title: Resize image using mini_magick, but no file in /tmp directory
body: <p>I'm using the carrier_wave and mini_magick gems along with ImageMagick in a Rails app. All versions are as current as can be. </p>
  
  <p>It works fine in development mode. However, I just deployed the app and it does not work in production mode.</p>
  
  <p>The problem occurs when I request mini_magick to resize an image:</p>
  
  <pre><code>rake aborted!
  No such file or directory - gm identify -ping /tmp/mini_magick20120407-19273-jjzz44.jpg
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/subexec-0.2.1/lib/subexec.rb:71:in `spawn'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/subexec-0.2.1/lib/subexec.rb:71:in `spawn'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/subexec-0.2.1/lib/subexec.rb:55:in `run!'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/subexec-0.2.1/lib/subexec.rb:41:in `run'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:405:in `run'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:399:in `run_command'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:198:in `valid?'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:163:in `create'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:73:in `read'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:134:in `block in open'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:133:in `open'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/mini_magick-3.4/lib/mini_magick.rb:133:in `open'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/carrierwave-0.6.0/lib/carrierwave/processing/mini_magick.rb:245:in `manipulate!'
  /usr/local/rvm/gems/ruby-1.9.3-p125/gems/carrierwave-0.6.0/lib/carrierwave/processing/mini_magick.rb:145:in `resize_to_fit'
  </code></pre>
  
  <p>When I comment out the CarrierWave request to 'resize_to_fit' the image everything works fine.</p>
  
  <p>I've read where mini_magick had some problems with a race condition
  where the files in the /tmp directory were being deleted by the
  garbage collector before mini_magick could process them, but those
  cases seemed to deal with large images and/or cloud storage.</p>
  
  <p>My image file is only 6K and everything is local, so I find it hard to
  believe that the garbage collector is swooping in and deleting
  the /tmp file before it can be resized. (But then again, I have no
  idea of the timing of these things, so I could be wrong.)</p>
  
  <p>Can anyone help me with this?</p>
  
  <p>Thanks,
  Larry </p>