Download the macOS Catalina Installer and create a DMG file

macOS Catalina Download and convert to DMG

As usual with the last macOS backups, macOS Catalina also has no way of finding the macOS 10.15 installer as a public (and legal) download on the Internet. If you start the update on the Mac, the installer is loaded, but the Mac starts it directly. Once you have finished the installation, the installer is deleted from the Mac and you have virtually no file with which you can install Catalina on another Mac without having to load it again from the network.

There is no public download of macOS Catalina. I'll show you how to get the macOS 10.15 installer anyway.
There is no public download of macOS Catalina. I'll show you how to get the macOS 10.15 installer anyway.

In this article I would like to show you how to get the installer anyway and how to create a DMG from this file with the on-board tools of macOS.

Important: Do not download the update from the App Store

I just got the information from a friend that if you start the download in the App Store you only get a 19 MB file, which then does the actual installation and loads the installer. I don't know how to get to the large installation file of macOS Catalina this way. For this reason, I would recommend going through “System Preferences > Software Update”. If you still want to go via the App Store, you will find it MacOS Catalina installer here.

MacOS Catalina is also available in the App Store, but you shouldn't choose this way if you want to save the installer.
MacOS Catalina is also available in the App Store, but you shouldn't choose this way if you want to save the installer.

Exit macOS Catalina Installer and save the app

The first step we have to take is to start the installation process from “System Settings > Software Update”. After pressing the "Update" button, the Mac will start downloading the installation file from the web.

When the download is complete and the first window of the installer opens, we use the mouse to go to the menu item “Install macOS Catalina” in the top left and select the bottom entry “End macOS installation”.

To the right of the apple menu you come to the menu item via which the installer can be canceled before changes are made to the system.
To the right of the apple menu is the menu item that allows you to cancel the installer before making changes to the system.

Now we go to the “Applications” folder and look for the “Install macOS Catalina” file there. The file extension “.app” can also be seen in my screenshot (below), because I have the file extensions displayed. How to do that, you can read here.

Generate DMG with hard disk utility

Now the installer is secured. The next step now is to package this app in a DMG so that it is actually a file, because an ".app" file is usually only shown as a single file and is in fact a folder with all the contents, belonging to the app.

You can find out quickly by throwing the “macOS Catalina Installer” into Dropbox, for example. What arrives there only has a few kB and can no longer be used as an installer. But this is another story…

We definitely want to package the installer app in a DMG for easier use and shipping in the future. But you can save yourself the step if you copy the directly to a USB stick or an external hard drive.

We copy the installer from the programs folder into a new directory that we created on the desktop.
We copy the installer from the programs folder into a new directory that we created on the desktop.

Instructions: Create DMG image from folder

To do this, we create a new folder on the desktop and drag the “macOS Catalina Installer” into it. If you want to leave a copy in the Applications folder, hold down the ALT key during the drag-and-drop process. I named the folder macOS Catalina Installer 10-15, but you can be creative here. I would only do without periods and special characters in the file name so that there are no problems on other operating or file systems.

Next, open that Disk Utility and choose “File > New Image > Image from Folder” in the upper left corner. Here you will be asked for the folder from which the DMG is created. At this point we select our new directory on the desktop where the Catalina installer is located.

Now the hard disk service program only needs a few minutes to create the DMG and our handy macOS Catalina installer is ready, which can also be shipped via Dropbox or other services.

The DMG is ready, with which you can archive the macOS Catalina installer and use it for other Macs.
The DMG is ready, with which you can archive the macOS Catalina installer and use it for other Macs.

Create a bootable USB stick for macOS Catalina

At this point I would like to refer to the app”Install Disk Creator” link, which you can use to create a bootable USB stick for emergencies from the installer. If you are looking for a suitable USB stick with a USB-C and USB-A connector, you can look no further look at the 32GB stick from Eivotor.

However, things are much faster and more convenient with a small, external SSD. From my point of view, the good & cheap solution in this area is the Adata SD700, which is equipped with 256 GB of memory. I once had that ADATA SD600Q in the test and it had a very good data throughput at a good price.


My tips & tricks about technology & Apple

Did you like the article and did the instructions on the blog help you? Then I would be happy if you the blog via a Steady Membership would support.

66 Responses to “Download macOS Catalina Installer and create DMG file”

  1. How do I get the macOS Catalina Installer, I already have Catalina installed. Would like to erase the hard drive and put it back on again by hand, with Mojave and Catalina.

    Under Catalina, I can't update the update !!!

    Do I have to install Mojave or High Sierra first, then Mojave and copy and save the installer from there ???

    I tried yesterday until nothing worked, no mouse, no keyboard, at some point by chance I managed to install my backup, but I don't know how! ??? is normal there .... why is there no protocol where you can undo steps ????

    But otherwise, great site and good tips, just too stupid that I'm always on the tube ... crap. ;O)

    1. Hi Andreas! What speaks against restarting with the CMD + R key pressed? Then you come into a mode in which you can reinstall macOS Catalina on a different hard drive. Otherwise you can also use macOS Catalina as an installer Download from Apple using this link. I just tried it again. It worked.

  2. Hello
    Can someone help me I'm new with the IMac on the go
    2018 with Catalina
    It started with Ssl errors when sending mails
    No Safari, no mails, no update possible
    Lan is there
    Everything still works via Paralles Desktop
    A virus protection program loaded from the app store found something, but without success
    I created a backup via time machine
    I would be very grateful for any starting point

    1. Hello Thomas! The SSL errors in Apple Mail can, for example, be caused by the misconfiguration of the mail account. What does "no safari" mean? Do you mean Safari has no internet connection? Backup is good. I would try restarting the iMac and then holding down CMD + R. Then you come into the recovery and can install Catalina over it again. Try that and then log in again. And it's better to restart once too much than once too little. :D

  3. Moin Jens, great blog and helpful tips. However, I have a small problem: I can no longer find a download for the 10.15 operating system. as an installation. The new Big Sur is no longer supported by my hardware in mid-2012 Mac Book Air. I've been looking for a way to upgrade the High Sierra for days now. Do you have a tip? No version can be found in the app store.

    1. Hello mead! Give me a couple of hours. I'm putting all the macOS installers I have into my Dropbox right now. But unfortunately my village internet is a bit slow and there are quite a few gigabytes. : D

        1. Hello mead! I think you can only do that with Safari. A reader tried to load it with Firefox and got an error. Then it worked with Safari. Will you try again Which OS do you need?

  4. Hello, I want to go back to Catalina with mac Book Air from Mac OS Big SUR. Unfortunately I don't have a backup.
    Is there an easy way to do this?
    With kind regards,

    1. Hello Bert! So unfortunately not “easy”. That's a lot of manual work: install Catalina somewhere on a fresh hard drive and then copy the data over by hand. :(

      1. The data is not important to me, can I just download Catalina from the App Store and then install it? How do I have to proceed then?
        Thanks for the quick help

        1. Hello Bert! Yes, go then. I think so:
          - Restart and hold down (Shift) + (cmd) + (alt) + (r)
          - then delete the internal hard drive with the hard disk utility (APFS)
          – and now back out of the program and select “Reinstall macOS”.
          - I hope then he chooses Catalina

          If not, you'll have to install the system he suggests first and then upgrade to Catalina later.

    1. Hello Rudi! I currently have the problem that my Catalina Installer is in OneDrive and every download stops. I'll try a different browser now ... maybe it'll work. : D

  5. Hallo,

    was so far satisfied with High Sierra, but since updates have been discontinued, system work is due again. I don't like automatic updates at all and I used to always have an additional start hard disk on the go.

    Is APFS Beneficial? You should be able to install several systems in parallel on an external SSD. Do partitions still make sense, e.g. to have a place for work files in addition to a start volume on an external SSD?

    A Catalina DMG would be very helpful to me.

    1. Hello Ruben! Yes, APFS is definitely an advantage. If only because you don't need partitions, you can create "volumes" that then have a dynamic size. They grow and shrink in size. depending on the memory requirement. This is how you get the most out of the SSD. Because of Catalina… “You have mail!”. ;-)

  6. Hi Jens,
    I have an iMac in mid-2011 and am very satisfied with High Sierra, but now my Citrix workspace app requires at least operating system 10.15.

    My plan: I install the Catalina 16 in my Parallels Desktop 10.15 and then download the new version of the Citrix Workspace app - shouldn't it work that way?

    Now of course I'm looking for a download for Catalina and can't find anything.
    May I also ask for “mail”?

    1. Hello Alex! Yes, the plan should work like this, although I don't know the app. But with Parallels Desktop it should work. “Mail” is coming soon. :D

  7. hey jens,
    I also have the problem of not being able to update to Catalina on the Macbook air 2012. I would be very happy if you post with the link!
    Thank you very much!!!

  8. Hi Jens, could I ask you for the link by post too? That would be great. I just want from Mojave to Catalina. Mittkerwile is only offered in Big Sur.

  9. Hello, Jens! I just landed here looking for salvation. I have 2 Macs from 2012, in which I install an SSD and then want to install Catalina 10.15 using a USB stick, but it also doesn't work for me to download 10.15 (only this 19,1MB file comes from here ...).

    So I also ask you: Could you send me the “rescue link”?

    Best regards

  10. Hello Jens, wonderful, thank you very much! I've already looked, looks very promising! I will register soon!
    Best regards

  11. Hi Jens,

    Please excuse my confusing presentation of the message.
    Here again in correct rendering:

    The "macOS Catalina.dmg" folder image is created ...

    Process with status 1 failed: The process is not permitted

    Action failed ...



    1. Hello Werner! It's hard to say what it depends on. The error message sounds like he has a problem with the disk. Can you try to create the image on another hard drive? Otherwise I don't know where it could get stuck.

  12. Hello, Jens!

    I have a MacBook Air 2017 and cannot install Big Sur because I still have software that is incompatible with it.

    Could you also send me the link for Catalina? This works fine on my other devices.

    Thank you!

      1. Hello Stefan! Yes this is not a problem. You can upgrade to Catalina from any system using the installer. I just can't pass it on because it's not open source. But I can do it for you official download links in the forum . Recommend
        And if you want to install it on an external hard drive, you can also clone your current system (Carbon Copy Cloner or SuperDuper will do the job) and then just upgrade the system on the external hard drive and leave the old one as it is. Then you have both and do not need a “stand-alone installer”.

  13. Hallo,
    I'm also desperately looking for Catalina and BigSur. I also registered in the forum because at some point there will be talk of a cloud or FTP. I also saw this list with the Apple versions, but unfortunately all links are only linked to the Apple Store and error messages appear. Version too old. other version required etc ...
    The BigSur is supposed to run more stable than Catalina and have a better performance ..
    I have this MacBookPro MacBookPro9,2. Can the operating system be installed on this without a patch? When I try to load via the store, an error message appears and it stops. #
    Many thanks for your help. Have already secured HighSierra, Mojave, only with Catalina and BigSur I can't find the links anywhere :(

  14. Hello, yes I also read that only Catalina is supported. However, I also saw various YouTube instructions on how to install Big Sur on older Macs. I've read his forum from you guys you would recommend Bigsur. Allegedly runs better, faster than Catalina.
    But back to the downloads again, maybe I'm just too stupid but with Safari when I open your links I land back on the Apple AppStore page then click on download and then the download runs under system settings / software update and then stops or starts ( BigSur) not even at all.

    1. Hello, tobias! Yes, there is a possibility, but I have no experience with it. I only install on Macs, which is officially possible. If the download links just don't want you, then I would give you the app ANYmacos recommend. It offers the download of different macOS versions and you can optionally create a boot stick with it. Otherwise, I'd still say Big Sur is doing better than Catalina. There were far fewer reader complaints about Big Sur than about Catalina. : D

  15. Does anyone have older versions of Mac OS X? I'm looking for 10.4.11 (Tiger) for my old Powerbook G4 (only an original CD from 10.1.1 is included).

  16. What I don't understand: why does the have to be enchanted into a dmg first? I can also copy it to a Sick or something similar.
    Or not?

    1. It says in the article: “Now the next step is to package this app in a DMG so that it is actually a file, because an “.app” file usually just shows up as a single file and is actually a folder with all the content that goes with the app.”
      But yes, if you use a USB stick for distribution, you can also drag the installer directly onto it. I did it via Dropbox and everything falls apart because only a 0 KB file arrives at Dropbox. Because it's not a single file, it's an app directory. And that doesn't arrive at Dropbox in its "original" state.

  17. Hello, Jens!
    Thanks for the great guide!
    Do you have to do the last step with the bootable stick if you want to set up a Mac from scratch or is the DMG file enough for that?
    Thank you and best regards

    1. Hello Ingo! I've just looked at the instructions again, but I still don't quite understand which "last step" you mean that you might be able to omit. 😊

  18. Hello, Jens! Thank you for your quick response! Sorry that I made my request unclear. I want to set up my iMac from scratch and the recommended operating system is Catalina (iMac late 2012). Yosemite is on it so far. Can I install Catalina on a portable disc using the DMG file or is it mandatory to create a bootable stick with “Install Disc Creator” for it? Best regards

    1. Hi Ingo! I think (!) you need to create a bootable stick. Because otherwise the "volume" from which the installation is to take place would be gone after the restart. But to be honest I haven't tried it. You can just test it. Copy the DMG to the stick and start the installer. If it doesn't work, he'll just complain. Nothing will break here.

  19. Hello, Jens! Many thanks for the help! Yes, it must actually be a bootable stick. I hope I can fix this with Install Disc Creator! Best wishes to you and thanks again 1000!!

      1. Hello, Jens!
        Sorry to bother you again. I get the message from the app: “An error occurred. Try ejecting the destination disk an reinserting it, or rebooting. It couldn't be unmounted to erase it."
        I followed the instructions - unfortunately that didn't help. The error message remains - I tried it with two different removable media. Do you have any idea why? Many greetings

  20. Dear Jens! All right, that worked. Maybe I know where the error was. I downloaded the Catalina file to install on my iMac running Yosemite (it was only a few Mb in size). The terminal "complained about this file". I then tried the whole thing on my MacBook Pro, which is already running Catalina, and the Catalina file to install (which I downloaded again) was several GB this time - so it worked without any problems. I'm assuming that "Install Disc Creator" couldn't handle the file either, although the error message doesn't match. Now what that means for people who have the same problem but don't have a Mac with a higher OS handy I can't say. You'll probably have to update "gradually". I hope I can manage the rest now... Warm regards - Ingo

    1. Glad it worked out. 😊 You probably had the installer that still loads the whole 5 gigabytes. You can't create bootable media with it.

  21. I haven't read all the comments and it's not specifically about the Catalina update. However, at the top of the text there is a note not to load the macOS installer via the AppStore, since then you would not get the actual installer apps on the disk... (or should this really ONLY apply to Catalina, which surprises me would).

    The fact is that I was able to download the installers for Big Sur and Monterey from the AppStore under Mojave without any problems, then finished the actual installation by exiting the installer app, as Jens described, and then the two approx. 12 GB large installer apps in the Applications folder - for later use.

    As it is said, however, you should first save copies of the same elsewhere on the disk as a precaution, since the app files in the programs folder would be automatically deleted after installation. Whether that's true remains to be seen...

Post a comment

Your e-mail address will not be published. Required fields are marked with * marked

In the Sir Apfelot Blog you will find advice, instructions and reviews on Apple products such as the iPhone, iPad, Apple Watch, AirPods, iMac, Mac Pro, Mac Mini and Mac Studio.