Unable to start postgresql service on CentOS 7

Make sure you have installed all packages correctly and updated yum repository sections [base] and [updates] before installation as it mentioned in the guide . We have CentOS 7 with PostgreSQL 9.5 and it works perfectly fine with following steps:

vi /etc/yum.repos.d/CentOS-Base.repo
yum localinstall http://yum.postgresql.org/9.5/redhat/rhel-7-x86_64/pgdg-centos95-9.5-2.noarch.rpm
yum list postgres*
yum install -y postgresql95-server.x86_64 postgresql95-contrib.x86_64 postgresql95-libs.x86_64 
/usr/pgsql-9.5/bin/postgresql95-setup initdb
systemctl enable postgresql-9.5.service
systemctl start postgresql-9.5.service 

and finally, systemctl status postgresql-9.5.service should show you something like this:

postgresql-9.5.service - PostgreSQL 9.5 database server
   Loaded: loaded (/usr/lib/systemd/system/postgresql-9.5.service; enabled)
   Active: active (running) since Fri 2016-02-19 00:01:13 UTC; 6min ago
  Process: 10809 ExecStart=/usr/pgsql-9.5/bin/pg_ctl start -D ${PGDATA} -s -w -t 300 (code=exited, status=0/SUCCESS)
  Process: 10802 ExecStartPre=/usr/pgsql-9.5/bin/postgresql95-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
 Main PID: 10811 (postgres)
   CGroup: /system.slice/postgresql-9.5.service
           ├─10811 /usr/pgsql-9.5/bin/postgres -D /var/lib/pgsql/9.5/data
           ├─10812 postgres: logger process   
           ├─10814 postgres: checkpointer process   
           ├─10815 postgres: writer process   
           ├─10816 postgres: wal writer process   
           ├─10817 postgres: autovacuum launcher process   
           └─10818 postgres: stats collector process 

The most common issue is that the database cluster was not initialized. You can initialize it easily by running the postgresql-XX-setup script with the initdb command, e.g.

sudo /usr/pgsql-11/bin/postgresql-11-setup initdb

Then start the Postgres service, e.g.

sudo systemctl start postgresql-11