install yum repository for CentOS7.x

# yum install https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7-x86_64/pgdg-centos96-9.6-3.noarch.rpm
Loaded plugins: fastestmirror, langpacks
pgdg-centos96-9.6-3.noarch.rpm                                                                                                                         | 4.7 kB  00:00:00     
Examining /var/tmp/yum-root-H7b1MM/pgdg-centos96-9.6-3.noarch.rpm: pgdg-centos96-9.6-3.noarch
Marking /var/tmp/yum-root-H7b1MM/pgdg-centos96-9.6-3.noarch.rpm to be installed
Resolving Dependencies
--> Running transaction check
---> Package pgdg-centos96.noarch 0:9.6-3 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

==============================================================================================================================================================================
 Package                                   Arch                               Version                           Repository                                               Size
==============================================================================================================================================================================
Installing:
 pgdg-centos96                             noarch                             9.6-3                             /pgdg-centos96-9.6-3.noarch                             2.7 k

Transaction Summary
==============================================================================================================================================================================
Install  1 Package

Total size: 2.7 k
Installed size: 2.7 k
Is this ok [y/d/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : pgdg-centos96-9.6-3.noarch                                                                                                                                 1/1 
  Verifying  : pgdg-centos96-9.6-3.noarch                                                                                                                                 1/1 

Installed:
  pgdg-centos96.noarch 0:9.6-3                                                                                                                                                

Complete!

install postgresql96

# yum install postgresql96 postgresql96-contrib postgresql96-devel postgresql96-libs postgresql96-server
Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base: ftp.jaist.ac.jp
 * elrepo: ftp.yz.yamagata-u.ac.jp
 * epel: ftp.jaist.ac.jp
 * epel-debuginfo: ftp.jaist.ac.jp
 * epel-source: ftp.jaist.ac.jp
 * extras: ftp.jaist.ac.jp
 * updates: ftp.jaist.ac.jp
Resolving Dependencies
--> Running transaction check
---> Package postgresql96.x86_64 0:9.6.11-1PGDG.rhel7 will be installed
---> Package postgresql96-contrib.x86_64 0:9.6.11-1PGDG.rhel7 will be installed
---> Package postgresql96-devel.x86_64 0:9.6.11-1PGDG.rhel7 will be installed
---> Package postgresql96-libs.x86_64 0:9.6.11-1PGDG.rhel7 will be installed
---> Package postgresql96-server.x86_64 0:9.6.11-1PGDG.rhel7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

==============================================================================================================================================================================
 Package                                          Arch                               Version                                         Repository                          Size
==============================================================================================================================================================================
Installing:
 postgresql96                                     x86_64                             9.6.11-1PGDG.rhel7                              pgdg96                             1.4 M
 postgresql96-contrib                             x86_64                             9.6.11-1PGDG.rhel7                              pgdg96                             569 k
 postgresql96-devel                               x86_64                             9.6.11-1PGDG.rhel7                              pgdg96                             1.8 M
 postgresql96-libs                                x86_64                             9.6.11-1PGDG.rhel7                              pgdg96                             318 k
 postgresql96-server                              x86_64                             9.6.11-1PGDG.rhel7                              pgdg96                             4.5 M

Transaction Summary
==============================================================================================================================================================================
Install  5 Packages

Total download size: 8.6 M
Installed size: 38 M
Is this ok [y/d/N]: y
Downloading packages:
(1/5): postgresql96-contrib-9.6.11-1PGDG.rhel7.x86_64.rpm                                                                                              | 569 kB  00:00:02     
(2/5): postgresql96-9.6.11-1PGDG.rhel7.x86_64.rpm                                                                                                      | 1.4 MB  00:00:02     
(3/5): postgresql96-libs-9.6.11-1PGDG.rhel7.x86_64.rpm                                                                                                 | 318 kB  00:00:00     
(4/5): postgresql96-devel-9.6.11-1PGDG.rhel7.x86_64.rpm                                                                                                | 1.8 MB  00:00:00     
(5/5): postgresql96-server-9.6.11-1PGDG.rhel7.x86_64.rpm                                                                                               | 4.5 MB  00:00:00     
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                         3.0 MB/s | 8.6 MB  00:00:02     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : postgresql96-libs-9.6.11-1PGDG.rhel7.x86_64                                                                                                                1/5 
  Installing : postgresql96-9.6.11-1PGDG.rhel7.x86_64                                                                                                                     2/5 
  Installing : postgresql96-server-9.6.11-1PGDG.rhel7.x86_64                                                                                                              3/5 
  Installing : postgresql96-devel-9.6.11-1PGDG.rhel7.x86_64                                                                                                               4/5 
  Installing : postgresql96-contrib-9.6.11-1PGDG.rhel7.x86_64                                                                                                             5/5 
  Verifying  : postgresql96-libs-9.6.11-1PGDG.rhel7.x86_64                                                                                                                1/5 
  Verifying  : postgresql96-server-9.6.11-1PGDG.rhel7.x86_64                                                                                                              2/5 
  Verifying  : postgresql96-9.6.11-1PGDG.rhel7.x86_64                                                                                                                     3/5 
  Verifying  : postgresql96-devel-9.6.11-1PGDG.rhel7.x86_64                                                                                                               4/5 
  Verifying  : postgresql96-contrib-9.6.11-1PGDG.rhel7.x86_64                                                                                                             5/5 

Installed:
  postgresql96.x86_64 0:9.6.11-1PGDG.rhel7                postgresql96-contrib.x86_64 0:9.6.11-1PGDG.rhel7           postgresql96-devel.x86_64 0:9.6.11-1PGDG.rhel7          
  postgresql96-libs.x86_64 0:9.6.11-1PGDG.rhel7           postgresql96-server.x86_64 0:9.6.11-1PGDG.rhel7           

Complete!

check postgres account id

# cat /etc/passwd
postgres:x:26:26:PostgreSQL Server:/var/lib/pgsql:/bin/bash

start and check its status

# systemctl start postgresql-9.6.service
 
# systemctl status postgresql-9.6.service 
● postgresql-9.6.service - PostgreSQL 9.6 database server
   Loaded: loaded (/usr/lib/systemd/system/postgresql-9.6.service; disabled; vendor preset: disabled)
   Active: active (running) since Wed 2018-11-28 13:26:25 JST; 6s ago
     Docs: https://www.postgresql.org/docs/9.6/static/
  Process: 10937 ExecStartPre=/usr/pgsql-9.6/bin/postgresql96-check-db-dir ${PGDATA} (code=exited, status=0/SUCCESS)
 Main PID: 10943 (postmaster)
    Tasks: 7
   CGroup: /system.slice/postgresql-9.6.service
           ├─10943 /usr/pgsql-9.6/bin/postmaster -D /var/lib/pgsql/9.6/data/
           ├─10946 postgres: logger process   
           ├─10948 postgres: checkpointer process   
           ├─10949 postgres: writer process   
           ├─10950 postgres: wal writer process   
           ├─10951 postgres: autovacuum launcher process   
           └─10952 postgres: stats collector process