替换yum源

# 查看源文件
cat /etc/yum.repos.d/CentOS-Base.repo
# 可以先进行备份
cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak
# 执行替换操作
curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
# 再次查看，发现yum源已经被替换
cat /etc/yum.repos.d/CentOS-Base.repo
# 缓存
yum makecache
yum clean all