apt-get无法连接
系统：ubuntu 12
我这里用了代理，我已经设置了系统的代理
设置：系统-》网络设置-》
通过浏览器没有问题的，但是apt-get的话，报错，我猜应该是无法连接网络的原因。
问题：
1：按照网上的步骤设置了apt-get，无效。
2：apt-get的代理设置，和系统的代理设置，什么关系？
sgq@sgq-PC-MY18AEZE4:~$ sudo apt-get source time
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: You must put some 'source' URIs in your sources.list
sgq@sgq-PC-MY18AEZE4:~$ cat /etc/apt/sources.list
#deb cdrom:[Ubuntu 12.04 LTS _Precise Pangolin_ - Release i386 (20120423)]/ precise main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ precise main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted
## 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://us.archive.ubuntu.com/ubuntu/ precise universe
deb-src http://us.archive.ubuntu.com/ubuntu/ precise universe
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates universe
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates 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://us.archive.ubuntu.com/ubuntu/ precise multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise multiverse
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates 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://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu precise-security main restricted
deb-src http://security.ubuntu.com/ubuntu precise-security main restricted
deb http://security.ubuntu.com/ubuntu precise-security universe
deb-src http://security.ubuntu.com/ubuntu precise-security universe
deb http://security.ubuntu.com/ubuntu precise-security multiverse
deb-src http://security.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 partner
# deb-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
sgq@sgq-PC-MY18AEZE4:~$ sudo apt-get update
Ign http://extras.ubuntu.com precise InRelease
Err http://extras.ubuntu.com precise Release.gpg
Unable to connect to extras.ubuntu.com:http:
Ign http://extras.ubuntu.com precise Release
Ign http://extras.ubuntu.com precise/main TranslationIndex
Err http://extras.ubuntu.com precise/main Sources
Unable to connect to extras.ubuntu.com:http:
Err http://extras.ubuntu.com precise/main i386 Packages
Unable to connect to extras.ubuntu.com:http:
Err http://extras.ubuntu.com precise/main Translation-en_US
Unable to connect to extras.ubuntu.com:http:
Err http://extras.ubuntu.com precise/main Translation-en
Unable to connect to extras.ubuntu.com:http:
