backtrack5 r3 中 "enable universe component"

1. 安装 software-center

$ apt-get install software-center

2. 然后
For older versions of ubuntu, there are several options:
    Main Menu: System > Administration > Software Sources.
    Synaptic : System > Administration > Synaptic Package Manager : >> Settings >> Repositories.
    Main Menu: Ubuntu Software Center : >> Edit, Software Sources.

3. 选择 "universe" -->"Close" --> "Reload"

参考: https://help.ubuntu.com/community/Repositories/Ubuntu