title: installed MongoDB but can not use it(errno:111 connection refused.)
body: <p>i'm a newbie with MongoDB. i installed it using the tutorial at the <a href="http://docs.mongodb.org/manual/tutorial/install-mongodb-on-red-hat-centos-or-fedora-linux" rel="nofollow">official</a> website.<br>
  when i run the command <code>mongo</code>, i get:</p>
  
  <pre><code>MongoDB shell version: 2.6.4
  connecting to: test
  2014-10-08T01:40:35.926+0330 warning: Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused
  2014-10-08T01:40:35.927+0330 Error: couldn't connect to server 127.0.0.1:27017 (127.0.0.1), connection attempt failed at src/mongo/shell/mongo.js:146
  exception: connect failed
  </code></pre>
  
  <p>it gives me the version so i have installed mongodb correctly.(right?). </p>
  
  <p>i thought the problem could have something to do with SELinux so i <code>Disabled</code> SELinux but it didn't help.
  so how what's the problem and how do i know whether i did the installation correctly or not?
  in some of SO posts i saw a command <code>mongod</code>. whats the difference between <code>mongod</code> and <code>mongo</code> commands? when i run <code>mongod</code> i get:  </p>
  
  <pre><code>bash: mongod: command not found...  
  Similar command is: 'mongo'
  </code></pre>
  
  <p>many thanks for your help and time.</p>