将Debian下载源同步到本地之后，通过本地资源地址进行apt update操作时提示过期问题：
E: Release file for http://localhost/security/dists/stable/updates/InRelease is expired (invalid since 1d 1h 53min 38s). Updates for this repository will not be applied.
对于该问题有三种解决方法：
1）通过cron实现定期同步。
2）零时解决方法：
aptitude -o Acquire::Check-Valid-Until=false update apt-get -o Acquire::Check-Valid-Until=false update
3）创建文件：/etc/apt/apt.conf.d/10no--check-valid-until，添加内容：
Acquire::Check-Valid-Until "0";
然后就不再提示过期警告了。
参考：
【1】https://www.bufeihua.cn/p/562249fca47d0b0001b5cc10
【2】http://unix.stackexchange.com/questions/2544/how-to-work-around-release-file-expired-problem-on-a-local-mirror