Setting up a new PostgreSQL on Redhat systems

Postgres setup turns out to be not as straight forward as I assumed.
When you setup the DB server using yum, the DB comes in a not initialized state, and thus it fails to start using standard service commands.

The below Fedora project wiki link entails a lot of details about this issue:
https://fedoraproject.org/wiki/PostgreSQL

An example on CentOS 7 looks like below.
Once you initialize the DB it starts up with no issues.

[root@vardamir ~]# systemctl start postgresql
Job for postgresql.service failed because the control process exited with error code. See "systemctl status postgresql.service" and "journalctl -xe" for details.
[root@vardamir ~]# journalctl -xe
-- Documentation: http://www.freedesktop.org/wiki/Software/systemd/multiseat
--
-- A new session with the ID 3 has been created for the user root.
--
-- The leading process of the session is 11388.
Sep 19 11:54:29 vardamir systemd[1]: Starting Session 3 of user root.
-- Subject: Unit session-3.scope has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit session-3.scope has begun starting up.
Sep 19 11:54:29 vardamir sshd[11388]: pam_unix(sshd:session): session opened for user root by (uid=0)
Sep 19 11:54:30 vardamir dbus[725]: [system] Activating service name='org.freedesktop.problems' (using servicehelper)
Sep 19 11:54:30 vardamir dbus-daemon[725]: dbus[725]: [system] Activating service name='org.freedesktop.problems' (using servicehelper)
Sep 19 11:54:30 vardamir dbus[725]: [system] Successfully activated service 'org.freedesktop.problems'
Sep 19 11:54:30 vardamir dbus-daemon[725]: dbus[725]: [system] Successfully activated service 'org.freedesktop.problems'
Sep 19 11:54:52 vardamir polkitd[1394]: Registered Authentication Agent for unix-process:11426:31997 (system bus name :1.28 [/usr/bin/pkttyagent --notify-fd 5 --fallback],
Sep 19 11:54:52 vardamir systemd[1]: Starting PostgreSQL database server...
-- Subject: Unit postgresql.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit postgresql.service has begun starting up.
Sep 19 11:54:52 vardamir postgresql-check-db-dir[11431]: "/var/lib/pgsql/data" is missing or empty.
Sep 19 11:54:52 vardamir postgresql-check-db-dir[11431]: Use "postgresql-setup initdb" to initialize the database cluster.
Sep 19 11:54:52 vardamir postgresql-check-db-dir[11431]: See /usr/share/doc/postgresql-9.2.15/README.rpm-dist for more information.
Sep 19 11:54:52 vardamir systemd[1]: postgresql.service: control process exited, code=exited status=1
Sep 19 11:54:52 vardamir systemd[1]: Failed to start PostgreSQL database server.
-- Subject: Unit postgresql.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit postgresql.service has failed.
--
-- The result is failed.
Sep 19 11:54:52 vardamir systemd[1]: Unit postgresql.service entered failed state.
Sep 19 11:54:52 vardamir systemd[1]: postgresql.service failed.
Sep 19 11:54:52 vardamir polkitd[1394]: Unregistered Authentication Agent for unix-process:11426:31997 (system bus name :1.28, object path /org/freedesktop/PolicyKit1/Authe
[root@vardamir ~]# postgresql-setup initdb
Initializing database ... OK

[root@vardamir ~]# systemctl status postgresql
● postgresql.service - PostgreSQL database server
   Loaded: loaded (/usr/lib/systemd/system/postgresql.service; enabled; vendor preset: disabled)
   Active: active (running) since Mon 2016-09-19 11:58:57 EDT; 10s ago
  Process: 11542 ExecStart=/usr/bin/pg_ctl start -D ${PGDATA} -s -o -p ${PGPORT} -w -t 300 (code=exited, status=0/SUCCESS)
  Process: 11537 ExecStartPre=/usr/bin/postgresql-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
 Main PID: 11546 (postgres)
   CGroup: /system.slice/postgresql.service
           ├─11546 /usr/bin/postgres -D /var/lib/pgsql/data -p 5432
           ├─11547 postgres: logger process  
           ├─11549 postgres: checkpointer process  
           ├─11550 postgres: writer process  
           ├─11551 postgres: wal writer process  
           ├─11552 postgres: autovacuum launcher process  
           └─11553 postgres: stats collector process  

Sep 19 11:58:56 vardamir systemd[1]: Starting PostgreSQL database server...
Sep 19 11:58:57 vardamir systemd[1]: Started PostgreSQL database server.
[root@vardamir ~]#

To allow the postgresql server (postmaster) to listen on all interfaces, we need to pieces of config changes, 1 in postgresql.conf and other in pg_hba.conf as below.
in postgresql.conf we need to set :

listen_addresses = '*' 

so that the postmaster server listens on all interfaces.
second we need to add a host entry in pg_hba.conf so that clients are allowed to connect.
this config will depend on network config of the installed DB, an example is shown below:

host    all             all             10.0.0.0/8              md5

md5 is used to allow encrypted password authentication.
Don't forget to allow the Linux firewall to open port 5432 so that external users can access the newly created DB server.

Its always better to create another user than the default postgres user and use that for the DB work remotely.