The specified username was not found in the pg_shadow system table, meaning the user does not exist. See Chapter 10 for more on adding users.

This database cannot be found because it does not exist. Note that if you do not specify a database name to a PostgreSQL connection, it will attempt to connect to the provided username.

You have succeeded in contacting the server, but the server is not accepting your connection. The server refused the connection because it cannot find an entry for testuser using testdb at their IP address (123.123.123.1) in the pg_hba.conf file.

You have succeeded in contacting the server and it is replying back, but the connection failed password authorization. Check the password you are supplying to the server, and make sure that it is correct. Further, you can check the Kerberos or Ident software programs if you are using them for your password authentication.

You may want to check if this user has a password. If this user does not have one, and the pg_hba.conf file is set to check for passwords, it will still check every user for their password. For all users without a defined password, a NULL password is assigned to that user. When the user tries to log in and does not specify a password, it will compare the NULL password to the NULL input, and it will return false.

On the other hand, if the user tries to supply a password (even a blank one), it will compare that input value with the NULL password and still return false. If you are using password authentication, you must assign a password to all users. If a password is not assigned to a user in such a scheme, password authentication will always fail, and the user will not be able to log in.