I have an external disk which I used to boot from, but I can't remember which version of macOS is installed. Where do I look in the directories to determine which version is installed? I am not booted into it, and I don't want to boot in yet, so can't just look in About this Mac. The System folder itself is dated 22 March 2022 so it's quite recent.
Mac mini, macOS 12.5
In the following location where you replace <Volume Name> with the drive name:
plutil -p /Volumes/<Volume Name>/System/Library/CoreServices/SystemVersion.plist
Output will have this format based on my current 12.5 installation:
{
"iOSSupportVersion" => "15.6"
"ProductBuildVersion" => "21G72"
"ProductCopyright" => "1983-2022 Apple Inc."
"ProductName" => "macOS"
"ProductUserVisibleVersion" => "12.5"
"ProductVersion" => "12.5"
}
In the following location where you replace <Volume Name> with the drive name:
plutil -p /Volumes/<Volume Name>/System/Library/CoreServices/SystemVersion.plist
Output will have this format based on my current 12.5 installation:
{
"iOSSupportVersion" => "15.6"
"ProductBuildVersion" => "21G72"
"ProductCopyright" => "1983-2022 Apple Inc."
"ProductName" => "macOS"
"ProductUserVisibleVersion" => "12.5"
"ProductVersion" => "12.5"
}
Found an easy way! Since the disk is connected to the Mac, go in to System Preferences and choose Startup Disk. Click the lock to make changes, and put the computer's password in.
Then all the bootable disks will be shown, and below each one is the version of macOS installed.
Find the one you want to know about and note the version, then just cancel out of changing the Startup Disk.
You can also just use "Get Info" on the mounted volume which will mention the OS on the drive. I forget if this still works with macOS 10.15+ with the separate system & data volumes. I'm sure if you "Get Info" on the system volume that it would include the information, not sure if the same is true of the "Data" volume.
How to identify macOS version by looking in directories
