The start of the PostgreSQL server

When the Postgres server is not started, the Psql command will error:

psql: unable to connect to server: no file or directory
     Whether the server is running locally and is in a Unix domain socket
     Ready to accept connections on "/var/run/postgresql/.s.PGSQL.5432"?

Workaround:

by command

/etc/init.d/postgresql start

Start the Postgres server.

Receive information

[OK] Starting PostgreSQL (via Systemctl): Postgresql.service.

Indicates a successful start.

And then through

sudo su -postgres

Switch to User Postgres.

Use the Psql command under the Postgres user to enter the database operation.

Other:

To stop the Postgres server:

Restart the Postgres server:

/etc/init.d/postgresql restart

The start of the PostgreSQL server