Linux下查看DNS服务器IP地址

1.最常用的方法是检查 /etc/resolv.conf 的内容：

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 221.131.143.69
nameserver 112.4.0.55
nameserver 127.0.1.1

但有时候这个文件会是空的。。

比如，在Ubuntu上，如果使用 network manager配置网络，默认的情况下， /etc/resolv.conf是空的。

运行命令 dhclient eth0/wlan0 可以刷新这个文件。

2. 使用network manager的命令行工具

$ nmcli dev list iface wlan0
GENERAL.DEVICE:                         wlan0
GENERAL.TYPE:                           802-11-wireless
GENERAL.VENDOR:                         Realtek Semiconductor Co., Ltd.
GENERAL.PRODUCT:                        RTL8188CE 802.11b/g/n WiFi Adapter
GENERAL.DRIVER:                         rtl8192ce
GENERAL.DRIVER-VERSION:                 3.13.0-48-generic
GENERAL.FIRMWARE-VERSION:               N/A
GENERAL.HWADDR:                         EC:55:F9:BF:7C:16
GENERAL.STATE:                          100 (connected)
GENERAL.REASON:                         0 (No reason given)
GENERAL.UDI:                            /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlan0
GENERAL.IP-IFACE:                       wlan0
GENERAL.NM-MANAGED:                     yes
GENERAL.AUTOCONNECT:                    yes
GENERAL.FIRMWARE-MISSING:               no
GENERAL.CONNECTION:                     /org/freedesktop/NetworkManager/ActiveConnection/1
CAPABILITIES.CARRIER-DETECT:            no
CAPABILITIES.SPEED:                     150 Mb/s
CONNECTIONS.AVAILABLE-CONNECTION-PATHS: /org/freedesktop/NetworkManager/Settings/{4}
CONNECTIONS.AVAILABLE-CONNECTIONS[1]:   74e041fe-c57c-4c91-b68f-3556bde60ff6 | 1201-1
WIFI-PROPERTIES.WEP:                    yes
WIFI-PROPERTIES.WPA:                    yes
WIFI-PROPERTIES.WPA2:                   yes
WIFI-PROPERTIES.TKIP:                   yes
WIFI-PROPERTIES.CCMP:                   yes
WIFI-PROPERTIES.AP:                     yes
WIFI-PROPERTIES.ADHOC:                  yes
IP4.ADDRESS[1]:                         ip = 192.168.1.102/24, gw = 192.168.1.1
IP4.DNS[1]:                             221.131.143.69
IP4.DNS[2]:                             112.4.0.55
DHCP4.OPTION[1]:                        expiry = 1428593985
DHCP4.OPTION[2]:                        broadcast_address = 192.168.1.255
DHCP4.OPTION[3]:                        dhcp_message_type = 5
DHCP4.OPTION[4]:                        routers = 192.168.1.1
DHCP4.OPTION[5]:                        dhcp_lease_time = 7200
DHCP4.OPTION[6]:                        ip_address = 192.168.1.102
DHCP4.OPTION[7]:                        subnet_mask = 255.255.255.0
DHCP4.OPTION[8]:                        domain_name_servers = 221.131.143.69 112.4.0.55
DHCP4.OPTION[9]:                        network_number = 192.168.1.0
DHCP4.OPTION[10]:                       dhcp_server_identifier = 192.168.1.1

或者：

$ nm-tool  | grep DNS
    DNS:             221.131.143.69
    DNS:             112.4.0.55

3. 查看文件 /var/lib/dhcp/dhclient.leases

$ cat /var/lib/dhcp/dhclient.leases 
lease {
  interface "wlan0";
  fixed-address 192.168.1.102;
  option subnet-mask 255.255.255.0;
  option routers 192.168.1.1;
  option dhcp-lease-time 7200;
  option dhcp-message-type 5;
  option domain-name-servers 221.131.143.69,112.4.0.55;
  option dhcp-server-identifier 192.168.1.1;
  renew 4 2015/04/09 14:51:16;
  rebind 4 2015/04/09 15:41:40;
  expire 4 2015/04/09 15:56:40;
}