title: iPhone storage in tmp directory
body: <p>I have a question from <a href="https://stackoverflow.com/questions/3591421/iphone-storing-large-amounts-of-images/3591508#3591508">this stackoverflow question about iPhone storage</a>. Like I already tried to answer, we can cache data in tmp directory. But a comment says that the data can be deleted when OS whimp. I don't understand exactly the problem that the comment says. </p>
  
  <p>I want to ask if the process of OS deleting tmp directory is manually or automatically. In other words, if the system auto detect that our tmp directory has to be deleted. </p>
  
  <p>Another question is that if we can control, or be asked to do something (before the deleting process) that can help us to keep the tmp directory.</p>
  
  <p>Another question is that if we can not do anything then how often the OS will do that, under what circumstances</p>