title: How exactly mvn -U works?
body: <p>I want to know what exactly Maven do in the -U phase.</p>
  
  <p>The argument ordering forced check for updates on remote repositories and if needed, updating the local maven repository with the updated dependencies used in our project.</p>
  
  <p>As described:</p>
  
  <pre><code>-U --update-snapshots Forces a check for updated releases and snapshots on remote repositories
  </code></pre>
  
  <p>But, how exactly is this done? Is maven first of all downloading all the remote repositories and locally decides that they need to get updated, or, deciding without downloading them first? Is there some corner cases that should be known?</p>
  
  <p>My Maven version is:</p>
  
  <pre><code>Apache Maven 3.2.2 (45f7c06d68e745d05611f7fd14efb6594181933e; 2014-06-17T16:51:42+03:00)
  Maven home: /usr/local/Cellar/maven/3.2.2/libexec
  Java version: 1.7.0_60, vendor: Oracle Corporation
  Java home: /Library/Java/JavaVirtualMachines/jdk1.7.0_60.jdk/Contents/Home/jre
  Default locale: en_US, platform encoding: UTF-8
  OS name: "mac os x", version: "10.9.4", arch: "x86_64", family: "mac"
  </code></pre>