For those unfamiliar, Chaotic-AUR is a self-described automated building repo for AUR packages; if you're currently using AUR to get some of those latest versions of apps as well as apps unavailable in main repositories, Chaotic-AUR can save you an ocean of package installation time as it is serving pre-compiled AUR packages (some of them, anyway). I never had issues adding it to pacman on other arch-based distros, but I just spent two hours trying to get it functioning in Obarun and I'm happy to report on my journey as well as found solution (if you're only interested in solution, skip over to tl;dr part).

After I performed the steps in Chaotic-AUR home page guide, attempting a package search with pacman resulted in error:

oblive@ Ob66 [1] ~ % sudo pacman -Ss ungoogled
error: chaotic-aur: missing required signature
error: database 'chaotic-aur' is not valid (invalid or corrupted database (PGP signature))

As I attempted to sync the files database, more errors followed:

oblive@ Ob66 [1] ~ % sudo pacman -Fy
error: chaotic-aur: missing required signature
:: Synchronizing package databases...
 obcore is up to date
 obextra is up to date
 obcommunity is up to date
 observice is up to date
 core                                                         948.8 KiB   799 KiB/s 00:01 [# ###################################################] 100%
 extra                                                          9.2 MiB  1688 KiB/s 00:06 [# ###################################################] 100%
 community                                                     24.7 MiB  2.62 MiB/s 00:09 [# ###################################################] 100%
 chaotic-aur                                                   29.1 MiB   886 KiB/s 00:34 [# ###################################################] 100%
error: failed retrieving file 'chaotic-aur.files.sig' from chaotic.pl4ygr0und.de : The requested URL returned error: 404
error: failed to synchronize all databases (failed to retrieve some files)

I shuffled some servers around in /etc/pacman.d/chaotic-mirrorlist, but each of the 4 other mirrors from different countries I tried produced the same 404.

Then I noticed that, tucked away at the end of Recommendations section, their guide says "You must have multilib repository enabled", so I enabled both multilib and obmultilib in /etc/pacman.conf, deleted chaotic-aur files from /var/lib/pacman/sync and ran sudo pacman -Fy again, and again 404.

Looking around to see what else could be found I discovered that all of their mirrors were down at that hour. What a coincidence I thought, and waited for an hour to end, observing the status lines going green as it did. Another attempt -- same error. Hoo-boy.

Ultimately, I scanned /etc/pacman.conf once more to see what differentiated [chaotic-aur] from other repos, realizing that in case of missing signatures, custom package repositories require a SigLevel appendix. It could be set to Optional TrustAll but I find it better to set it to Optional TrustedOnly, as per. As it turns out, enabling those multilib repos seems to be unnecessary.

tl;dr

The way to avoid issues with adding Chaotic-AUR to Obarun is to follow Chaotic-AUR guide, but instead of following the last step as described, adding this to /etc/pacman.conf

[chaotic-aur]
SigLevel = Optional TrustedOnly
Include = /etc/pacman.d/chaotic-mirrorlist

That extra line in the middle makes all the difference.



P.S. In the end (you might have seen this coming) it is just my luck that, having gone through all this to be able to install ungoogled-chromium and get my safe surf on without spending God knows how long compiling it from AUR, I've come to learn that it depends on systemd:

unable to satisfy dependency 'systemd' required by ungoogled-chromium

Oh well.