title: How to fix the MiniMagick error: 'unable to extend cache' on MacOSX?
body: <p>When I'm trying to upload a picture I receive an error message:
  This is the error message I get:</p>
  
  <pre><code>Thumbnail Failed to manipulate with MiniMagick, maybe it is not an image? 
  Original Error: 
    Command ("mogrify -resize x101163 -gravity Center -background rgba(255,255,255,0.0) -extent 118x100000 /var/folders/jk/hwpphsbx71ncw5rz6mjs21yc0000gn/T/mini_magick20131210-54787-106bvlz.png") 
  failed: {
    :status_code=&gt;1, 
    :output=&gt;
      "mogrify: unable to extend cache `/var/folders/jk/hwpphsbx71ncw5rz6mjs21yc0000gn/T/mini_magick20131210-54787-106bvlz.png': 
      No space left on device @ error/cache.c/OpenPixelCache/3638.\n"
  }
  </code></pre>
  
  <p>It seems that a certain cache somewhere is full. I also get a message from my terminal that it's full. Is there a way to clear it - without destroying anything?</p>
  
  <p>Things I've checked:</p>
  
  <ul>
  <li>My hard disk has enough storage left</li>
  </ul>