I just made a mistake: I installed PostgreSQL on Mac OSX 10.6.7 and when I wanted to connect to it I did
su postgres, then it asked me for a password and I did
sudo passwd postgres to change the password to something I know.
The problem is, as explained here, this created a Unix user account for postgres and afterwards I had two users on my Mac : me and postgres.
So I deleted the postgres account. Now I cannot connect to postgres because I just cannot
su postgres. How to recreate a "locked" user account postgres that I could use safely (by doing
sudo su postgres as I should have done before) ?
Edit: added version of Mac OS X