执行：
gw@ubuntu:/$ /etc/init.d/networking restart
报错：
stop: Rejected send message, 1 matched rules; type="method_call", sender=":1.7" (uid=1000 pid=1201 comm="stop networking ") interface="com.ubuntu.Upstart0_6.Job" member="Stop" error name="(unset)" requested_reply="0" destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init ")
start: Rejected send message, 1 matched rules; type="method_call", sender=":1.8" (uid=1000 pid=1195 comm="start networking ") interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)" requested_reply="0" destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init ")
原因：
需要root权限。
Ubuntu14.04修改配置，重启网卡没有生效，出现如下问题：
service networking restart //重启网络服务
报错：
stop: Job failed while stopping
start: Job is already running: networking
tail -f /var/log/upstart/networking.log //查看错误日志
Stopping or restarting the networking job is not supported.
Use ifdown & ifup to reconfigure desired interface.
解决：
ifdown eth0 && ifup eth0