Linux: Minor Annoyances and How To Fix Them

A work in progress.

Arch: Invalid or corrupted database (PGP signature)

First, change the SigLevel in pacman.conf:

sudoedit /etc/pacman.conf  
# SigLevel = Required DatabaseOptional
SigLevel = Optional TrustAll  

If that doesn't fix it, try clearing your pacman cache:

sudo pacman -Sc  

And try again. If you still get the error, you probably have a package that is actually corrupted. This is very rare in the main repos. If it is from the AUR, contact the package mantainer.