关于ping外网时出现unknow host的问题

静态IP设置

通过修改/etc/network/interfaces就好，参数说明直接man interfaces看就好
修改的参数可看下面第二张图。

修改过程

首先，ip地址这些是设置正确了，板子可以正常ping通PC，网关，但就是无法PING通外网。如下

根据网上搜索和自己摸索更改了dns如下，直接改resolv.conf下启动又会没了：

然后重启 ，命令如下，如果不是用NFSROOT方式启动的板子，那么一般就可以正常启动了，而且重启时可以看到输出网络重启的信息，但在nfsroot方式启动时确依然不行，显示如下

root@192:~# /etc/init.d/networking restart
Restarting networking (via systemctl): networking.service.
root@192:~# 

依网上说法直接修改：/etc/resolv.conf文件，添加两行如下，dns是依自己的PC上的IP填的。还是不行，直接PING了下DNS地址显示 如下

root@192:~# cat /etc/resolv.conf 

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)


#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

nameserver 202.96.134.133
nameserver 202.96.128.168
root@192:~# 
root@192:~# /etc/init.d/networking restart
Restarting networking (via systemctl): networking.service.
root@192:~# ping www.baidu.com
ping: unknown host www.baidu.com
root@192:~# 
root@192:~# ping 202.96.133.134
connect: Network is unreachable

然后手动加了下网关，ping dns时有变化了但还是不通，而是外网居然OK了！！！如下：

root@192:~# ping 202.96.133.134
connect: Network is unreachable

root@192:~# route add default gw 192.168.1.2
root@192:~# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.1.2     0.0.0.0         UG    0      0        0 eth0
192.168.1.0     *               255.255.255.0   U     0      0        0 eth0

root@192:~# ping 202.96.133.134
PING 202.96.133.134 (202.96.133.134) 56(84) bytes of data.
^C
--- 202.96.133.134 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 3023ms

root@192:~# ping www.baidu.com
PING www.a.shifen.com (14.215.177.38) 56(84) bytes of data.
64 bytes from 14.215.177.38: icmp_seq=1 ttl=55 time=8.20 ms
64 bytes from 14.215.177.38: icmp_seq=2 ttl=55 time=7.38 ms
64 bytes from 14.215.177.38: icmp_seq=3 ttl=55 time=6.90 ms
^C
--- www.a.shifen.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 6.904/7.499/8.206/0.537 ms
root@192:~# 

总结

1. 如果是通常的非NFSROOT启动的板子，配置好 /etc/network/interfaces就行

2. NFSROOT启动的网络文件系统：

   • 2.1 在/etc/resolv.conf中加入DNS，此处DNS是你的PC的DNS ，不是网上说的什么网关，google通用DNS等哦。。
     nameserver 202.96.134.133
     
   • 2.2 添加默认网关（网关地址看PC如上图） route add default gw 192.168.1.2
   • 2.3 重启网络

3. nfsroot启动的想联通外网就是这样了，每次都要修改/etc/resolv.conf，因为这个是动态生成的，然后还要route加网关。。。想要静态的可以查询下系统的网络加载过程，我比较懒，每个版本的linux系统都不一样，将上述步骤直接写到/etc/profile里用，OK

   if [ -f /etc/resolv.conf ];then
           echo "nameserver 202.96.134.133" >> /etc/resolv.conf
           echo "nameserver 202.96.128.166" >> /etc/resolv.conf
           /sbin/route add default gw 192.168.1.2
           /etc/init.d/networking restart
   fi
   

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另附
网络相关的配置文件interfaces说明
直接man interfaces，同样man resolv.conf

 The static Method
       This method may be used to define Ethernet interfaces  with  statically
       allocated IPv4 addresses.
       Options
              address address
                     Address (dotted quad/netmask) required
              netmask mask
                     Netmask (dotted quad or CIDR)
              broadcast broadcast_address
                     Broadcast  address  (dotted quad, + or -). Default value:
                     "+"
              metric metric
                     Routing metric for default gateway (integer)
              gateway address
                     Default gateway (dotted quad)
              pointopoint address
                     Address of other end point (dotted quad). Note the spell��‐
                     ing of "point-to".
              hwaddress address
                     Link local address.
              mtu size
                     MTU size
              scope  Address  validity  scope.  Possible values: global, link,
                     host