Setting postgres user's password when running initdb

--pwfile=filename Makes initdb read the database superuser's password from a file. The first line of the file is taken as the password.

I'm understanding the documentation as saying that the password that I place in the first line of the file (/etc/pgsql/9.2/postgres.password) in my case will be set as the password of the user identified by --username (in my case the postgres user). In this example the postgres user should end up with a password of pass123

If I modify my pg_hba.conf file as follows:

local   all             all                                     peer

and then restart postgres I can get in to the mydb1 Database, selecting from pg_catalog.pg_shadow seems to show that the postgres user doesn't have a password set at all:

mydb1=# select u.* from pg_catalog.pg_shadow u;
 usename  | usesysid | usecreatedb | usesuper | usecatupd | userepl | passwd | valuntil | useconfig
----------+----------+-------------+----------+-----------+---------+--------+----------+-----------
 postgres |       10 | t           | t        | t         | t       |        |          |
(1 row)

This makes me think I've misunderstood the documentation with regard to --pwfile?

Grateful for any advice here.

Cheers,

Edd