鉴于国外的yum源经常连不上，切换成国内的yum源，我们首选阿里的，也可以是腾讯云的

备份

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

下载新的CentOS-Base.repo 到/etc/yum.repos.d/

CentOS 6

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo

CentOS 7

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

之后运行yum makecache生成缓存

yum clean all
yum makecache

CentOS-Base.repo

[extras]
name=Qcloud centos extras - $basearch 
baseurl=http://mirrors.cloud.tencent.com/centos/$releasever/extras/$basearch/
gpgcheck=1 
gpgkey=http://mirrors.cloud.tencent.com/centos/RPM-GPG-KEY-CentOS-7  
enabled=1 
metadata_expire=24h 
priority=1 

[os]
name=Qcloud centos os - $basearch 
baseurl=http://mirrors.cloud.tencent.com/centos/$releasever/os/$basearch/
gpgcheck=1 
gpgkey=http://mirrors.cloud.tencent.com/centos/RPM-GPG-KEY-CentOS-7  
enabled=1 
metadata_expire=24h 
priority=1 

[updates]
name=Qcloud centos updates - $basearch 
baseurl=http://mirrors.cloud.tencent.com/centos/$releasever/updates/$basearch/
gpgcheck=1 
gpgkey=http://mirrors.cloud.tencent.com/centos/RPM-GPG-KEY-CentOS-7  
enabled=1 
metadata_expire=24h 
priority=1 

CentOS-Epel.repo

[epel]
name=EPEL for redhat/centos $releasever - $basearch
failovermethod=priority
gpgcheck=1
gpgkey=http://mirrors.cloud.tencent.com/epel/RPM-GPG-KEY-EPEL-7
enabled=1
baseurl=http://mirrors.cloud.tencent.com/epel/7/$basearch/
metadata_expire=24h
priority=2