How to check whether centos is connected to the Internet

How to check whether centos is connected to the Internet?

1. ifconfig command.

Check if there is any problem with the network configuration

Configure the network in /etc/sysconfig/network-scripts/ifcfg-ens33, remember onboot=onThis option must be set, otherwise the network cannot start

onboot=yes

IPADDR=192.168.1.31
   NETMASK=255.255.255.0
   GATEWAY=192.168.1.1

Remember to restart after configuring

[root@localhost ~]# /etc/init.d/network stop
[root@localhost ~]# /etc/init.d/network start

Orservice network restart

Failed to restart the network service Failed to start LSB: ...

Use the ip addr command to view the current MAC address

Change HWADDR Change ="00:0c:29:7e:67:f7" to the current mac address

2. Ping the local machine 127.0.0.1 (If it can be pinged, it means the TCP/IP protocol is correct) (PS: Ctrl C key to interrupt the ping command)

3. Check whether the ping gateway is accessible. ping 114.114.114.114

Modify dns
[root@localhost ~]# vi /etc/resolv.conf
Add two dns in it:
nameserver 114.114.114.114
nameserver 8.8.8.8

4. In the process of using CentOS7, I found that there are many differences between the network part and CentOS6.

（1）CentOS7默认使用NetworkManager管理系统的网络而不再是network
   （2）NetworkManager默认使用的是nmtui或nmcli进行管理，不再是sysconfig中的ifcfg配置文件，但这些ifcfg文件依然被支持
   （3）默认NetworkManager和network同时在系统中工作，但NetworkManager要先于network启动
   （4）实际使用过程中发现即使在ifcfg配置文件中使用了静态IP地址以及静态DNS，在NetworkManager中依然使用自动获取（DHCP）的方式，自动获取IP地址和DNS服务器地址
   （6）NetworkManager默认使用ip命令来配置网络而不是ifcfgxxx，ip命令配置的网络重启后失效
   （7）关闭NetworkManager 
          临时关闭：service  NetworkManager stop
          永久关闭：chkconfig NetworkManager off

Related references: centOS tutorial

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