brew update in MAC EI Capitan Issue

最近想在[mac]上面安裝[mongodb]使用，
怎知道準備安裝時就出現問題，

brew update issue

$ brew update
Error: The /usr/local directory is not writable.
Even if this directory was writable when you installed Homebrew, other
software may change permissions on this directory. Some versions of the
"InstantOn" component of Airfoil are known to do this.

You should probably change the ownership and permissions of /usr/local
back to your user account.
  sudo chown -R $(whoami):admin /usr/local

趕緊搜尋了一下，原來和我最近更新os到EI Capitan 10.11有關。

Solution

$   sudo chown -R $(whoami):admin /usr/local

Reference: http://apple.stackexchange.com/questions/208944/upgrading-brew-in-el-capitan