编辑：[已修复] 问题是我已经安装了它，但不知道，并尝试从源代码安装。这创建了两个版本，gem 不知道使用哪个版本。我通过转到下载的源并运行来修复它
sudo make uninstall
然后我再次运行 gem install rmagick 并且成功了！
[原来的问题]
我正在尝试安装 rmagick gem，就像在这个 railscast中一样。这是我放入 gemfile 的片段：
gem 'rmagick'
gem 'carrierwave'
当我运行 bundle install 时，我得到以下输出：
Installing rmagick (2.13.1) with native extensions
Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
/home/techusb/.rbenv/versions/1.9.3-p125/bin/ruby extconf.rb
checking for Ruby version >= 1.8.5... yes
extconf.rb:128: Use RbConfig instead of obsolete and deprecated Config.
checking for cc... yes
checking for Magick-config... yes
Warning: Found more than one ImageMagick installation. This could cause problems at runtime.
/usr/local/bin/Magick-config reports version 6.8.0 Q16 is installed in /usr/local
/usr/bin/Magick-config reports version 1.3.12 is installed in /usr
Using 6.8.0 Q16 from /usr/local.
checking for ImageMagick version >= 6.4.9... yes
checking for HDRI disabled version of ImageMagick... yes
checking for stdint.h... *** 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.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/home/techusb/.rbenv/versions/1.9.3-p125/bin/ruby
/home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:506:in `try_cpp'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:931:in `block in have_header'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:254:in `open'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
from /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/1.9.1/mkmf.rb:930:in `have_header'
from extconf.rb:193:in `<main>'
Gem files will remain installed in /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/rmagick-2.13.1 for inspection.
Results logged to /home/techusb/.rbenv/versions/1.9.3-p125/lib/ruby/gems/1.9.1/gems/rmagick-2.13.1/ext/RMagick/gem_make.out
An error occurred while installing rmagick (2.13.1), and Bundler cannot continue.
Make sure that `gem install rmagick -v '2.13.1'` succeeds before bundling.
关于这条线：
The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
我想我已经用尽了有关如何通过 google/stackoverflow 修复此错误的所有信息。我已经尝试安装开发包等。不知道从这里去哪里。非常感谢任何帮助。