DEPENDENCIES

If you’re a Windows or MacOS user, the idea of dependencies is probably a foreign one. Windows and MacOS have a pretty much fixed runtime that all apps comply with. Apps on these platforms know what system libraries, services and interpreters are available because everybody has the same set provided in the OS. There are exceptions (like apps that require that you to install Python or older Visual Basic runtimes, for example), but in general, apps require nothing else to be installed beforehand.

Linux is not like that. Application libraries, services and toolsets aren’t built-in or assumed universal. For example, a media player app might require a library that decodes H.264 compressed video. You have to install both the library and the app. Many Linux apps have dozens of such dependencies (which is why we have Linux distributions that bundle the most common libraries and include package managers), and it can become a little nightmarish to manage them all, especially when you have things like version conflicts. This is why Docker and similar systems like LXC have become popular, since they bundle both the app and all its dependencies into a single package that requires nothing else.