title: Can not start MongoDB 3.2.1 on CentOS 7
body: <p>I followed this doc to install MongoDB 3.2.1 on CentOS 7. After installing, I change the owner and group of <code>var/lib/mongo</code> and <code>var/log/mongodb/mongod.log</code> to <code>root:root</code>.</p>
  
  <p>When I start the mongodb with <code>service mongod start</code>, it just shows </p>
  
  <pre><code>Starting mongod (via systemctl):  Job for mongod.service failed. See 'systemctl status mongod.service' and 'journalctl -xn' for details.[FAILED]
  </code></pre>
  
  <p>I have run the two commands to show details. </p>
  
  <p><code>systemctl status mongod.service</code> shows </p>
  
  <pre><code>mongod.service - SYSV: Mongo is a scalable, document-oriented database.
     Loaded: loaded (/etc/rc.d/init.d/mongod)
     Active: failed (Result: exit-code) since Wen 2016-01-27 18:32:46 CST; 14s ago
    Process: 24913 ExecStart=/etc/rc.d/init.d/mongod start (code=exited, status=1/FAILURE)
   Main PID: 23711 (code=exited, status=0/SUCCESS)
  
  1月 27 18:32:45 server1 systemd[1]: Starting SYSV: Mongo is a scalable, document-oriented database....
  1月 27 18:32:45 server1 runuser[24920]: pam_unix(runuser:session): session opened for user mongod by (uid=0)
  1月 27 18:32:46 server1 mongod[24913]: Starting mongod: [FAILED]
  1月 27 18:32:46 server1 systemd[1]: mongod.service: control process exited, code=exited status=1
  1月 27 18:32:46 server1 systemd[1]: Failed to start SYSV: Mongo is a scalable, document-oriented database..
  1月 27 18:32:46 server1 systemd[1]: Unit mongod.service entered failed state.
  </code></pre>
  
  <p><code>journalctl -xn</code> shows</p>
  
  <pre><code>-- Logs begin at 日 2016-01-24 16:33:05 CST, end at Wen 2016-01-27 18:32:46 CST. --
  1月 27 18:32:15 server1 sshd[24879]: pam_succeed_if(sshd:auth): requirement "uid &gt;= 1000" not met by user "root"
  1月 27 18:32:17 server1 sshd[24879]: Failed password for root from 182.100.67.59 port 10013 ssh2
  1月 27 18:32:45 server1 sudo[24896]: root : TTY=pts/0 ; PWD=/var/log/mongodb ; USER=root ; COMMAND=/sbin/service mongod start
  1月 27 18:32:45 server1 systemd[1]: Starting SYSV: Mongo is a scalable, document-oriented database....
  -- Subject: Unit mongod.service has begun with start-up
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit mongod.service has begun starting up.
  1月 27 18:32:45 server1 runuser[24920]: pam_unix(runuser:session): session opened for user mongod by (uid=0)
  1月 27 18:32:46 server1 runuser[24920]: pam_unix(runuser:session): session closed for user mongod
  1月 27 18:32:46 server1 mongod[24913]: Starting mongod: [FAILED]
  1月 27 18:32:46 server1 systemd[1]: mongod.service: control process exited, code=exited status=1
  1月 27 18:32:46 server1 systemd[1]: Failed to start SYSV: Mongo is a scalable, document-oriented database..
  -- Subject: Unit mongod.service has failed
  -- Defined-By: systemd
  -- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
  -- 
  -- Unit mongod.service has failed.
  -- 
  -- The result is failed.
  1月 27 18:32:46 server1 systemd[1]: Unit mongod.service entered failed state.
  </code></pre>
  
  <p>I accessed the server with ssh key, no password.</p>