centos 运行yum makecache生成缓存有时候会出现这个问题，
Not using downloaded repomd.xml because it is older than what we have
解决方法：清空/var/cache/yum/目录下面的文件

rm -rf /var/cache/yum/*

centos 运行yum makecache生成缓存有时候会出现这个问题，
Not using downloaded repomd.xml because it is older than what we have
解决方法：清空/var/cache/yum/目录下面的文件

rm -rf /var/cache/yum/*