sudo cp -p /etc/apt/sources.list /etc/apt/sources.list_backup
gksudo gedit /etc/apt/sources.list
Replace everything with the following lines
To use your local mirror you can add "cc." before archive.ubuntu.com (cc = your country code)
e.g. deb
http://lv.archive.ubuntu.com/ubuntu dapper main restricted universe multiverse
## Add comments (##) in front of any line to remove it from being checked.
## Use the following sources.list at your own risk.
deb
http://archive.ubuntu.com/ubuntu dapper main restricted universe multiverse
deb-src
http://archive.ubuntu.com/ubuntu dapper main restricted universe multiverse
## MAJOR BUG FIX UPDATES produced after the final release
deb
http://archive.ubuntu.com/ubuntu dapper-updates main restricted universe multiverse
deb-src
http://archive.ubuntu.com/ubuntu dapper-updates main restricted universe multiverse
## UBUNTU SECURITY UPDATES
deb
http://security.ubuntu.com/ubuntu dapper-security main restricted universe multiverse
deb-src
http://security.ubuntu.com/ubuntu dapper-security main restricted universe multiverse
## BACKPORTS REPOSITORY (Unsupported. May contain illegal packages. Use at own risk.)
deb
http://archive.ubuntu.com/ubuntu dapper-backports main restricted universe multiverse
deb-src
http://archive.ubuntu.com/ubuntu dapper-backports main restricted universe multiverse
## PLF REPOSITORY (Unsupported. May contain illegal packages. Use at own risk.)
deb
http://packages.freecontrib.org/plf dapper free non-free
deb-src
http://packages.freecontrib.org/plf dapper free non-free
## CANONICAL COMMERCIAL REPOSITORY (Hosted on Canonical servers, not Ubuntu
## servers. RealPlayer10, Opera and more to come.)
deb
http://archive.canonical.com/ubuntu dapper-commercial main
Save the edited file
wget
http://packages.freecontrib.org/ubuntu/plf/12B83718.gpg -O- | sudo apt-key add -
sudo apt-get update
基本上大部分软件都有了