Ubuntu 出現apt-get: Package has no installation candidate問題

今天在安裝軟件的時候出現了Package has no installation candidate的問題，如：

#  apt-get install <packagename>
Reading package lists... Done
Building dependency tree... Done
Package aptitude is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package <packagename> has no installation candidate

解決方法以下：
# apt-get update
# apt-get upgrade
# apt-get install <packagename>

這樣就能夠正常使用apt-get了～

添加第三方地址：

sudo add-apt-repository "deb http://archive.canonical.com/ lucid partner"

sudo apt-get update