I would like to use my existing external ssd (500GB) as a bootable Mojave installation disk. But I don't want to erase the contents or format the drive.
This page has the general instructions https://support.apple.com/en-us/HT201372 for doing that.
createinstallmedia does not have an option for what I am looking for. Arguments are:
Arguments --volume, A path to a volume that can be unmounted and erased to create the install media. --nointeraction, Erase the disk pointed to by volume without prompting for confirmation. --downloadassets, Download on-demand assets that may be required for installation.
Actually, I have done this before. The target ssd has bootable Sierra installation media on it, then why this post you say? Unfortunately, I can not remember the exact steps I have taken.
Maybe-related files/folders on the Sierra disk:
.DocumentRevisions-V100 .fseventsd .IABootFiles .IABootFilesSystemVersion.plist .IAPhysicalMedia .Spotlight-V100 .TemporaryItems .Trashes Install macOS Sierra Library System usr
While tackling the problem, I created an empty dmg of 12GB, mounted and used
createinstallmedia over it.
The files/folders are as follows:
.DocumentRevisions-V100 .fseventsd .IAPhysicalMedia .metadata_never_index .TemporaryItems .VolumeIcon.icns Install macOS Mojave Library System usr