我最近安装了 kubuntu。我可以从 muon 软件中心安装软件。但是当我尝试从终端这样做时，我得到了错误。例如在尝试更新时，我得到：
Err http://archive.canonical.com quantal InRelease
Err http://archive.canonical.com quantal Release.gpg
Unable to connect to archive.canonical.com:http:
Err http://archive.ubuntu.com quantal InRelease
Err http://archive.ubuntu.com quantal Release.gpg
Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.201 80]
Reading package lists... Done
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/quantal/InRelease
W: Failed to fetch http://archive.canonical.com/dists/quantal/InRelease
W: Failed to fetch http://archive.canonical.com/dists/quantal/Release.gpg Unable to connect to archive.canonical.com:http:
W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/quantal/Release.gpg Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.201 80]
W: Some index files failed to download. They have been ignored, or old ones used instead.
同样，当我尝试安装 git-core 时，我得到：
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
git git-man liberror-perl
Suggested packages:
git-daemon-run git-daemon-sysvinit git-doc git-el git-arch git-cvs git-svn
git-email git-gui gitk gitweb
The following NEW packages will be installed:
git git-core git-man liberror-perl
0 upgraded, 4 newly installed, 0 to remove and 0 not upgraded.
Need to get 6,704 kB of archives.
After this operation, 15.4 MB of additional disk space will be used.
Do you want to continue [Y/n]? y
Err http://archive.ubuntu.com/ubuntu/ quantal/main liberror-perl all 0.17-1
Could not connect to archive.ubuntu.com:80 (91.189.92.202). - connect (111: Connection refused) [IP: 91.189.92.202 80]
Err http://archive.ubuntu.com/ubuntu/ quantal/main git-man all 1:1.7.10.4-1ubuntu1
Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.202 80]
Err http://archive.ubuntu.com/ubuntu/ quantal/main git i386 1:1.7.10.4-1ubuntu1
Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.202 80]
Err http://archive.ubuntu.com/ubuntu/ quantal/main git-core all 1:1.7.10.4-1ubuntu1
Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.202 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/libe/liberror-perl/liberror-perl_0.17-1_all.deb Could not connect to archive.ubuntu.com:80 (91.189.92.202). - connect (111: Connection refused) [IP: 91.189.92.202 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/g/git/git-man_1.7.10.4-1ubuntu1_all.deb Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.202 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/g/git/git_1.7.10.4-1ubuntu1_i386.deb Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.202 80]
Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/g/git/git-core_1.7.10.4-1ubuntu1_all.deb Unable to connect to archive.ubuntu.com:http: [IP: 91.189.92.202 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
我该如何处理。如果这很重要，我正在代理服务器后面使用互联网。