This was a random thing I encountered, so it bothered me until I figured out why I could not remember the password set for my System Keychain.
The reason was that I didn’t set one, and that it is randomly generated. WEP, preshared WPA keys, and other such things are kept in there. To view them, you need to have access to the keychain.
What is a geek to do? Well, clearly you have to know to perform something like the following:
sudo mv /Library/Keychains/System.keychain /Library/Keychains/System.keychain.backup sudo systemkeychain -k /Library/Keychains/System.keychain -C <a password>
where “a password” is the new keychain password that you want to give to the System keychain
Reboot the system
Bad Penny 
does this erase the old keychain or just change the password?
This would move the previous system keychain to a backup location, via the mv command and replace it with a blank keychain where the password is known.
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