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sudo rm /var/lib/pacman/db.lck

The beauty of Linux distros is sometimes they will the explicitly display the solution along with the error message. As you can see in the above output, it says: ".. you can remove /var/lib/pacman/db.lck".

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So, I simply deleted the aforementioned file with command:

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$ sudo rm /var/lib/pacman/db.lck