Instead, install Catalina onto an EXTERNAL drive and boot and run that way if you need to fool around with Catalina. Leave Mojave installed on the INTERNAL DRIVES on BOTH your iMac and MBP.ĭO NOT 'upgrade' them to Catalina when it comes out. I'll offer you another path forward for the '32-bit issue'.

I need that USB key so I can use it on both my iMac and my Macbook Pro, so that I can boot into High Sierra or Mojave and where I can install the apps I need for work, without needing my internal drive.' 'Basically, I need a USB key with either High Sierra or Mojave on it in order for me to keep working with 32 bit apps I need for work, since I want to upgrade my main drive to Catalina when it comes out. Only thing I can think of is that there may be a problem with my Toshiba USB3 flash drive, but it seems to work just fine when I used it for other stuff. Left this one for 2 hours as well, but it just won't finish. Unfortunately, it just stops at the same moment, with 14 minutes left (sometimes switches to 13 minutes). I tried it this way because I thought the problem might be that my USB2 key is too slow. I then wiped my Time Machine partition on the external 2Tb USB3 HDD (because I want to switch from a local TM backup to a networked one, connecting the drive directly to my router instead of the iMac, and local and networked TM backups are apparently not compatible) I put the High Sierra installer on the newly created partition and booted up the installer, no problem. Tried it on the iMac and on the Macbook Pro. I left it there for over 2 hours, and nothing happens. The installer boots up just fine, but gets stuck halfway (not frozen, because when typing CMD-L, it says installation in progress). I've tried with 2 USB keys, one USB2 with 8Gb which I used to create the installer, and the other USB3 128Gb key to install High Sierra on.

I also have a mid 2015 15 inch Macbook Pro, which had Yosemite as the original OS. My iMac is a mid 2017 27 inch model, came with High Sierra installed.

Bootable usb high sierra