How do I remove my network from the recovery partition before sale?

Question

I'm about to put my old MBP up for sale, so I re-installed from the recovery partition after wiping the drive. But when I rebooted from the recovery partition to double-check I'd deleted everything, it connected to my wifi network. I've got two questions:

1. How do I remove my network credentials from the recovery partition?
2. What other personal information is it storing without my knowledge, and how do I wipe it?

Answer 1

The answer was indeed to reset the NVRAM by holding cmd-alt-p-r during boot. Cheers :)

Answer 2

In recent versions of macOS, the installer will boot into the setup which copies the NVRAM Wi-Fi credentials to a preferences file. Then, even if you clear the NVRAM, on the next boot, the OS will copy the Wi-Fi credentials back to the NVRAM.

To get around this:

1. After installation, shut down by pressing Cmd-Q
2. Boot into recovery mode (hold Cmd-R during boot)
3. Open the Terminal from Utilities menu > Terminal
4. Remove the wi-fi preferences (assuming your volume is named Macintosh HD:

   cd '/Volumes/Macintosh HD/Library/Preferences/SystemConfiguration/'
   # For 10.15 and earlier:
   rm com.apple.airport.preferences.plist
   # For 11.x (Big Sur) and later:
   rm com.apple.wifi.known-networks.plist
   

5. Clear the nvram variables:

   nvram -d current-network
   nvram -d preferred-networks
   nvram -d preferred-count
   

6. Reboot the computer into setup assistant. Now it will not know the network.