How to start PgSQL (Postgres) server

Try directly using:

sudo /etc/init.d/postgresql start

otherwise try:

pgrep -u postgres -fa -- -D

More info:
How to start Postgres
There again are several ways to start Postgres. If you’re running a Debian-based distribution, you should find the perl wrappers pretty handy.

For Debian or Debian-based (including Ubuntu) Linux distributions
First, issue pg_lsclusters to find out your cluster name:

pg_lsclusters

Ver Cluster Port Status Owner Data directory Log file
12 main 5432 online postgres /var/lib/postgresql/12/main /var/log/postgresql/postgresql-12-main.log

To start that particular cluster, you just need to issue:

pg_ctlcluster <Version> <Name> start

So, in our example, it will be:

pg_ctlcluster 12 main start

if that gives an error, use:

sudo /etc/init.d/postgresql start

You may need to then run:

584 rake db:drop
586 rake db:create
587 rake db:migrate
588 rake db:seed