have many solutions and I'm gonna tell you about them in this article. Today, we'll learn:

  • What's is Mac's startup disk full?
  • How to find the cause for it?
  • How can this problem be fixed?
  • How can it be prevented in the future?

If you are in a hurry and haven’t much time to read all that points, just skip the article to the 3-d section where we will teach you how to fix the problem of Mac startup disk full error.

Or, I can offer even faster and better automatic solution for the issue. Check the CleanMyMac X utility. It can help you saving gigabytes of space and you’ll never face the startup disk full issue. You can download it here for free.

NB: if you use macOS Sierra or macOS High Sierra, there is an Optimized Storage option that can solve the issue of the full HDD. It moves your files into the cloud storage. So, Sierra will message you when the disk gets full.


Click on Apple sign in the left top corner then choose 'About This Mac', you will see all information about you Mac, click on 'Storage' tab at the top of the window and you will see information about your storage.

Click ‘Manage’  button, the ‘Optimized Storage’ will open. However, usually it deals just with useless junk files and sends them to the storage making your personal files merging with junk. That’s why I recommend installing the CleanMyMac app to remove such files for sure, but not to move them to iCloud.

So, after I’ve said all that, let’s look deeper at the ‘startup full disk’ problem and what it actually means.

What's is Mac's Startup Disk Full Message Mean?

Let’s start with what is the startup disk in general. It is a partition or a whole disk that contains an active usable operating system (your macOS).

So, your hard drive includes disks or partitions. Each of them has some Mac data on it: operating system, apps, and so on. Mostly there is just one disk on Macs, but experienced users prefer to have several disks (2 or more).

Here is an imaginary example of one disk Mac:

  • a HDD is 500Gb.
  • all 500Gb storage is situated on one disk.
  • the OS and apps are situated on this one disk.
  • your only disk (it is your startup disk) is 500Gb.

With Mac that has two disks, that space is divided into parts. One part includes the OS (it is the startup disk) and the other one storages files and applications.

Of course, there can be several startup disks as well, but usually users prefer to have just one startup disk.

Why does Mac startup disk became full?

It can be explained easily. Can you imagine a fridge full of food with no more free space in it? So, your startup disk can be the same full either, but it’s not a nice news for any Mac user. It’s recommended using not more that 85% of the overall disk capacity (especially if we talk about a startup one). Errors can appear and its work will be much slower. So, if your macOS messages you about such a problem, don’t hesitate and hurry up to fix it!

What should you do now?

Remember our virtual packed fridge? Do the same! Get some free space! To clear space on your Macs startup disk you need to:

  • Delete unnecessary files from the disk.
  • Move some files to iCloud or an external HDD.
  • Add another internal HDD to your Mac.

After we have learned what is a startup disk, let’s go further and see what exactly can cause the lack of space on it.

How to Find the Cause for it?

Long story short, look under-the-hood of your Mac! :)

Firstly, we should find what is taking the space on your startup disk:

  • Open ‘Finder’ in the Dock.
  • Tap ‘Finder’ in the menu at the screen top.
  • Go to ‘Preferences’.
  • Click the checkbox called ‘Hard disks’ in the appeared window.


After doing that a hard disk's icon should appear on your desktop. This is how it looks:


These are your startup disks as they have an OS on them. If a few icons appear on the desktop, it means that you have several disks on your Mac. If you have just one icon appeared, you can skip this article to the moment called ‘What have taken up the startup disk space?’

If there are multiple disks, do the following:

Click ‘Applications’ on the Dock. Go to ‘System Preferences’ and click ‘Startup Disk’.

You’ll see something named ‘HD’ or ‘MainSSD’ there. It will also show you the number of an OS installed on your Mac.

As for me, I have just one system, here it is:

But if you are still not sure what disk is the startup one, do the next things:

  • Click the ‘Apple’ icon at the top-left.
  • Go to ‘About This Mac’.
  • Find a version number under the OS X name:

My version fully matches with one noted in the Startup Disk section. I can bet yours matches too.

What have taken up the startup disk space?

After we’ve made sure which disk is the startup one, let’s find out that ‘space stealer’.

Click ‘Apple’ at the left top of the screen.

Visit ‘About this Mac’.

Go to ‘Storage’. If you have an older version of OS X, you may go to ‘More info’ first, and then to ‘Storage’.

Here is my HDD:

I have 250Gb taken, and 46.76 Gb free. Find out how much free space does your disk have. It’s important for further ‘free space’ planning and for keeping in mind your probable disk capacity. So, you’ll be able to fix such problems easily after getting that knowledge.

How can this Problem be Bixed? Top-10 Ways of Doing it!

Check out these 10 ways of clearing space on your startup disk and choose the one that fits you the most!

1. Remove all cache from your Mac.

In some way, cache helps to run programs smoothly and in general, they work like kind of blueprints for a horse. However, after some time passes, cache accumulates and takes too much free disk space. This problem can be solved by removing it from time to time. Don’t worry, it won’t damage your Mac as it will create fresh cache files for your after rebooting it.

To clear the cache do the following steps:

  1. Open ‘Finder’ and select ‘Go’.
  2. Tap ‘Go to Folder…’
  3. Type: ~/Library/Caches, then delete bulky folders.
  4. Tap ‘Go to Folder’ again.
  5. Type: /Library/Caches (yes, it’s practically the same, but without the ~ symbol. Delete all bulky folders again.

Deleting the cache files is not harmful for your Mac, but still, I don’t recommend removing all of them, but just the most weighty ones.

You can check the folder: /System/Library/Caches too, but it’s not advisable if you don’t know about its contents. Anyway, the CleanMyMac app can easily help you to identify what can be removed safely, and what’s not. The cache may be cleared in just a couple of clicks!

Finally, after you’ve done all the steps, restart your Mac and enjoy the faster work.

2. Remove localization files (language packs)

Lots of applications are installed with other languages that are usually not necessary for an average user. To remove them you need to: 

After that, go to Contents > Resources and search all files that end with .lproj. These will be the language files and you can remove those that you don’t need and don’t know at all.

The CleamMyMac 3 app can be an alternative to passing through all those boring steps, it can remove all unnecessary localization files in a one click.

3. Get rid of iTunes Library backups

The latest iTunes versions create backups in the Library after every app update (as for me, those are nearly daily updates :) You don’t need them at all, so better move them to Trash.

  • Go to ‘Finder’.
  • Click ‘Go’.
  • Proceed with ‘Go to Folder’.
  • Go to ~/Music/iTunes/Previous iTunes Libraries.

Delete the old ones.

4. Delete old backups of the iOS

Such things as iOS backups usually take a plenty of space. You can remove them by doing the following:

  • Launch ‘Finder’.
  • Click ‘Go’.
  • Proceed with ‘Go to Folder’.
  • Go to ~/Library/Application Support/MobileSync/Backup.

Remove outdated backups and free more space!

5. Get rid of the software updates

Some unnecessary data for you devices is kept on disks. That’s how it can be removed:

  • Launch ‘Finder’.
  • Click ‘Go’.
  • Proceed with ‘Go to Folder’.
  • Go to ~/Library/iTunes/iPad Software Updates (or ~/Library/iTunes/iPhone Software Updates for your iPhone).

Keep in mind that you hardly even need those old updates, so don’t hesitate to remove them to Trash.

6. Delete unnecessary apps

This option is under appreciated. Removing unused outdated apps you don’t need any more will certainly save you some free space on a startup disk. However, make sure you do that correctly, but not by moving an icon to Trash. Leftovers can still take space on the hard drive disk.

That’s why I recommend you using CleanMyMac X again. This utility won’t leave any junk files after deleting apps and will save you tons of free time!

7. Clean the photo library

Usually, photos tale to-o-ons of space. First of all remove all copies, mistakenly taken pictures, low-quality ones and everything you don’t need.

After that, you can remove files created by the system. They are cache files in Mac Photos and service copies in iPhoto. But they are not necessary at all, so you can remove them.

How to remove the Photos cache:

  • Launch ‘Finder’ and find the ‘Photos’ library (it’s situated in ‘Pictures’ usually).
  • Ctrl & click the library and tap ‘Show Package Contents’.
  • Go to ‘Resources’ > ‘Modelresource’.

More folders should appear, and all of them contain cache. The problem is that you don’t know which files are safe to remove, and which are not. Nevertheless, CleanMyMac X knows is for sure, that’s why I use it for doing that. All in all, it’s safer for my Mac.

If you are an iPhotos user, repeat the first two steps that I’ve described above. Check the ‘Original’, ‘Modified’, ‘Master’ and ‘Preview’ folders to see what photos have copies as iPhotos sometimes acts rather mysteriously.

Please keep in mind that doing that is only your responsibility, so I won’t be able to help if you accidentally delete some critical files. That’s why I use CleanMyMac X in such situations, it always knows which files should be left obligatory.

8. Check the 'Downloads', 'Music' and 'Movies' folders

You'll surely be surprised at how many junk files are stored there. Just organize these folders by cleaning files you don't know or don't need.

In music folder, delete duplicates and songs you don't like to listen anymore.

The most pain is the 'Movies' folder and it's not because of the mess there. As for me, I could never delete some certain films. Still, sometimes your Mac will need sacrifices, so you can archive such favorite movies.

Here is the instruction on archiving a file:

Every file becomes smaller after the process and had .zip or .tar dimension. Such 'memory shaving' is necessary if you don't want to delete something, but need more space anyway. Do the next things:

  • Ctrl & click the file you want to archive.
  • Click on 'Compress'.

9. Organize the Desktop

You may be surprised with the fact that the desktop has to be cleaned too. In fact, some people have so messy desktops that it's hardly possible to look at them. A clean accurate desktop looks nicer and it helps the Mac to work faster! Yes, it's true!

10. Delete everything from the Trash

I'm not joking now! Cleaning the Trash is essential, but many people just forget about it. Even I forget.

When you delete something from your Mac, it doesn't disappear, but moves to Trash. So, it still in the Trash and taking free space.

  • Ctrl & click the 'Trash' icon.
  • Tap 'Empty Trash' and click on it.

Done

How can it be Prevented in the Future?

Let's see how we can prevent the full startup disk problem at all.

Do you remember how Mac's free space can be checked? Do it once more and see how much space is free now:

  1. Tap the 'Apple' icon at the top left of your screen.
  2. Go to 'About This Mac'.
  3. Choose 'Storage' (or 'More info' > 'Storage' for the older OS X versions).

You can see how much space you've cleaned.

I recommend cleaning your Mac every two-three weeks.

As for me, I use CleamMyMac 3 for that, it's easy, fast and efficient. I like that it lets me to clean all the junk files with a one click. So, I'll tell you about this app more. It really helps to prevent full startup disk.

The program scans your Mac for gigabytes of junk and deletes them, saving you much time that you'd spend by doing all that steps manually. Old backups, music duplicates, photo copies, outdated cache, and other things are taken into the app's work. I can affirm that it's not just a situational solution of the full startup disk issue, but a long-term problem solver.

I hope, my article was helpful in solving your full startup disk problem. Please share it with your friends, maybe they will be in need someday too. And don't forget to subscribe to our email list! There will be more Mac guides soon!