Today I have upgraded my Arch Linux, everything was good, and the system was upgraded, but then suddenly pacman refuses to update databases.

This is the error:

When entering this command:

sudo pacman -Sy

The output was:

:: Synchronizing package databases...
error: failed to update core (unexpected error)
error: failed to update extra (unexpected error)
error: failed to update community (unexpected error)
error: failed to synchronize any databases

After looking for the solution I realized that all the mirrors in

/etc/pacman.d/mirrorlist

were commented, so there were not mirrors available to update from.

The simple solution was to uncomment some of them and all was working again.