Restoring a 'template1' database in PostgreSQL. (https://wiki.postgresql.org/wiki/Adventures_in_PostgreSQL,_Episode_1)

restore.sql

UPDATE pg_database SET datallowconn = TRUE WHERE datname = 'template0';
\c template0
UPDATE pg_database SET datistemplate = FALSE WHERE datname = 'template1';
DROP DATABASE template1;
CREATE DATABASE template1 WITH TEMPLATE = 'template0';
\c template1
UPDATE pg_database SET datistemplate = TRUE WHERE datname = 'template1';
UPDATE pg_database SET datallowconn = FALSE WHERE datname = 'template0';