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I try to install Mojave on a Mac with Catalina running. I have generated a second drive and downloaded the "install macOS" application. Unfortunately the installer is not opened. The error message says "This copy of the "install macOS application is too old to be opened on this version of macOS".
What's next?
Mac Pro, macOS 10.13
I reverted to Mojave from Catalina by creating a USB installer, I used this guide which uses terminal and doesn't require any other programs:
http://osxdaily.com/2018/09/26/make-macos-mojave-boot-usb-installer/
It worked perfectly on my late 2015 iMac Retina 5K.
I reverted to Mojave from Catalina by creating a USB installer, I used this guide which uses terminal and doesn't require any other programs:
http://osxdaily.com/2018/09/26/make-macos-mojave-boot-usb-installer/
It worked perfectly on my late 2015 iMac Retina 5K.
I don't know the manufacture year of your Mac but no Mac can run an OS that predates the OS it originally shipped with. So be sure it's capable of running the OS.
That said, the El Captan install may be an older version with an outdates certificate. This link is for an updated version of the installer certificate:
Also, here is the installer for Mojave:
To create a bootable install drive you can use DiskMaker X:
Thanks. This seems to be the correct answer. However, it does still not work.
I have a bootable drive with El Capitain on it. I have installed it a few times. Now, the computer boots, but tries to install El Capitain. Then it tells, the image was corrupt.
I have tried another existing drive with 10.9.3 on it. This one does not recognise the new volume on the AFPS drive and claims also the Mojave installer was corrupt.
Is there a possibility to generate a bootable USB drive with Mojave on it?
Thank you for helping. The procedure was completed like the more clumsy one recommended by Apple. After creating the volume, I tried to boot as usual and it went wrong as usual. But one of my screens had a little flash. So I removed the other screens from the computer, and the procedure was perfect.
I have lost some weeks and many many hours of work because the bootable volume would not boot. But the reason was that the computer could not decide which screen to take. The culprit seems to be a procedure by booting. It happens about every third time that the order of the screens gets lost. Then all windows opened in the first screen are pushed to the end of the last. One can pull them out one by one. I have reported the issue multiple times to Apple. No help.
Thanks again. Now my computer has two MacOS.
You will have to put your Mojave install onto a thumb drive, it must be bootable. Then you can boot from the USB drive and install from there. You may need to reformat the hard drive.
How to install Mojave after Catalina
