dhcp的全称是Dynamic Host Configuration Protocol
dhclient则是Dynamic Host Configuration Protocol client
使用dhclient重新在dhcp服务器攻取ip地址
dhclient -r eth0 ifconfig eth0 down ifconfig eth0 up dhclient eth0
经过上面操作，就会获取到新的ip地址。
centos6的dhclient的信息缓存在/var/lib/dhclient/dhclient-*.leases