FATAL: password authentication failed for user "postgres" (postgresql 11 with pgAdmin 4)

For Windows variant - I too experienced this nasty bug because of pgAdmin for my Windows x64 install of version 9.2. It left my production paralyzed.

In folder C:\Program Files\PostgreSQL\9.2\data or C:\Program Files (x86)\PostgreSQL\9.x\data, you'll find the pg_hba.conf text file.

Find the following lines:

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5

and change METHOD md5 to "trust" like this:

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# IPv4 local connections:
host    all             all             127.0.0.1/32            trust
# IPv6 local connections:
host    all             all             ::1/128                 trust

From Windows>Run type "services.msc" and enter find the right PostgreSQL instance and restart it.

Your DB security is now blown wide open! Heed the warning to return it back to md5 after changing the user password expiry time to say year 2099 for all the relevant users.

You could access your pgpass.conf via pgAdmin -> Files -> open pgpass.conf

That will give you the path of pgpass.conf at the bottom of the window (official documentation).

If you then open this file and edit it to your liking.

If that doesn't work, you can:

• Find your pg_hba.conf, usually in C:\Program Files\PostgreSQL\9.1\data\pg_hba.conf
• If necessary, set the permissions on it so that you can modify it; your user account might not be able to do so until you use the security tab in the properties dialog to give yourself that right by using an admin override.
• Alternately, find notepad / notepad++ in your start menu, right click, choose "Run as administrator", then use File->Open to open pg_hba.conf that way.
• Edit it to set the "host" line for user "postgres" on host "127.0.0.1/32" to "trust". You can add the line if it isn't there; just insert:

host all postgres 127.0.0.1/32 trust

before any other lines. (You can ignore comments, lines beginning with #).

• Restart the PostgreSQL service from the Services control panel (start->run->services.msc)

• connect using psql or pgAdmin4 or whatever you prefer

• and run ALTER USER postgres PASSWORD 'fooBarEatsBarFoodBareFoot'
• remove the line you added to pg_hba.conf or change it back
• restart PostgreSQL again.

Note: CREATE USER is the same as CREATE ROLE except that it implies LOGIN.

$ psql postgres
postgres=# create user postgres with superuser password 'postgres';