title: Exclusive\Synchronized access to a file (Queuing)
body: <p>We have a shared folder which contains some files that needs to be processed.
  We also have 3 UNIX servers which runs a shell script which take and process one file each time. At the end of the script the file it's moved away.
  The 3 UNIX server doesn't communicate each other, and they are not aware of each other.</p>
  
  <p>In your opinion what is the best way to guarantee that each file will be processed one time, without raising concurrent access issues\error ?</p>