List all installed packages
# apt-cache pkgnames
List all installed packages starting with openssh
# apt-cache pkgnames openssh
Show real name of the package and show package description
# apt-cache search openssh
Show package information
# apt-cache show openssh
Show dependencies for specified package, whether they are installed or not
# apt-cache showpkg openssh
Show package’s dependencies
# apt-cache depends openssh
Show any unmet dependencies
# apt-cache unmet