apt-get update 过期

refs:

http://unix.stackexchange.com/questions/2544/how-to-work-around-release-file-expired-problem-on-a-local-mirror

apt-get update 过期,

E: Release file for http://ftp.at.debian.org/debian-backports/dists/squeeze-backports/Release is expired (invalid since 1d 4h 40min 18s). Updates for this repository will not be applied.

等待源修复，或者暂时不检查有效性.

sudo apt-get -o Acquire::Check-Valid-Until=false update