Imho there’s a difference between “people abuse it” and “it is possible for programs to use software that they shouldn’t even find”. Anyway I noticed just now you weren’t the one to actually ask the initial question of whether it’s technically possible, so I apologize for not noticing this earlier. However I think it’s a meaningless endeavor to ponder whether or not it’s possible when that fact is irrelevant.
It’s not that it’s hard to do. It’s that it goes directly against the idea of NixOS since it breaks the separation. With NixOS I can start a shell in a different iteration of my system without switching over the whole system. If I had all my software installed into standard places, that shell might find things it’s not supposed to find.
Bottom line is: Most things work on NixOS out of the box. The PATH variable is adjusted accordingly to what a program is supposed to find, which in my opinion is perfectly reasonable and enough for software to find other software. The dynamic library paths are hardcoded as absolute paths, so software can find it’s libraries. There’s a special dynamic loader for binaries that don’t adhere to this. And if you really need an FHS compliant environment NixOS gives you the tools to create one in a sandbox.
You can either have the perks of NixOS or use an FHS compliant distro. That’s your choice.
Conflict resolution was not my point. Rather the question which the “most recent” between two almost identical installations…
Choosing the most recent one might be impossible if you have multiple installations of the same package with same version but different features enabled during the configure step.
Nix installs derivations into separate folders. A derivation can be a package, but can also be other things like configuration files, scripts or sources for packages. Nix doesn’t distinguish between these derivations by a name but rather by a hash created from their build instructions.
For example two instances of the same package with a different version are two different derivations and thus nix can have both package versions installed without them interfering with each other. But this goes beyond just a package version. It is e.g. possible to have the same package with the same version but different patches applied, or relying on different versions of dependencies. Since their build instructions differ both can be installed simultaneously.
This approach grants a variety of advantages. For example upgrading your NixOS system just installs new derivations of packages and configuration files that have changed, while keeping previous derivations until they’re garbage collected at a later time. This allows you to switch freely between both iterations of your system, for example if an update causes issues you can just revert back to before an update easily. Another advantage is that an unprivileged user can install packages they need without interfering with the rest of the system, for example an older python version or a newer one, or some software they want but the system does not provide.
The price of having this kind of isolation between packages is that nixos cannot install binaries and libraries into common locations. Effectively /usr/bin only contains the env binary. If you’re familiar with shell scripting you might have run into lines such as . This env util will essentially search bash in your PATH variable and start it. Lines like however will not work, because there’s no bash installed in that location.
Another case where a missing fhs is a problem is when using pre-compiled binaries. In contrast to binaries built through nix, which have their required libraries hardcoded as absolute paths, pre-compiled binaries you download usually only contain the name of the library they need, which works in a conventional fhs environment, because these libraries tend to be found in /libor /usr/lib. On NixOS neither of those are present. There two solutions to this. Either you create an fhs environment by listing the set of derivations to be symlinked into a chroot environment which mimics an FHS. Or you can install https://github.com/Mic92/nix-ld which automatically finds the required libraries the nix way if you start such a binary. There’s also steam-run which installs an fhs with most of the dependencies necessary to start Linux games from Steam.
My system is configured that way (by me) and I regularly use sudo -s.
I just want to see if there’s a root shell and not rely on some hidden timeout 🙄