If you run into an error like this:

error: ... "Levente Polyak (anthraxx) <levente@leventepolyak.net>" is unknown trust

Try refreshing they keyring for Arch and, if you are using Endeavour, also for Endeavour:

sudo pacman -Sy archlinux-keyring endeavouros-keyring

Then try to run pacman -Syu again. If it still fails, try these:

sudo pacman-key --refresh
sudo pacman-key --populate archlinux artix

If installing still fails with a similar error or you get a GPG error from the pacman-key command you can try to initialise the key-ring.

sudo mv /etc/pacman.d/gnupg /etc/pacman.d/gnupg-backup
sudo pacman-key --init
sudo pacman-key --populate archlinux endeavouros artix       ← only include Endeavour or Artix if applicable
sudo pacman-key --refresh-keys

Then you could try updating/re-installing all the keyrings:

pacman -Ss keyring | grep installed
sudo pacman -Sy archlinux-keyring gnome-keyring endeavouros-keyring artix-keyring... whatever is installed

If you get an error about info@endeavouros not being known then do this:

sudo pacman-key --lsign-key "EndeavourOS"

…then try updating all the keyrings again.

If that still doesn't do the trick and you trust the package and want to ignore the key issue, you can try downloading the package (or leaving it/not deleting it when the key error appears) and then installing it using pacman -U.

References:

1. https://wiki.archlinux.org/title/Pacman#Signature_from_%22User_%3Cemail@example.org%3E%22_is_unknown_trust,_installation_failed
2. https://wiki.archlinux.org/title/Pacman/Package_signing#Resetting_all_the_keys
3. https://forum.endeavouros.com/t/unable-to-install-yay-and-endeavouros-keyring/2035

Problem

# pacman -Sy archlinux-keyring
error: GPGME error: No data
:: Synchronising package databases...
 core     153.9 KiB   325 KiB/s 00:00 [###################] 100%
 extra is up to date
 community is up to date
error: GPGME error: No data
error: failed to synchronize all databases (unexpected error)

Solution: Clear the database cache and rebuild.

mv /var/lib/pacman/sync /var/tmp/
pacman -Syu

If you cannot log-in as root from a terminal prompt, e.g., with EndeavourOS, it is likely due to the shell being wrong.

In EndeavourOS you will see this in /etc/passwd (using, e.g., vipw):

root:x:0:0:root:/root:/usr/bin/bash

While /usr/bin/bash technically points to the same binary as /bin/bash, the PAM pam_nologin.so module will prevent the log-in of any user who does not have a shell that is listed in /etc/shells. If you check /etc/shells you will see that only /bin/bash and not /usr/bin/bash, is listed there.

Change the root entry thus:

root:x:0:0:root:/root:/bin/bash

… and you will be able to log-in as root.