尝试在我的Mac上运行我的第一个rails应用时，我一直有访问被拒绝的错误。
当我运行bundle install时，我得到了
An error occurred while installing pg (0.18.1), and Bundler cannot continue.
Make sure that `gem install pg -v '0.18.1'` succeeds before bundling.
然后我运行gem install pg -v '0.18.1'并收到以下错误
Building native extensions. This could take a while...
ERROR: Error installing pg:
ERROR: Failed to build gem native extension.
/Users/foo/.rvm/rubies/ruby-2.2.1/bin/ruby -r ./siteconf20150502-79500-1qqztpf.rb extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
--with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Gem files will remain installed in /Users/foo/.rvm/gems/ruby-2.2.1/gems/pg-0.18.1 for inspection.
Results logged to /Users/foo/.rvm/gems/ruby-2.2.1/extensions/x86_64-darwin-14/2.2.0-static/pg-0.18.1/gem_make.out