Look on my works, ye Mighty, and despair!

I was trying to create a new postgres user, and kept getting the dreaded:

psql: FATAL:  Peer authentication failed for user "fred"

despite the fact I’d added the user to the pg_hba.conf file. It turns out that you need to specify the host:

psql -U fred -h localhost

as well as the user, to get psql to use md5 auth rather than peer.