Installing a Depreciated version of Apple OSX

DustinB3403

If you ever have to do this in your career you may find out it's a bit of a pain in the rear. Apple really wants everyone current but in practical terms, running an OS like Catalina may not work for your business, not until Apple fixes the bugs.

So what are you to do, you can't download the ISO's any more (normally) and if you do have a bootable USB with the OS you want on it, it says the file is corrupted and can't be used.

While don't believe that.

Turn off your WiFi and make sure that you aren't connected to the internet.

Plug in your bootable USB
Reboot the laptop, while holding Option
Select the USB boot disk and get into the install environment
Click on Utilities and open Terminal
Enter something along these lines date -u 1204194418 (see below for details)
Exit Terminal
Select the "Upgrade Mac OS" option which should have the Mojave, Catalina or whatever OS you are wanting to install as the thumbnail

What were doing is making the system think it's a year or more out from what it actually is, as the ISO's simply have a lifespan that Apple uses to force you onto the latest and greatest.

Running date -u 1204194418 which is explained like this date -u {month}{day}{hour}{minute}{year} so the example there changes the time to Dec 4, 19:44, 2018. Exit the terminal and get back to the boot selection, tap "Upgrade OSX" now you're able to install that depreciated version of OSX on your laptop and keep your fleet congruent.

*Edited for process clarity

WLS-ITGuy

We have a few Mac users who do a lot of Adobe work. I was testing MacOS Catalina and found it was a shithole of an OS. So buggy! I was able to download Mojave but really wanted to go back to High Sierra and couldn't. I really think High Sierra was the best one yet.

DustinB3403

@WLS-ITGuy give this a try, you may need to go back more than a year though.