我正试图在Mountain Lion上安装GraphicsMagick，但遇到了问题。我尝试了所有在博客和其他stackoverflow问题中搜索到的方法，但都没有起作用。因此，我把每个命令得到的完整错误堆栈放在这里，请查看并帮助我解决。
当我运行：
当我运行：
brew install graphicsmagick
我明白了
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'
并且
Warning: Could not link libpng. 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 libpng'
最后，我得到了以下结果：
==> make install
Warning: Could not link graphicsmagick. 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 graphicsmagick'
Possible conflicting files are:
==> Summary
/usr/local/Cellar/graphicsmagick/1.3.18: 283 files, 10M, built in 52 seconds
现在，如果我尝试brew link jpeg或brew link libpng，我会得到这个错误
Linking /usr/local/Cellar/jpeg/8d... Warning: Could not link jpeg. Unlinking...
Error: Could not symlink file: /usr/local/Cellar/jpeg/8d/bin/wrjpgcom
Target /usr/local/bin/wrjpgcom already exists. You may need to delete it.
To force the link and overwrite all other conflicting files, do:
brew link --overwrite formula_name
To list all files that would be deleted:
brew link --overwrite --dry-run formula_name
brew link --overwrite jpeg的覆盖方法，它可以工作。但是'brew link --overwrite libpng'会得到以下结果。Linking /usr/local/Cellar/libpng/1.5.14... Warning: Could not link libpng. Unlinking...
Error: Permission denied - /usr/local/share/man/man5/png.5
之后，当我尝试运行brew link graphicsmagick时，我收到以下提示：
Linking /usr/local/Cellar/graphicsmagick/1.3.18... Warning: Could not link graphicsmagick. Unlinking...
Error: Could not symlink file: /usr/local/Cellar/graphicsmagick/1.3.18/share/man/man5/quantize.5
/usr/local/share/man/man5 is not writable. You should change its permissions.
请帮忙，谢谢！
brew doctor命令会告诉你什么？ - Cedric Han