After some drive juggling [cloning to HFS+ then re-cloning back] to fix an error on my APFS boot drive, I'm now in the position where I no longer have any partition with a Recovery volume.
Carbon Copy Cloner offered to create one when I first made the clone, but as I was squeezing this into a tight space on a drive with several partitions on it already, including one with an MBR wrapper, the operation failed.
Due to further, unforeseen issues, I also had to sacrifice my Time Machine drive, so I now have no direct source to copy a Recovery Partition from.
I'm on a Mac Pro 4,1/5,1 macOS 10.13.5, which will not boot to Internet Recovery.
Is there any way to create one, hopefully without reinstalling the OS?
Alternatively, will running the OS installer directly from the App Store "live" [ie launching it from the running Finder] over the top of the existing OS do the trick?
I will, at that point, have 2 bootable OS partitions on 2 separate drives, so potentially I could run the update to one from the other, if that will gain anything.
There are many previous questions on Ask Different regarding this, but none recent enough to cover APFS.
Best Answer
I'm still open to quicker ways to do this, however, I managed to solve it by running the full High Sierra installer over the drive.
Get the installer from the App Store. You need to use search as it doesn't appear in your Purchase History.
Run the installer - for some reason it insists on doing the Firmware update again, even though that had already been done.
Note: It says to hold the power button 'until the light flashes or you hear a tone'. Empirically, waiting for the tone is more likely to succeed. Releasing the button when the light flashes isn't guaranteed to work. If you hold for a few seconds after the tone is heard, the machine will automatically boot anyway.
The install took about 45 minutes in total.
Recovery Partition was restored.