How to diagnose and fix the 28P01 invalid_password error code in Postgres.

The 28P01 error code in PostgreSQL corresponds to an “invalid_password” error, indicating that authentication has failed due to an incorrect password being supplied for a user account when attempting to connect to the database.

To diagnose and fix the 28P01 error, consider the following steps:

  1. Verify the Password: Ensure that the password being used is correct. Passwords in PostgreSQL are case-sensitive, so check for any inadvertent case changes or typos.
  2. Check Password Encryption: PostgreSQL supports different password encryption methods. Ensure that the client is using the same method expected by the server. For example, if the server is set up to use md5 password encryption, the client must also supply an md5-encrypted password.
  3. Review pg_hba.conf: The pg_hba.conf file controls client authentication in PostgreSQL. Verify that the authentication method specified for the user, host, and database combination is correct and that the user is allowed to connect from the current location.

Here are some examples of how the 28P01 error might occur and how to resolve it:

  • Example 1: Incorrect Password Input If you’re using psql to connect to the database and receive the 28P01 error, the first step is to ensure you’re entering the correct password:
  psql -U username -d database_name -h host -W

After running this command, you’ll be prompted for a password. Double-check that you’re entering the correct password for the user.

  • Example 2: Resetting a Forgotten Password If the password has been forgotten, it can be reset by a superuser or the account owner with the following SQL command:
  ALTER USER username WITH PASSWORD 'new_password';

Remember to replace username with the actual username and new_password with the new password. If you’re not the superuser, you’ll need their assistance to reset the password.

  • Example 3: Updating pg_hba.conf Authentication Method If the pg_hba.conf file is set to use a different authentication method than the client expects, you might encounter the 28P01 error. For example, if pg_hba.conf is set to peer authentication for local connections, but you’re supplying a password, authentication will fail. To fix this, you might need to change the method to md5 or another appropriate method:
  # TYPE  DATABASE        USER            ADDRESS                 METHOD
  local   all             all                                     md5

After modifying pg_hba.conf, you must reload the PostgreSQL configuration for the changes to take effect:

  pg_ctl reload

or you can also use the SQL command:

  SELECT pg_reload_conf();
  • Example 4: Password Encryption Method Mismatch If the server expects a password encrypted with scram-sha-256 but the client provides an md5-encrypted password, authentication will fail. Ensure that both the server and client are configured to use the same password encryption method. You can set the password encryption method in the postgresql.conf file:
  password_encryption = scram-sha-256

After changing the password encryption method, you will need to update the user’s password to use the new encryption:

  ALTER USER username WITH PASSWORD 'new_password';

Keep in mind that after changing the pg_hba.conf or postgresql.conf files, you should always reload the PostgreSQL service to apply the changes. Also, when resetting passwords or changing configuration files, it’s crucial to maintain secure practices to protect your database.

For further information on authentication methods and user management in PostgreSQL, you can refer to the official PostgreSQL documentation. Understanding the authentication process and configuration will help you resolve issues related to the 28P01 error code more effectively.

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