> the distri installer does not modify files, it only ever adds images to the package store The set of installed packages also comprises state of the system. I

> the distri installer does not modify files, it only ever adds images to the package store The set of installed packages also comprises state of the system. It's the same as in OOP: modification of data in objects is equivalent to a function accepting prior state and outputting an updated state—only it's more difficult to track the changes when they're done from the inside and/or in a far-reaching manner of OOP. So, in this example, known changes on the installer's level would encompass the installed/updated packages, leaving determining file-level changes to setup scripts of each package. I guess different strategies may exist, but pretty sure this is approximately what other package managers do. > if you don’t update your Debian machine for a few weeks and want to install a new package, maybe that requires a libc update, which requires service restarts, etc. Afaik, if you don't restart services, you can run into incompatibilities between old and updated libraries at the runtime of a service. Suppose I'm running a web server in e.g. Python, and I happen to call a script for the first time after such an update. The script loads an extension which relies on freshly updated libc (for example), while the server has the old one loaded. In short, the system also has state in memory, which after an update differs from the state on the disk—and using mismatching parts of those two is not advisable. I'm not even sure what would happen in C-level libs in this case (“symbol missing” probably?), but I guess everyone lived through mismatched parts of code at the level of scripting languages, and the result is usually an exception. If you catch this situation at the update time, you can gracefully restart the web server while handing new requests to the newly-started instance. If you bump into it at the run time, that's an error for at least one client.