Docker not recognizing Postgresql data directory

you're changing default postgresql data path hence you need to initialize the database. try this

volumes:
    - ./init.sql:/docker-entrypoint-initdb.d/init.sql

here is the init.sql file

CREATE USER docker;
CREATE DATABASE docker;
GRANT ALL PRIVILEGES ON DATABASE docker TO docker;

I had the same issue, I restarted Docker daemon and even restarted the machine, but didn't fix the issue.
The path /var/lib/postgresql/data was not even on the FS.

Note: Performing a docker ps was not showing the postgresql container as running.

Solution (docker-compose):

• Close postgres container:
  docker-compose -f <path_to_my_docker_compose_file.yaml> down postgres

• Start postgres container:
  docker-compose -f <path_to_my_docker_compose_file.yaml> -d up postgres

-- That did the trick! --

Solution (docker):

docker stop <postgres_container>
docker start <postgres_container>

Another solution that you can try:
initdb <temporary_volum_folder>
Example:
initdb /tmp/postgres
docker-compose -f <path_to_my_docker_compose_file.yaml> -d up postgres
or
initdb /tmp/postgres docker start <postgres_container>

Note:
In my case the postgres image is defined in docker-compose.yaml file, and it can be observed I don't define PG_DAT nor PG_VERSION and the container runs ok.

  postgres:
    image: postgres:9.6.14
    container_name: postgres
    environment:
      POSTGRES_USER: 'pg12345678'
      POSTGRES_PASSWORD: 'pg12345678'
    ports:
      - "5432:5432"

So when have postgres:/var/lib/postgresql/data, it's going to mount /var/lib/postgresql/data to a docker data volume called postgres. Docker data volumes are all stored together in a location that varies depending on the OS.

Try changing it to ./postgres to have it create a directory called postgres relative to your working directory.

Since the source is changing it will recreate the database, and I'd be willing to be fix the error your seeing. If not, it could be a permission issue on the host os.

If you want to tell the PostgreSQL container to make its data persistent, you should:

• Declare the volume at the end of the compose.yaml file

• Declare it external

• Use its name before ":" in the low-level volumes declaration in the PostgreSQL service

• create the external volume by a docker command before containers creation. The name must be the same as in yaml file

That data will persist after Docker or computer restart.

In the PostgreSQL service:

volumes:
  - db_volume:/var/lib/postgresql/data

At the end of the yaml file:

volumes:
  db_volume:
    external: true

The docker command to be run only once, before the container is created for the first time. The volume is persistent:

docker volume create db_volume

-----

_{If you use the real folder path before ":" in the low-level volumes declaration in the postgres service, you will have problems with rights - postgres won't have the necessary rights to work with its own data. I haven't seen a working way to set these rights.}

_{On the other hand, we don't need to know exactly where PostgreSQL stores its data; persistence is enough.}