Most of the time, you can re-download the current version of macOS via the Mac App Store, and older ones via these links:
However, I’ve run into a situation several times where the Software Update mechanism simply refuses to initiate a download:
As facing huge issues on the new operating system, after the passage of time finally, all issues bugs fixed. All the expectations are full filled with fixing the errors, bugs. And what the users expected completed. If you remember when macOS Catalina released. There was doubt about the installation process, users were doubting on the security. Connect the macOS Catalina install drive to the target Mac. Hold down the OPTION key upon system boot, and continue holding Option until you see the Mac boot menu. Choose the macOS Catalina installer volume to boot from. The MacOS Catalina boot disk will allow you to install MacOS Catalina as an upgrade, and also to perform clean installations.
Thankfully, macOS installers can be downloaded via Terminal in macOS Catalina. This command will download the most recent version of macOS, depositing it in your Applications folder:
softwareupdate --fetch-full-installer
The softwareupdate command has some neat tricks up its sleeve, as pointed out by Armin Briegel:
Download Mac Os Catalina Installer
The --fetch-full-installer flag has a sub-flag: --full-installer-version which allows you to download a specific version.
During my testing in the Catalina beta version I was able to download 10.15, 10.14.6, 10.14.5, and 10.13.6. I was not able to test if 10.13.6 would download the hardware specific build of 10.13.6 for the 2018 MacBook Pro, since I do not have that hardware.
So, to pull 10.13.6 down, you’d use:
Mac Os Catalina Installer Stuck
softwareupdate --fetch-full-installer --full-installer-version 10.13.6
Mac Os Catalina Installer
I wish Apple would just have a support document up with direct downloads for all of this stuff, but this tool is not a bad alternative.
How To Download Mac Os Catalina Installer
Update: Don’t miss this documentation from JAMF for more on the subject.