1. Download Macos Catalina Offline Installer
2. Download Os Catalina Installer Usb

Most of the time, you can re-download the current version of macOS via the Mac App Store, and older ones via these links:

First, download the macOS Catalina Patcher from dosdude1.com. Open the Catalina Patcher app. Click Download a Copy. The macOS Catalina download should then begin. This might take a while, because Catalina is quite large – around 8GB. Plug in a USB memory stick. Click Create a Bootable Installer and wait for the installer to be.

1. This will download macOS Catalina into your Applications folder. Once completed, the installer will open, and you can follow the onscreen instructions to install macOS Catalina on your Mac.
2. Download and install. After you've completed your preparations, you're ready to download and install Catalina. Head to the Mac App Store, and in the left sidebar tap Updates.

However, I’ve run into a situation several times where the Software Update mechanism simply refuses to initiate a download:

Download Macos Catalina Offline Installer

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:

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:

softwareupdate --fetch-full-installer --full-installer-version 10.13.6

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.

Download Os Catalina Installer Usb

Update: Don’t miss this documentation from JAMF for more on the subject.