How to deal with FATAL: role "admin0" does not exist and PG :: ConnectionBad: FATAL: role "admin0" does not exist when executing rails db: create

I will write a summary of the solution for latecomers about the solution when an error occurs when executing rails db: create.

Execution environment

windows 10 home ubuntu 20.04 LTS ruby 2.7.1 Rails 6.0.3 postgresql 11

Error statement

$ rails db:create
FATAL:  role "admin0" does not exist
Couldn't create 'taskleaf2_development' database. Please check your configuration.
rails aborted!
PG::ConnectionBad: FATAL:  role "admin0" does not exist
/home/admin0/taskleaf2/bin/rails:9:in `<top (required)>'
/home/admin0/taskleaf2/bin/spring:15:in `<top (required)>'
bin/rails:3:in `load'
bin/rails:3:in `<main>'
Tasks: TOP => db:create
(See full trace by running task with --trace)

Is the key point this time around the 5th line from the top?

Error resolution order

I had encountered a similar error before and had already resolved it, so I tried the same method. https://teratail.com/questions/297341

$ yarn install

However, even this could not be solved.

Notice that the error is PG :: ConnectionBad :. However, the DB should be running like the following command ...?

$ sudo service postgresql start
[sudo]admin0 password:
 * Starting PostgreSQL 11 database server　[ OK ]
 * Starting PostgreSQL 13 database server ［ OK ]

I decided to try starting it by another means (below).

$ sudo su - postgres
 \q

When I ran rails db: create again, the error statement changed.

$ rails db:create
WARNING:  could not flush dirty data: Function not implemented
Created database 'taskleaf2_development'
WARNING:  could not flush dirty data: Function not implemented
Created database 'taskleaf2_test'

After that, I searched with this error sentence https://stackoverflow.com/questions/45437824/postgresql-warning-could-not-flush-dirty-data-function-not-implemented Because this seemed to be influential Part of the contents of /etc/postgresql/11/main/postgresql.conf was rewritten as follows

fsync = off
data_sync_retry = true

Try running rails db: create again

rails db:create
Database 'taskleaf2_development' already exists
Database 'taskleaf2_test' already exists

Apparently it was successful. Since the server was able to start, it is judged that this solved the problem this time.