Ubuntu12.04最新可用源

自从UBuntu升级14.04后貌似之前的163/骨头/搜狐等源都是不太行了，刚装了个wubi Ubuntu，竟然没可用源，折腾了半天，记录备忘：

   # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to  # newer versions of the distribution.  deb http://cn.archive.ubuntu.com/ubuntu/ precise main restricteddeb-src http://cn.archive.ubuntu.com/ubuntu/ precise main restricted     ## Major bug fix updates produced after the final release of the  ## distribution.       ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu  ## team. Also, please note that software in universe WILL NOT receive any  ## review or updates from the Ubuntu security team.  deb http://cn.archive.ubuntu.com/ubuntu/ precise universedeb-src http://cn.archive.ubuntu.com/ubuntu/ precise universe     ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu   ## team, and may not be under a free licence. Please satisfy yourself as to   ## your rights to use the software. Also, please note that software in   ## multiverse WILL NOT receive any review or updates from the Ubuntu  ## security team.  deb http://cn.archive.ubuntu.com/ubuntu/ precise multiversedeb-src http://cn.archive.ubuntu.com/ubuntu/ precise multiverse     ## N.B. software from this repository may not have been tested as  ## extensively as that contained in the main release, although it includes  ## newer versions of some applications which may provide useful features.  ## Also, please note that software in backports WILL NOT receive any review  ## or updates from the Ubuntu security team.       deb http://cn.archive.ubuntu.com/ubuntu/ precise-security main restricteddeb-src http://cn.archive.ubuntu.com/ubuntu/ precise-security main restricteddeb http://cn.archive.ubuntu.com/ubuntu/ precise-security universedeb-src http://cn.archive.ubuntu.com/ubuntu/ precise-security universedeb http://cn.archive.ubuntu.com/ubuntu/ precise-security multiversedeb-src http://cn.archive.ubuntu.com/ubuntu/ precise-security multiverse     ## Uncomment the following two lines to add software from Canonical's  ## 'partner' repository.  ## This software is not part of Ubuntu, but is offered by Canonical and the  ## respective vendors as a service to Ubuntu users.  deb http://archive.canonical.com/ubuntu precise partnerdeb-src http://archive.canonical.com/ubuntu precise partner     ## This software is not part of Ubuntu, but is offered by third-party  ## developers who want to ship their latest software.  # deb http://extras.ubuntu.com/ubuntu precise main# deb-src http://extras.ubuntu.com/ubuntu precise main     # codeblock   deb http://ppa.launchpad.net/pasgui/ppa/ubuntu precise maindeb-src http://ppa.launchpad.net/pasgui/ppa/ubuntu precise main     # ubuntu tweak  deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu precise maindeb http://cn.archive.ubuntu.com/ubuntu/ precise-updates restricted main multiverse universedeb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu precise main