centos7 yum源不能使用的解决方法

在/etc/yum.repos.d下面添加 Centos-Base.repo

内容为：

#CentOS-Base.repo

#The mirror system uses the connecting IP address of the client and the

#update status of each mirror to pick mirrors that are updated to and

#geographically close to the client. You should use this for CentOS updates

#unless you are manually picking other mirrors.

#If the mirrorlist= does not work for you, as a fall back you can try the

remarked out baseurl= line instead.

[base]
name=CentOS-7 - Base - aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7.5.1804/os/$basearch/
gpgcheck=0
enabled=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7

[updates]
name=CentOS-7 - Updates - aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7.5.1804/updates/$basearch/
gpgcheck=0
enabled=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7

[extras]
name=CentOS-7 - Extras - aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7.5.1804/extras/$basearch/
gpgcheck=0
enabled=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7

[centosplus]
name=CentOS-7 - Plus - aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7.5.1804/centosplus/$basearch/
gpgcheck=0
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7

[contrib]
name=CentOS-7 - Contrib - aliyun.com
baseurl=http://mirrors.aliyun.com/centos/7.5.1804/contrib/$basearch/
gpgcheck=0
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7

如果不能认识域名，记得添加域名，在/etc/resovle.conf里添加
#nameserver
search localdomain
nameserver 8.8.8.8