apt-get update 总是报错

W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_elementary-os_testing_ubuntu_dists_trusty_main_binary-amd64_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_elementary-os_testing_ubuntu_dists_trusty_main_binary-i386_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_elementary-os_daily_ubuntu_dists_trusty_main_binary-amd64_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_elementary-os_daily_ubuntu_dists_trusty_main_binary-i386_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_elementary-os_os-patches_ubuntu_dists_trusty_main_binary-amd64_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_elementary-os_os-patches_ubuntu_dists_trusty_main_binary-i386_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_vala-team_ppa_ubuntu_dists_trusty_main_binary-amd64_Packages Hash 校验和不符
W: 无法下载 bzip2:/var/lib/apt/lists/partial/ppa.launchpad.net_vala-team_ppa_ubuntu_dists_trusty_main_binary-i386_Packages Hash 校验和不符
E: Some index files failed to download. They have been ignored, or old ones used instead.
我已经删除 /var/lib/apt/lists/* N 次了，并且apt-get clean N次了，但是每次都报这种错误。
关键是这没办法换源啊，有大神知道这方面要怎么解决吗？？？？