Your default postgres user is named like your linux user. That default user has limited access privileges, which can cause issues such as:
Doing these things without a superuser will show a Postgres error or (in Ruby) raise PG::InsufficientPrivilege
.
To do so, the application's PostgreSQL user must be a superuser. Grant superuser rights like this:
$ sudo -u postgres psql
# ALTER USER <your username> WITH SUPERUSER;