检测网络连接

        通过ping常见网站，看返回是否正常,比如百度

ping www.baidu.com

如果不能ping通，可能是网络配置问题。检测操作系统网络配置

检测DNS

        如果你的网络连接正常，可能是DNS问题。

        编辑/etc/resolv.conf文件，确保其中包含有效的DNS服务器：

vi /etc/resolv.conf

         加入下面内容：

nameserver 8.8.8.8nameserver 8.8.4.4

        保存文件并退出。

    修改YUM源

        如果上述都没问题，还是无法连接，则修改YUM源

        1.备份现有源

sudo cp -r /etc/yum.repos.d /etc/yum.repos.d.backup

        2.修改文件

vi /etc/yum.repos.d/CentOS-Base.repo

        将内容替换为以下阿里源

[base]name=CentOS-$releasever - Base - mirrors.aliyun.combaseurl=http://mirrors.aliyun.com/centos/$releasever/os/$basearch/gpgcheck=1gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7 [updates]name=CentOS-$releasever - Updates - mirrors.aliyun.combaseurl=http://mirrors.aliyun.com/centos/$releasever/updates/$basearch/gpgcheck=1gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7 [extras]name=CentOS-$releasever - Extras - mirrors.aliyun.combaseurl=http://mirrors.aliyun.com/centos/$releasever/extras/$basearch/gpgcheck=1gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7 [centosplus]name=CentOS-$releasever - Plus - mirrors.aliyun.combaseurl=http://mirrors.aliyun.com/centos/$releasever/centosplus/$basearch/gpgcheck=1enabled=0gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[base]
name=CentOS-$releasever - Base - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[updates]
name=CentOS-$releasever - Updates - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[extras]
name=CentOS-$releasever - Extras - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[centosplus]
name=CentOS-$releasever - Plus - mirrors.aliyun.com
baseurl=http://mirrors.aliyun.com/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

保存文件并退出。

        3.清理缓存更新

sudo yum clean allsudo yum makecachesudo yum update

        完成