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
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.
从以上日志内容可以看出，传统的service重启和停止网络已经不再支持了，需要通过使用ifdown & ifup来实现相应的操作。
- 重启指定网卡
ifdown eth0 && ifup eth0
- 重启除lo网卡的所有网卡
ifdown --exclude=lo -a && sudo ifup --exclude=lo -a
- 配置桥接
# apt-get install bridge-utils
# cat /etc/network/interfaces
auto lo
iface lo inet loopback auto eth0
iface eth0 inet manual auto br0
iface br0 inet static
address 192.168.0.10
netmask 255.255.255.0
gateway 192.168.0.1
bridge_ports eth0
bridge_stp off
bridge_fd
bridge_maxwait
dns-nameservers 192.168.0.1
# ifup br0
# brctl show
bridge name bridge id STP enabled interfaces
br0 .02000a0080e1 no eth0