$ sudo apt-get update
...
W: Failed to fetch http://ppa.launchpad.net/hzwhuang/ss-qt5/ubuntu/dists/trusty/main/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://archive.canonical.com/ubuntu/dists/trusty/partner/source/Sources Hash Sum mismatch
W: Failed to fetch http://archive.canonical.com/ubuntu/dists/trusty/partner/binary-amd64/Packages Hash Sum mismatch
W: Failed to fetch http://archive.canonical.com/ubuntu/dists/trusty/partner/binary-i386/Packages Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.
首先启动全局代理再update一下，如果仍然有错尝试下面的命令：
sudo apt-get clean
sudo apt-get autoclean
sudo apt-get autoremove
sudo rm -rf /var/lib/apt/lists/*
再次执行sudo apt-get update如果错误依然存在，
将apt-get升级到最新版本(for Ubuntu 14.04)：
curl -s https://packagecloud.io/install/repositories/computology/apt-backport/script.deb.sh | sudo bash
sudo apt-get install apt=1.2.10
再次执行sudo apt-get update如果错误依然存在，按照报错的内容，
在/etc/apt/sources.list文件中注释掉了包含canonical的项，
在/etc/apt/sources.list.d/下把hzwhuang-ss-qt5-trusty.list
重命名为hzwhuang-ss-qt5-trusty.list.old，再次执行sudo apt-get update通过。