The command that is used to update the list of available packages when using dpkg based package management is apt-get update12. The apt-get command is a high-level tool that works with dpkg and provides a user-friendly interface for managing packages3. The apt-get update command is used to synchronize the package index files from the sources specified in the /etc/apt/sources.list file12. This command does not install or upgrade any packages, but only downloads the information about the latest versions and dependencies of the packages12. The apt-get update command is usually run before the apt-get upgrade or apt-get install commands, which are used to upgrade or install packages respectively12.

The other options in the question are not correct because:

B. apt-get upgrade: This command is used to upgrade the installed packages to the latest versions, not to update the list of available packages12.

C. apt-cache update: There is no such command in Linux. The apt-cache command is used to query and display information about the packages, not to update them4.

D. apt-get refresh: There is no such command in Linux. The closest command is apt-get update, which is the correct answer.

E. apt-cache upgrade: There is no such command in Linux. The closest command is apt-get upgrade, which is not the correct answer.

References:

1: How To Manage Packages Using apt-get, apt-cache, apt-file and dpkg Commands In Debian Based Systems 2: Ubuntu Manpage: apt-get - APT package handling utility – command-line interface 3: dpkg - Debian Wiki 4: Ubuntu Manpage: apt-cache - query the APT cache