Yeah.
pactree -r parallel
pacman -Qi parallel | grep Required
And some others depending on how you want things.
Maybe also worth a note … I did a quick install of parallel just to see if that alone would impact pamac … and after doing another build job it did not. So the things are also ‘running’ somehow.
both shows rebuild detector is not required by anyone.
I wonder
pacman -Qi rebuild-detector | grep Reason
But anyhoo … it means its up to you if you want to keep it.
rebuild-detector is a utility that is supposed to tell you when you need to rebuild aur packages.
it says explicitly installed. I cannot come up with other explanation than being part of some command i copypasted to make something work.
At least its technically less mysterious for the ecosystem … even if it is still mysterious on a personal level 
Parallel seems to be a dependency of rebuild-director, which judging by the explicitly installed and the installed date which is the system installation date is part of the default XFCE Iso, at least the May 23 edition which i used to install. Or pulled by calamares on first install.
I’m gonna chalk it up to you installing it on that first day until proved otherwise…
rebuild-detector is not part of the default package list … now … or months back.
And come to think of it … why would it be?
Its sole purpose is warning about AUR packages that need rebuilding.
Maybe it gets pulled automatically when one toggles the aur toggle in pamac settings? That might be something i did on the first day of a fresh install.
This rebuild-detector was proposed for an update in 2021 ; maybe in February or March 
I remember answering a question on the french forum regarding this warning.
[2021-04-18T20:54:04+0200] [ALPM] running 'rebuild-detector.hook'...
[2021-04-18T20:54:05+0200] [ALPM-SCRIPTLET] parallel: Warning: $HOME not set. Using /tmp.
I also have parallel installed as a dependency of rebuild-detector.
philm mentions rebuild-detector in this topic about an update on 2023-06-04, that’s when I installed it:
Continuing the discussion from [Stable Update] 2023-06-04 - Kernels, Gnome 44.1, Plasma 5.27.5, Python 3.11, Toolchain, Firefox:
Which was a suggestion, not a requirement.
rebuild-detector is only needed for the AUR.
And then not a need … lets say ‘desirable’ for people that want something to check for, and nag about, required rebuilding of AUR packages after system updates.
I also understand not expecting an otherwise small and mostly unrelated package to fundamentally change the way parts of my system work, including updates, without any interaction.
parallel lets you run things … in parallel, at the same time.
Why thats needed for the checker I dont know (though I might guess its just to do multiple checks at once or similar)… and how thats supplanting itself to be used during package updates I also dont know.
(see also my above test of simply installing parallel and then building a package - made no difference. Hence parallel has to be running somehow for these things to happen.)
I dont know much about parallel … but I would guess that somewhere in its documentation is how to control it. And there also how to deal with that message one way or another. Or even configure whether parallel is used during the update process.
Of course folks can also just remove rebuild-detector and parallel.
No, it was not to nag about!
I followed his suggestion, I love Philm and Manjaro
I also love his suggestion of checkrebuild, it worked really well!
Also the warning being discussed here is nothing serious I think, I was just curious.
I only meant the purpose of the utility is to “nag” the user about needing to rebuild packages.
I am not sure this is the intended purpose of the utility.
This tool helps you find Arch Linux packages that were built against older versions of dependencies and therefore need to be rebuilt to function properly.
Supported checks:
- ldd: An executable is linked against a non-existent shared library
- python: A package was built against an older Python version
- perl: A package was built against an older Perl version
- ruby: A package was built against an older Ruby version
- haskell: A package was built against an older Haskell version
– GitHub - maximbaz/rebuild-detector: Detects which Arch Linux packages need to be rebuilt
If the purpose is check for changes of custom AUR scripts there is scripts targeting that specific operation.
I mean its any packages … which technically includes repo packages and ‘alien’ packages … but the far more likely/common candidates would be those foreign packages (and would be the only ones the user can do anything about).
The repo packages are supposed to have already been built against the required libraries and a synced system should not have such issues with official packages (unless something goes wrong).
This all changes somewhat for developers … but for users … its roughly above.
That is not the purpose.
The purpose is to detect when a package needs to be rebuilt against current libraries.
(or … when there are ‘issues resolving file dependencies’ … which equates to above)
Just like in your example quote:
What scenario does a user encounter this with repository packages?
And if they do … what can they do about it?
The majority use-case for users is to be notified when a foreign package needs to be rebuilt … which in most cases means ‘when an AUR package needs to be rebuilt’.
I may have been vague in my comment - my apology.
The topic concludes that the warning seen in pamac relates to rebuild-detector.
That application’s purpose appears defined in the github repo - thus I relate to that - and I quoted the purpose from it’s github repo.
In which case the rebuild-detector is not as relevant as other tools which target AUR specifically.
rebuild-detector may provide some similarities and could potentially be useful - but the initial purpose has nothing to do with AUR - at least to my understanding of the source.
The warning comes from parallel which is pulled as a dependency of rebuild-detector.
After some pondering and history checking … users finally realized it was not from pamac, and did not originate from the ISO, or calamares … but was indeed from parallel which was not installed intentionally … but was installed as a dependency when they explicitly installed rebuild-detector (for exactly the use-case described).
The mystery has been solved.
If you say so. I dont use anything of the sort.
But maybe tell @philm … because thats where the original suggestion is from. 
Continuing the discussion from [Stable Update] 2023-06-04 - Kernels, Gnome 44.1, Plasma 5.27.5, Python 3.11, Toolchain, Firefox:
From my logs:
30336 │ [2020-12-31T01:04:50+0100] [PAMAC] synchronizing package lists
30337 │ [2020-12-31T01:04:55+0100] [ALPM] transaction started
30338 │ [2020-12-31T01:04:55+0100] [ALPM] installed rebuild-detector (4.1.5-1)
30339 │ [2020-12-31T01:04:55+0100] [ALPM] transaction completed
30340 │ [2020-12-31T01:04:55+0100] [ALPM] running '30-systemd-update.hook'..
I use parallel in some of my own scripts and never get such warning when running that way. The warning shows up only when I’m running system updates from my terminal.
This thread helped me to wrap my mind around what’s going on here, thanks. The rebuild-detector is simply a tool that “hooks” into pacman, hence the connection between update and those freakin warnings. Although, I still have no clue why parallel complains about $HOME not being set, when run by the hook though. Maybe because it has been called by sudo.
context dear, context
Python 3.10 is the context and checkrebuild is valid in that context.
Some only see the words - and don’t get the meaning - and I didn’t pull custom AUR scripts into the context of rebuild-detector others managed that beautifully.
It says “Anything else” from the AUR…
