On Archlinux it is not recommended to update only one package with the package manager pacman. Let’s say I have 11 packages, and one of them is extra/firefox (true story). Updating only a pacman -S firefox could introduce problems, but installing a new single package if it wasn’t there is okay.
So my question is, could we get around this by removing and installing the same package again in one go: pacman -Rs firefox && pacman -S firefox
I think you are a little confused at the problem here. The issue is that partial updates are not supported. The reason for this is very simple, Arch ensures that any given package list works on its own, but not that packages from different versions of the package list work together. So if Firefox depends on libssl the new Firefox package may depend on a new libssl function. If you install that version of Firefox without updating libssl it will cause problems.
There is no way around this limitation. If you install that new Firefox without he new libssl you will have problems. No matter how you try to rules lawyer it. Now 99% of the time this works. Typically packages don’t depend on new library functions right away. But sometimes they do, and that is why as a rule this is unsupported. You are welcome to try it, but if it breaks don’t complain to the devs, they never promised it would work. But this isn’t some policy where you can find a loophole. It is a technical limitation. If you manage to find a loophole people aren’t going to say “oh, that should work, let’s fix it” it will break and you will be on your own to fix it.
Focusing on your commands. The thing is that
pacman -S firefoxis always fine on its own. If Firefox is already installed it will do nothing, if it isn’t it will install the version from the current package list. Both of those operations are supported. Alsopacman -Rs firefox && pacman -S firefoxis really no different than justpacman -S firefox(other than potentially causing problems if the package can’t be allowed to be removed due to dependencies). So your command isn’t accomplishing anything even if it did somehow magically work around the rules.What is really the problem is
pacman -Sy. This command updates the package list without actually updating any packages. This will enter you system into a precarious state where any new package installed or updated (example ourpacman -S firefoxcommand form earlier) will be a version that is mismatched with the rest of your system. This is unsupported and will occasionally cause problems. Generally speaking you shouldn’t runpacman -Sy, any time you are using-Syyou should also be passing-u. This ensures that the package list and your installed packages are updated together.This is an excellent answer and I wish I knew all of this when starting to use archlinux. “Arch does not support partial upgrades” is something you can read everywhere, but it’s rare to find such a good explanation of what exactly a partial upgrade is, and which commands lead to it.
I only learned about all of this when I got into some broken state by randomly running pacman commands.
Everyone, be like this guy. This guy explains stuff well. Newbies need stuff explained.
I’m not familiar with arch or pacman. What prevents a package from becoming too new? Like if a new version of libssl is released that removes a necessary function but a package like Firefox has become abandoned, then even updating everything will result in a broken application. Does it not have version dependencies like debs and rpms?
Adding on to what the other commenter mentioned, that is called a breaking change and would generally be avoided at all costs by libssl. See, e.g., the decades-long python3 transition.
I’m also not familiar. But my understanding is that the package maintainers should prevent this situation. Because otherwise even if there are package version dependencies (I don’t actually know if pacman does this) it would just block the update which results in a partial update which isn’t supported. For example if your theoretical unmaintained Firefox blocks the update of libssl but Python requires new functionality you would be stuck in dependency hell. Leaving this problem to the users just makes this problem worse. So the package maintainers need to sort something out.
It is a huge pain when it happens but tends to be pretty rare in practice. Typically they can just wait for software to update or ship a small patch to fix it. But in the worst case you need to maintain two versions of the common dependency. In lots of distros very common dependencies tend to get different packages for different major version for this reason. For example libfoo1 and libfoo2. Then there can be a period where both are supported while packages slowly move from one to the other.
If a package manager can block an upgrade due to version dependencies, it can also pull in those dependencies for a partial upgrade.
If a function is removed from libssl and it’s used in firefox, firefox build would fail, so it’s still not possible to have a functional setup.
Yeah, that kind of a condition would require the maintainer to patch the source of the non-updated program.
And that would be fine if there is just a little change, with an alternate function available but if the change requires changing the logic of the application, you are essentially expecting the package maintainer to do the software developer’s work.
The deprecation process is a good way to prevent this.
But I’m not doing
pacman -Sy package. That is not what I am talking about. I am only talking aboutpacman -S package, which is not updating the system partially. IF the package depends on something else to update, then the system would need to be updated. But that is not what I was asking, because I only talk about the package with-S package. I just chosefirefoxas an example, it could have been any other package.To make it clear, when I say
-S firefox, then I mean really that without updating a dependency like libssl. The idea is to install only new packages without updating anything on the system. I guess as you say it depends on the dependencies of the package, if this is feasible.But that is my point. Just running
pacman -S firefoxis fine as long as you didn’t runpacman -Syat some point earlier. It won’t update anything, even dependencies. It will just install the version that matches your current package list and system including the right version of any dependencies if they aren’t already installed.But that means if you already have Firefox installed it will do nothing.
We can install a new package if it wasn’t installed with
pacman -S firefox. That is not a partial upgrade of the system. Right? What i don’t understand is, when I uninstall withpacman -Rs firefox, delete the cached firefox package (only that file), then the system is in the same state as before I installed it. Then-S firefoxshould be okay, right? And it even looks up the new version. This is my question, if that would work correctly.IF no dependency tries to update too. Off course in that case I would stop. Without
pacman -Sy, I never do that anyway, only-Syu.To add to the other comment, package managers keep a local copy of the list of available packages and the version. When you do a
pacman -S xxxthe package manager looks up xxx in the cache and downloads the package from whatever mirror youre using as well as any dependencies, looking them up in the same way from your cache. This works for a while even if theres a new update available because mirrors usually keep a few previous versions.Once you do a
pacman -Syyou update your cache to the latest one. If you then update xxx, it will update xxx and pull in any dependency updates required, but any other packages that depended on the same packages dont get updated, leaving you in a partially upgraded state.That’s all you need to know. As long as you always use
pacman -Syuyou will be fine.pacman -Syis the real problem. The wiki page is pretty clear about the sequences of commands that are problematic https://wiki.archlinux.org/title/System_maintenance#Partial_upgrades_are_unsupported.This isn’t correct. It won’t look up the new version. Assuming that the system was in a consistent state it will download the exact same package that you deleted. The system only ever “updates” when you run
pacman -Sy. Until you use-yall packages are effectively pinned at a specific version. If the version that gets installed is different than the one you removed it probably means that you were breaking the partial update rule previously.