Bootable USB Thumb Drive

Yes you can, just as long as each bootable installer is on its own partition. Just make sure the drive is big enough to handle the size of all the installers. Open Disk Utility. Click on "View". Select "Show All Devices. Select the USB drive, not the volume below it. Click on "Erase" in the top tool bar. Select Scheme: GUID Partition Map, and Format: MacOS Extended (Journaled). Click on "Erase" in the lower right of the drop down window. After that is done, click on "Partition", and add the number of partitions you want, Click on "Apply".

How to create a bootable installer for macOS - Apple Support

At less than $30 for a pack of ten 16 GB USB flash drives and variously less, hardly seems worth the effort. Particularly when accounting for the extra effort in creating and maintaining all of that, and cycling off the older installers as they age out. Or losing all of your installers together if the omnibus USB drive is lost or fails. But sure. Should work.

Unfortunately, full installers are no longer made available for download from app store. If you download the installer from the page in app store that you are be re-directed to by following the support page link, it will yield a ‘stub’ installer that is approximately 19 mb in size—not the full 5.23 gb (approximate) installer required in order to create a bootable installer. If you attempt to create a bootable installer via Terminal with the stub installer, you will receive an error message upon fail that reads: “‘MyVolume’ (or whatever you name the usb installer disk) does not appear to be a valid installer”.

ednarcoleptic wrote:

Unfortunately, full installers are no longer made available for download from app store. If you download the installer from the page in app store that you are be re-directed to by following the support page link, it will yield a ‘stub’ installer that is approximately 19 mb in size—not the full 5.23 gb (approximate) installer required in order to create a bootable installer. If you attempt to create a bootable installer via Terminal with the stub installer, you will receive an error message upon fail that reads: “‘MyVolume’ (or whatever you name the usb installer disk) does not appear to be a valid installer”.

Just run the stub installer so it downloads the rest of the full installer. Once the 2nd download finishes just quit the installer. Then you can create the bootable USB drive.

The 2nd download (i.e. package contents that include createinstallmedia) creates a separate folder (‘Mac os Install’ I think?) that is downloaded to user folder. But the terminal command for createinstallmedia points to the installer (stub installer which does not contain the package files). The terminal command needs to be modified, then, doesn’t it?

I have never had any trouble downloading a full installer, although I have read that many people do just get the stub installer. I do not know why.