我已经卸载和安装了三次Homebrew，因为它似乎永远不允许我安装任何东西，大多数安装结束时都会拒绝我的权限。
以libjpeg下载为例，我将发布当前面临的情况。
我尝试安装libjpeg并得到：
$ brew install libjpeg
==> Downloading https://downloads.sf.net/project/machomebrew/Bottles/jpeg-8d.mountain_lion.bottle.1.tar.gz
Already downloaded: /Library/Caches/Homebrew/jpeg-8d.mountain_lion.bottle.1.tar.gz
==> Pouring jpeg-8d.mountain_lion.bottle.1.tar.gz
Warning: Could not link jpeg. Unlinking...
Error: The brew link step did not complete successfully
The formula built, but is not symlinked into /usr/local
You can try again using `brew link jpeg'
Error: Permission denied - /usr/local/opt/jpeg
'brew link jpeg' 的结果是：
Error: Permission denied - /usr/local/opt/jpeg
这是我的brew doctor读取的内容
$ brew doctor
Warning: "config" scripts exist outside your system or Homebrew directories.
./configure scripts often look for *-config scripts to determine if
software packages are installed, and what additional flags to use when
compiling and linking.
Having additional scripts in your path can confuse software installed via
Homebrew if the config script overrides a system or Homebrew provided
script of the same name. We found the following "config" scripts:
/Library/Frameworks/Python.framework/Versions/2.7/bin/python-config
/Library/Frameworks/Python.framework/Versions/2.7/bin/python2-config
/Library/Frameworks/Python.framework/Versions/2.7/bin/python2.7-config
Warning: You have unlinked kegs in your Cellar
Leaving kegs unlinked can lead to build-trouble and cause brews that depend on
those kegs to fail to run properly once built. Run brew link on these:
jpeg
权限问题一直使得无法使用brew，希望能得到任何建议。