启动服务的时候，直接失败了。Job for mongod.service failed. See ‘systemctl status mongod.service’ and ‘journalctl -xn’ for details. 日志显示：2014-07-22T00:07:15.288+0800 ERROR: Cannot write pid file to /var/run/mongodb/mongod.pid: No such file or directory

[root[@localhost](/user/localhost) run]# systemctl status mongod.service
mongod.service - SYSV: Mongo is a scalable, document-oriented database.
   Loaded: loaded (/etc/rc.d/init.d/mongod)
   Active: failed (Result: exit-code) since 二 2014-07-22 00:21:24 CST; 1min 9s ago
  Process: 2343 ExecStart=/etc/rc.d/init.d/mongod start (code=exited, status=1/FAILURE)

7月 22 00:21:24 localhost.localdomain systemd[1]: Starting SYSV: Mongo is a scalable, document-oriented database....
7月 22 00:21:24 localhost.localdomain runuser[2347]: pam_unix(runuser:session): session opened for user mongod by (uid=0)
7月 22 00:21:24 localhost.localdomain mongod[2343]: Starting mongod: [失败]
7月 22 00:21:24 localhost.localdomain systemd[1]: mongod.service: control process exited, code=exited status=1
7月 22 00:21:24 localhost.localdomain systemd[1]: Failed to start SYSV: Mongo is a scalable, document-oriented database..
7月 22 00:21:24 localhost.localdomain systemd[1]: Unit mongod.service entered failed state.

这是什么情况呢，请大神指导下