报错结果：
bash-3.2# brew update
Error: Cowardly refusing to `sudo brew update`
解决方案：
顺序执行以下即可：
ls -al `which brew`
sudo chown root:wheel `which brew`
sudo chown : `chown brew`
执行结果：
bash-3.2# ls -al `which brew` -rwxr-xr-x 1 huanghonglin admin 791 10 26 15:57 /usr/local/bin/brew bash-3.2# sudo chown root:wheel `which brew` bash-3.2# sudo chown : `chown brew` usage: chown [-fhv] [-R [-H | -L | -P]] owner[:group] file ... chown [-fhv] [-R [-H | -L | -P]] :group file ... usage: chown [-fhv] [-R [-H | -L | -P]] owner[:group] file ... chown [-fhv] [-R [-H | -L | -P]] :group file ... bash-3.2# brew update Updated Homebrew from eabf890b to ec15ed4a. ==> New Formulae appledoc postgrest walkmod docker-machine-parallels unicorn ==> Updated Formulae appscale-tools docker-machine epubcheck libressl sonar caf docker-swarm fzf logtalk sqlite cake elasticsearch git macvim dmd embulk jpeg-turbo monetdb docker-compose entr kubernetes-cli pyenv ==> Renamed Formulae cyassl -> wolfssl
更新OS X El Capitan系统后，brew update报错，解决方案
原文：http://www.cnblogs.com/S-yesir/p/4942431.html