Solution: Error: Cask adoptopenjdk8 exists in multiple taps

I wrote how I solved the error in Homebrew, “Error: Cask adoptopenjdk8 exists in multiple taps”.


  • macOS Mojave Version 10.14


When I try to install Ruby 2.1.5 with RVM, the command brew cleanup is automatically executed and I got the following error messages. The command that I used for Ruby installation was rvm install 2.1.5. Of course, when I executed brew cleanup alone, I got the same error messages,

I tried to solve the issue with brew untap as follows, but I only got error messages.

brew tap --repair didn’t help me.

brew upgrade calls brew cleanup, and it failed.


Uninstall and reinstall Homebrew. After Homebrew reinstallation, there’s no need of other configurations.


After executing the command, you will get the question, “Are you sure you want to uninstall Homebrew? This will remove your installed packages!” and press y and proceed.


The Ruby was easily installed with rvm install 2.1.5 after Homebrew reinstallation.


Some application disappeared. So I had to reinstall them.


Reinstalled with brew install postgresql. The data did not disappear.


Reinstalled with brew install mysql. The data did not disappear.


Reinstalled with brew install mongo. The data did not disappear.


Reinstalled with brew install pyenv. Installed Python did not disappear.

R, RStudio

Reinstalled with brew cask install r rstudio.

Condition for the error

If you upgraded macOS to Mojave after Homebrew installation, the error can appear. I was in the same situation.