(This command reserves an 8,900 MB virtual footprint formatted using Mac OS Extended Journaled layout). Step 2: Mount the Disk Container
Apple typically provides the full installer as an file in your Applications folder rather than a direct DMG. However, you can use these official tools to fetch it:
Write the installer installation media contents into your raw disk image via the embedded createinstallmedia utility tool:
Type your password and wait for the "Install media now available" message. How to Install macOS Catalina 10.15.7 Plug the bootable USB into the target Mac. Restart the Mac and immediately hold the Option (Alt) key . Select the Install macOS Catalina drive from the boot menu. Download Macos Catalina 10.15.7 Dmg File
The completed macOS_Catalina_10.15.7.dmg file will appear directly on your Desktop screen. How to Create a Bootable USB from the DMG
Apple distributes the OS package inside an application wrapper rather than a flat .dmg container. To build a portable disk image file for archiving, virtual machine deployments (like VMware or VirtualBox), or Windows deployment environments, you must convert the bundle via the command line.
I can provide the exact steps for whichever path you choose. (This command reserves an 8,900 MB virtual footprint
sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/install_build --nointeraction Use code with caution.
To provide the most relevant download link, are you using a Mac or a Windows PC to prepare the installer? How To Create A Bootable MacOS Catalina Install Drive
If you need the raw installation files immediately, use these trusted sources. For security, always download macOS files directly from Apple's servers or verified repositories to avoid malware. How to Install macOS Catalina 10
Downloading a often requires a few extra steps, as Apple primarily provides the installer as an application ( .app ) through the Mac App Store rather than a direct DMG link.
When asked to confirm that you want to erase the volume, type Y and press .