很多源已经停止服务了
cd /etc/yum.repos.d

CentOS-Base.repo

# 原来的都加上 enable=0 

[base]
name=CentOS-$releasever - Base - mirrors.aliyun.com
failovermethod=priority
baseurl=http://mirrors.aliyun.com/centos/$releasever/os/$basearch/
        http://mirrors.aliyuncs.com/centos/$releasever/os/$basearch/
        http://mirrors.cloud.aliyuncs.com/centos/$releasever/os/$basearch/
gpgcheck=1
enable=0
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

# 最后加上如下配置
# Vault

[Vault-base] 
name=Vault-CentOS-$releasever - Base 
baseurl=http://vault.centos.org/centos/$releasever/os/$basearch/ 
gpgcheck=1 
# gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-$releasever
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[Vault-updates] 
name=Vault-CentOS-$releasever - Updates 
baseurl=http://vault.centos.org/centos/$releasever/updates/$basearch/ 
gpgcheck=1 
# gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-$releasever
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

[Vault-extras]
name=Vault-CentOS-$releasever – Extras 
baseurl=http://vault.centos.org/centos/$releasever/extras/$basearch/ 
gpgcheck=1 
# gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-$releasever
gpgkey=http://mirrors.aliyun.com/centos/RPM-GPG-KEY-CentOS-7

epel.repo

[epel]
name=Extra Packages for Enterprise Linux 7 - $basearch
enabled=1
failovermethod=priority
baseurl=https://mirrors.vcea.wsu.edu/centos-vault/epel-7/$basearch
# baseurl=http://mirrors.cloud.aliyuncs.com/epel/7/$basearch
gpgcheck=0
gpgkey=http://mirrors.cloud.aliyuncs.com/epel/RPM-GPG-KEY-EPEL-7