Nap for 20 minutes, then woke up suddenly even the server is not online, suspected to be a problem with the network cable, plug in the wireless network card can not be networked.
Input terminal ifconfigdisplayed as follows: 
find the ip address not become UP BROADCAST RUNNING MULTICAST.
Baidu UP BROADCAST RUNNING MULTICASTto find a solution:
sudo dhclient enp6s0
It is said to enp6s0 assigned ip address
is not on Baidu, the original DHCP protocol dhclient customer terminal 1 , which uses DHCP or BOOTP protocol or protocols used in a static address these two protocols are not used to configure one or more network interfaces .
What, what is DHCP?
DHCP (Dynamic Host Configuration Protocol, Dynamic Host Configuration Protocol) is a local area network protocol 2 , using the UDP protocol works, there are two main purposes: to automatically assign IP addresses to the internal network or Internet service provider to the user or an internal network management members as a means for central management of all computers, are described in detail in RFC 2131. DHCP has three ports, and wherein UDP67 UDP68 normal DHCP service ports, respectively, as the DHCP Server and DHCP Client service port; 546 ports for DHCPv6 Client, and not for the DHCPv4, failover for the DHCP service, which is required special open service, DHCP failover is used to make "hot standby" in. Total net should be learned can understand one about.
That problem solved?
It is said to be manually look at each boot sudo dhclient enp6s0, which is bad, how to solve?
sudo gedit /etc/network/interfaces
Modified to read as follows:
auto lo
iface lo inet loopback
auto enp6s0
iface enp6s0 inet dhcp
Restart Network
1.sudo /etc/init.d/networking restart
2.sudo service network-manager restart
knock off