bitcoin-cli getinfo error code: -28 OSX Sierra

it seems all the other command bitcoin-cli working on my Mac,
except,  

bitcoin-cli getinfo only always returns an error.


  $ bitcoin-cli getinfo 
  error code: -28
  error message:
  Rewinding blocks...


Why does it happen?
Wait a few minutes and the error will be gone.

The source code defines error 28 as


  Client still warming up