运行ping时，发现ping不通
[root@www ~]# ping www.baidu.com ping: www.baidu.com: Name or service not known
如果ping域名的时候出现ping:unknown host xxx.xxx
但是ping IP地址的时候可以通的话
可知是dns服务器没有配置好，
查看一下配置文件/etc/resolv.conf，里面是否有nameserver xxx.xxx.xxx.xxx，比如使用dns服务器 nameserver 8.8.8.8，如果有，修改一个可用的dns服务器，如8.8.8.8或者4.4.4.4，保存退出即可！
当然，如果连ip都ping 8.8.8.8都ping不通的话，那么就说明网络配置有问题：可以这样解决：
1、编辑网络配置
vi /etc/sysconfig/network-scripts/ifcfg-enp0s3 #注 网络配置文件名可能会有不同，在输入到ifcfg时，可以连续按两下tab键，获取提示，比如我的机器 为 ifcfg-enp0s3
TYPE=Ethernet PROXY_METHOD=none BROWSER_ONLY=no BOOTPROTO=dhcp DEFROUTE=yes IPV4_FAILURE_FATAL=no IPV6INIT=yes IPV6_AUTOCONF=yes IPV6_DEFROUTE=yes IPV6_FAILURE_FATAL=no IPV6_ADDR_GEN_MODE=stable-privacy NAME=enp0s3 UUID=098aaea2-65b0-49b7-821d-1fe636293b46 DEVICE=enp0s3 ONBOOT=yes #### 刚打开这一行是 no ，我编辑改成了yes，只需要按 i 就能编辑，编辑完按esc退出编辑模式，然后按:wq保存文件 [注意:是英文的冒号] ZONE=public
2、重启网络服务
centos6系统下 service network restart centos7系统下[速度有点慢2秒钟左右] systemctl restart network
3、测试效果
[root@localhost ~]# ping baidu.com PING baidu.com (39.156.69.79) 56(84) bytes of data. 64 bytes from 39.156.69.79 (39.156.69.79): icmp_seq=1 ttl=53 time=39.6 ms 64 bytes from 39.156.69.79 (39.156.69.79): icmp_seq=2 ttl=53 time=78.5 ms 64 bytes from 39.156.69.79 (39.156.69.79): icmp_seq=3 ttl=53 time=71.8 ms 64 bytes from 39.156.69.79 (39.156.69.79): icmp_seq=4 ttl=53 time=136 ms ### 按 contrl键 + c键 取消
还可以自定义DNS
vi /etc/resolv.conf nameserver 8.8.8.8 nameserver 8.8.4.4
4、查看本机IP
ifconfig 安装
##### 如果查看本机，发现没有 ifconfig 命令行 [root@localhost ~]# ifconfig -bash: ifconfig: command not found [root@localhost ~]# ##### 首先确认下是否是环境变量没有ifconfig 引起。 [root@localhost ~]# ls /sbin/ifconfig ls: cannot access /sbin/ifconfig: No such file or directory [root@localhost ~]# ##### 以上确定了系统是没有安装ifconfig，下面我们来安装 ##### locale是本地语言设置问题可忽略 [root@localhost ~]# yum install ifconfig Failed to set locale, defaulting to C Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile * base: mirrors.huaweicloud.com * extras: centosx4.centos.org * updates: mirrors.huaweicloud.com No package ifconfig available. Error: Nothing to do [root@localhost ~]# ### 提示没有ifconfig安装包。我们再使用yum search ifconfig来搜索下ifconfig的相关 [root@localhost ~]# yum search ifconfig Failed to set locale, defaulting to C Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile * base: mirrors.huaweicloud.com * extras: mirror-hk.koddos.net * updates: mirrors.huaweicloud.com =================================== Matched: ifconfig ==================================== net-tools.i686 : Basic networking tools [root@localhost ~]# ##### 查看ifconfig匹配的是net-tools.i686包 yum install net-tools.i686 -y
ifconfig使用
### 使用ifconfig命令，可以查看本地IP，下面这个是 没有联网时的
[root@localhost ~]# ifconfig
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
ether 08:00:38:56:29:2c txqueuelen 1000 (Ethernet)
RX packets 95 bytes 9319 (9.1 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 104 bytes 9383 (9.1 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 152 bytes 13024 (12.7 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 152 bytes 13024 (12.7 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
### 下面这个是 联网 成功的 本机IP是 192.168.1.128
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.1.128 netmask 255.255.255.0 broadcast 192.168.1.255
inet6 fd38::3d2:a2b7:39cb:278a prefixlen 64 scopeid 0x20<link>
ether 08:00:38:56:29:2c txqueuelen 1000 (Ethernet)
RX packets 111 bytes 11112 (10.8 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 124 bytes 11293 (11.0 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 156 bytes 13368 (13.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 156 bytes 13368 (13.0 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
ip addr 命令（也可以查看本机ip）
[root@localhost ~]# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:38:56:29:2c brd ff:ff:ff:ff:ff:ff
inet 192.168.1.128/24 brd 192.168.1.255 scope global noprefixroute dynamic enp0s3
valid_lft 5226sec preferred_lft 5226sec
inet6 fd38::3d2:a2b7:39cb:278a/64 scope link noprefixroute
valid_lft forever preferred_lft forever
[root@localhost ~]#
netstat和ss命令（也可以查看本机ip）
- centos6 可以使用 netstat
- centos7 可以使用 ss -ant
5、centos6下编辑ifcfg-xxx 仍无法上网
输入ifconfig命令查看是否有内网ip地址，如果没有，那么配置一下: eth0是设备名，具体看ifconfig 显示的设备名。
ifconfig eth0 192.168.1.100 netmask 255.0.0.0 up
另外使用route命令查看一下当前的默认网关，如果没有，也配置一个，
route add default gw 192.168.1.1
配置好这两个以后，就可以正常的ping通网络了，如果还不能ping www.baidu.com,那么就要去查看dns服务器啦
参考：
https://blog.csdn.net/qq_30180559/article/details/79535596
https://jingyan.baidu.com/article/eb9f7b6d42636d869364e8c9.html
https://blog.csdn.net/menlinshuangxi/article/details/7968955