The apt-Get: package has no installation candidate problem occurs in Ubuntu.

The package has no installation candidate problem occurred during software installation today, for example:

# 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

The solution is as follows:
# Apt-Get update
# Apt-Get upgrade
# Apt-Get install <packagename>

In this way, Apt-Get can be used normally ~

Add a third-party address:

Sudo add-Apt-repository "Deb http://archive.canonical.com/lucid partner"

Sudo apt-Get update