在
brew install libmpc
我得到一个错误之后
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 libmpc'
然后我跑
brew doctor
我得到了
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: `libmpc`
所以我跑
brew link libmpc
我得到了
Error: Could not symlink file: /usr/local/Cellar/libmpc/1.0.1/lib/libmpc.dylib
/usr/local/lib/libmpc.dylib may already exist.
/usr/local/lib may not be writable.
我应该怎么办？