如果某台Linux(CentOS)服务器ping域名, 如下提示:
# ping www.sina.com
ping: unknown host www.sina.com

确认网络没问题的情况下, 可以通过如下步骤寻找解决办法:
1) 确认设置了域名服务器

    # cat /etc/resolv.conf
    nameserver 8.8.8.8    #(Google的公共DNS服务)
    nameserver 8.8.4.4    #(Google的公共DNS服务)

2) 确认网关已设置/确认路由表正常

    # netstat -rn
    Kernel IP routing table
    Destination Gateway Genmask Flags MSS Window irtt Iface
    0.0.0.0 10.10.10.1 0.0.0.0 UG 0 0 0 eth0

   如果未设置, 则通过如下方式增加网关:
   # route add default gw 10.245.75.1

   # grep GATEWAY /etc/sysconfig/network-scripts/ifcfg*
   /etc/sysconfig/network-scripts/ifcfg-eth0:GATEWAY=10.245.75.1

3) 确认可用dns解析

   # grep hosts /etc/nsswitch.conf
   hosts:      files dns


以上的1) 2) 3) 点只是确认问题,个人喜欢手工编写配置文件,一次解决问题。
   配置/etc/sysconfig/network-scripts/ifcfg-eth0文件后,重启network服务:
   vim /etc/sysconfig/network-scripts/ifcfg-eth0
   DEVICE="eth0"
   NM_CONTROLLED="yes"
   ONBOOT=yes
   TYPE=Ethernet
   BOOTPROTO=static
   IPADDR=10.245.75.240
   #PREFIX=24
   GATEWAY=10.245.75.1
   DNS1=8.8.8.8
   DNS2=8.8.4.4
   DEFROUTE=yes
   IPV4_FAILURE_FATAL=yes
   IPV6INIT=yes
   NAME="System eth0"
   UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx # uuid
   HWADDR=xx:xx:xx:xx:xx:xx                  # hwaddr
   NETWORKING=yes

   # service network restart