Postgresql Cluster Creation

initdb Utility Introduction

Database Cluster :
A cluster of databases under one instance of a database server in operation is called a database cluster. A Postgres database, intended to serve as the default database for use by users, utilities, and outside programs, will be present in a database cluster following initialization.

PostgreSQL is a command-line tool used to initialize a new PostgreSQL database cluster. It's typically one of the first steps in setting up a PostgreSQL database system. When you install PostgreSQL, it doesn't automatically create a database for you; instead, it provides you with this utility to create a new database cluster.

A cluster is defined by the port number. The default DB cluster in postgres loaction is “/var/lib/pgsql/13/data”.

Here we can see all the configuration files and parameters. 
    -bash-4.2$ cd /var/lib/pgsql/13/data
    -bash-4.2$ ls -lrt
    total 76
    -rw-------. 1 postgres postgres    88 Nov 14 11:48 postgresql.auto.conf
    drwx------. 2 postgres postgres    18 Nov 14 11:48 pg_xact
    -rw-------. 1 postgres postgres     3 Nov 14 11:48 PG_VERSION
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_twophase
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_tblspc
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_snapshots
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_serial
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_notify
    drwx------. 4 postgres postgres    36 Nov 14 11:48 pg_multixact
    -rw-------. 1 postgres postgres  1636 Nov 14 11:48 pg_ident.conf
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_dynshmem
    drwx------. 2 postgres postgres     6 Nov 14 11:48 pg_commit_ts
    -rw-------. 1 postgres postgres  4631 Nov 15 10:30 pg_hba.conf
    drwx------. 6 postgres postgres    54 Nov 15 10:39 base
    -rw-------. 1 postgres postgres     0 Nov 15 10:39 tablespace_map.old
    drwx------. 2 postgres postgres     6 Nov 15 10:39 pg_replslot
    -rw-------. 1 postgres postgres   224 Nov 15 10:39 backup_label.old
    -rw-------. 1 postgres postgres 28165 Nov 15 10:55 postgresql.conf
    drwx------. 2 postgres postgres    18 Nov 15 10:55 pg_subtrans
    drwx------. 2 postgres postgres     6 Nov 15 10:55 pg_stat
    drwx------. 3 postgres postgres  4096 Nov 15 11:05 pg_wal
    -rw-r--r--. 1 postgres postgres     0 Nov 15 12:43 backup.sql
    drwx------. 2 postgres postgres  4096 Nov 16 10:32 global
    drwx------. 2 postgres postgres  4096 Nov 20 09:41 log
    -rw-------. 1 postgres postgres    30 Nov 23 10:10 current_logfiles
    -rw-------. 1 postgres postgres    58 Nov 23 10:10 postmaster.opts
    drwx------. 4 postgres postgres    68 Nov 23 10:10 pg_logical
    -rw-------. 1 postgres postgres    95 Nov 23 10:10 postmaster.pid
    drwx------. 2 postgres postgres    25 Nov 23 12:02 pg_stat_tmp
Steps to create a Database Cluster :
Step 1 : cd /var/lib/pgsql

Step 2 : Create a folder where the db is to be initiated

Step 3 : The owner and group of the created folder should be postgres and also the folder should have full access. 
  -bash-4.2$ cd /var/lib/pgsql
  -bash-4.2$ mkdir tesdb
  -bash-4.2$ ls -lrt
  total 4
  drwxr-xr-x. 2 postgres postgres    6 Aug 22 10:14 perl5
  drwxr-xr-x. 7 root     root     4096 Aug 31 15:27 pgbadger-11.6
  drwx------. 2 postgres postgres    6 Nov 14 10:46 tbs
  drwx------. 4 postgres postgres   51 Nov 14 11:48 13
  drwxr-xr-x. 2 postgres postgres    6 Nov 23 12:18 tesdb
Step 4 : cd /usr/pgsql-13/bin

Step 5 : ./initdb -D /var/lib/pgsql/tesdb
In the above step we are initialising the db by mentioning the location of the directory we created 
  -bash-4.2$ cd /usr/pgsql-13/bin
  -bash-4.2$  ./initdb -D /var/lib/pgsql/tesdb
  The files belonging to this database system will be owned by user "postgres".
  This user must also own the server process.

  The database cluster will be initialized with locale "en_US.UTF-8".
  The default database encoding has accordingly been set to "UTF8".
  The default text search configuration will be set to "english".

  Data page checksums are disabled.

  fixing permissions on existing directory /var/lib/pgsql/tesdb ... ok
  creating subdirectories ... ok
  selecting dynamic shared memory implementation ... posix
  selecting default max_connections ... 100
  selecting default shared_buffers ... 128MB
  selecting default time zone ... Asia/Kolkata
  creating configuration files ... ok
  running bootstrap script ... ok
  performing post-bootstrap initialization ... ok
  syncing data to disk ... ok

  initdb: warning: enabling "trust" authentication for local connections
  You can change this by editing pg_hba.conf or using the option -A, or
  --auth-local and --auth-host, the next time you run initdb.

  Success. You can now start the database server using:


(Postgresql - Creating cluster using initdb)