Centos7更新yum源
1、备份原有yum源
$ mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
2、选择可用的yum源
# 阿里云
$ wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
# 163
$ wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.163.com/.help/CentOS7-Base-163.repo
3、生成缓存
$ yum clean all # 清除yum缓存
$ yum makecache # 重建缓存
$ yum -y update # 升级所有包
