You just need to do apt-get install --only-upgrade <packagename>. This will upgrade only that single package, and only if it is installed.

If you wish to install the package if it doesn't exist, or upgrade it if it does, you may leave out --only-upgrade.

The goal of fpm is to make it easy and quick to build packages such as rpms, debs, OSX packages, etc.

fpm, as a project, exists to help you build packages, therefore:

• If fpm is not helping you make packages easily, then there is a bug in fpm.
• If you are having a bad time with fpm, then there is a bug in fpm.
• If the documentation is confusing, then this is a bug in fpm.