brew 安装权限问题求救。

mac 新手，使用 brew 安装 telnet，可是安装过程提示如下：

Error: The following directories are not writable by your user:
/usr/local/lib

You should change the ownership of these directories to your user.
  sudo chown -R $(whoami) /usr/local/lib

And make sure that your user has write permission.
  chmod u+w /usr/local/lib

既然当前用户没有写入权限，那么 sudo 或者切换至 root 安装吧，也不行，不过这个错误倒起码是很中肯：

Error: Running Homebrew as root is extremely dangerous and no longer supported.
As Homebrew does not drop privileges on installation you would be giving all
build scripts full access to your system.

但是据我对 linux 的使用经验，/usr/local/lib 理应由系统掌控，直接这么简单粗暴的把系统目录改成当前用户，有所不当吧，虽然这个应该不会有什么影响。或者是我对 brew 的理解不够，有其他的地方可以配置？还请大家指教。谢谢。