This tutorial covers:

1. Installing PostgreSQL 16
2. Initializing database clusters using two different methods
3. Starting PostgreSQL using systemctl and pg_ctl

Understanding the Basics

Before we begin the installation, let's understand the key concepts and tools we'll be using.

PostgreSQL Repository (PGDG)

What is a Repository? A repository is a storage location from which your system retrieves and installs software packages. Think of it as an app store for Linux.

Why do we need the PostgreSQL Repository?

• Rocky Linux comes with built-in repositories, but they contain older versions of PostgreSQL
• The official PostgreSQL Global Development Group (PGDG) repository provides the latest versions
• PGDG repository is maintained by the PostgreSQL community
• It ensures you get the most recent features, performance improvements, and security patches

What happens when you install the repository?

sudo dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-9-x86_64/pgdg-redhat-repo-latest.noarch.rpm

This command:

1. Downloads the repository configuration file
2. Installs it to /etc/yum.repos.d/
3. Tells your system where to find PostgreSQL packages
4. Enables access to multiple PostgreSQL versions (12, 13, 14, 15, 16)

Why disable the built-in PostgreSQL module?

sudo dnf -qy module disable postgresql

Rocky Linux 9 has a built-in PostgreSQL module that conflicts with PGDG packages. Disabling it ensures the system uses PGDG versions instead.

systemctl - System Service Manager

What is systemctl?systemctl is the command-line tool for controlling systemd, which is the service manager for modern Linux systems (RHEL 7+, Rocky Linux, Ubuntu 16.04+, etc.).

What does it do?

• Manages services (start, stop, restart)
• Controls auto-start on boot
• Monitors service status
• Manages service dependencies
• Provides centralized logging

Common systemctl commands:

sudo systemctl start postgresql-16      # Start the service now
sudo systemctl stop postgresql-16       # Stop the service now
sudo systemctl restart postgresql-16    # Stop then start
sudo systemctl reload postgresql-16     # Reload config without stopping
sudo systemctl status postgresql-16     # Check if running
sudo systemctl enable postgresql-16     # Auto-start on boot
sudo systemctl disable postgresql-16    # Don't auto-start on boot

Why use systemctl for PostgreSQL?

• Production Standard: Industry best practice
• Automatic Restart: If PostgreSQL crashes, systemd can restart it
• Boot Integration: Starts automatically when server reboots
• Logging: Integrates with journalctl for centralized logs
• Dependencies: Ensures network and other services start first

pg_ctl - PostgreSQL Control Utility

What is pg_ctl?pg_ctl is PostgreSQL's built-in control utility that directly manages the PostgreSQL server process.

What does it do?

• Starts and stops the PostgreSQL server
• Initializes database clusters
• Reloads configuration
• Promotes standbys to primary
• Direct control without systemd

Basic pg_ctl syntax:

/usr/pgsql-16/bin/pg_ctl -D /path/to/data/directory <action>

Common pg_ctl commands:

# Start PostgreSQL
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev start

# Stop PostgreSQL (3 shutdown modes)
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev stop -m smart      # Wait for clients to disconnect
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev stop -m fast       # Disconnect clients gracefully
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev stop -m immediate  # Force shutdown (emergency)

# Restart PostgreSQL
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev restart

# Reload configuration (no restart needed)
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev reload

# Check status
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev status

Shutdown modes explained:

1. Smart mode (-m smart)
   • Waits for all clients to disconnect
   • No new connections accepted
   • Safest but slowest
2. Fast mode (-m fast) - DEFAULT
   • Disconnects all clients immediately
   • Rolls back active transactions
   • Fast and safe
   • Recommended for most situations
3. Immediate mode (-m immediate)
   • Emergency shutdown
   • Kills all processes immediately
   • Requires crash recovery on restart
   • Use only in emergencies

When to use pg_ctl?

• Development: Quick testing without systemd
• Debugging: Direct control for troubleshooting
• Multiple Instances: Running several PostgreSQL clusters on different ports
• Custom setups: Non-default data directories

systemctl vs pg_ctl: Which Should You Use?

initdb - Database Cluster Initialization

What is initdb?initdb creates a new database cluster. A cluster is a collection of databases managed by a single PostgreSQL server instance.

What does initdb create?

1. System Catalogs: Internal tables that track databases, users, tables
2. Template Databases: template0, template1, postgres
3. Configuration Files: postgresql.conf, pg_hba.conf
4. Directory Structure: All necessary subdirectories
5. Initial WAL Files: Write-Ahead Log for transactions

Two ways to run initdb:

1. Via postgresql-16-setup script (wrapper)

   sudo /usr/pgsql-16/bin/postgresql-16-setup initdb
   

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   • Creates cluster in /var/lib/pgsql/16/data
   • Uses default port 5432
   • Automatically configures systemd
2. Via pg_ctl initdb (direct control)

   /usr/pgsql-16/bin/pg_ctl initdb -D /pgDATA/16/sutadev
   

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   • Creates cluster in custom location
   • Can use custom port (e.g., 5433)
   • Requires manual configuration

Tutorial Overview

In this tutorial, you will learn TWO METHODS:

Method 1: Using systemctl (Production Standard)

• Initialize with: postgresql-16-setup initdb
• Data directory: /var/lib/pgsql/16/data
• Port: 5432 (default)
• Start with: systemctl start postgresql-16
• Best for: Production, standard setups

Method 2: Using pg_ctl (Custom Setup)

• Initialize with: pg_ctl initdb -D /pgDATA/16/sutadev
• Data directory: /pgDATA/16/sutadev
• Port: 5433 (custom)
• Start with: pg_ctl -D /pgDATA/16/sutadev start
• Best for: Development, multiple instances, custom requirements

Both methods are independent - you can follow Method 1 only, Method 2 only, or both.

Part 1: Install PostgreSQL Repository

This step is the same for both methods.

# Add PostgreSQL repository
sudo dnf install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-9-x86_64/pgdg-redhat-repo-latest.noarch.rpm

# Disable built-in PostgreSQL module
sudo dnf -qy module disable postgresql

Part 2: Install PostgreSQL Packages

This step is the same for both methods.

# Install PostgreSQL 16.10 (compatible with Rocky Linux 9)
sudo dnf install -y \
  postgresql16-server-16.10-1PGDG.rhel9 \
  postgresql16-16.10-1PGDG.rhel9 \
  postgresql16-contrib-16.10-1PGDG.rhel9

# Verify installation
rpm -qa | grep postgresql16

Method 1: Using systemctl (Default Setup)

This method uses the default PostgreSQL setup with systemd management.

Characteristics:

• Data directory: /var/lib/pgsql/16/data
• Port: 5432
• Service management: systemctl
• Auto-start: Yes (when enabled)

Step 1: Initialize Database Cluster

# Initialize using the setup script
sudo /usr/pgsql-16/bin/postgresql-16-setup initdb

Output:

Initializing database ... OK

This creates the database cluster in /var/lib/pgsql/16/data.

Step 2: Start PostgreSQL with systemctl

# Start PostgreSQL
sudo systemctl start postgresql-16

# Enable auto-start on boot
sudo systemctl enable postgresql-16

# Check status
sudo systemctl status postgresql-16

Expected output:

● postgresql-16.service - PostgreSQL 16 database server
   Loaded: loaded (/usr/lib/systemd/system/postgresql-16.service; enabled)
   Active: active (running)

Step 3: Verify PostgreSQL is Running

# Check if accepting connections
sudo -u postgres /usr/pgsql-16/bin/pg_isready

# Should show: /var/run/postgresql:5432 - accepting connections

Step 4: Connect to PostgreSQL

# Switch to postgres user
sudo su - postgres

# Connect to database
psql

# You should see:
# psql (16.10)
# Type "help" for help.
# postgres=#

Inside psql:

-- Check version
SELECT version();

-- Check port
SHOW port;
-- Should show: 5432

-- Check data directory
SHOW data_directory;
-- Should show: /var/lib/pgsql/16/data

-- Exit
\q

Exit from postgres user:

exit

Method 1 Complete! ✅

You now have PostgreSQL running on:

• Port: 5432
• Data directory: /var/lib/pgsql/16/data
• Management: systemctl

Common systemctl commands:

sudo systemctl start postgresql-16     # Start
sudo systemctl stop postgresql-16      # Stop
sudo systemctl restart postgresql-16   # Restart
sudo systemctl status postgresql-16    # Status
sudo systemctl reload postgresql-16    # Reload config

Method 2: Using pg_ctl (Custom Setup)

This method uses a custom data directory and pg_ctl for management.

Characteristics:

• Data directory: /pgDATA/16/sutadev
• Port: 5433
• Service management: pg_ctl
• Auto-start: No (manual start)

Step 1: Create Parent Directory

# Create parent directory
sudo mkdir -p /pgDATA/16

# Set ownership to postgres user
sudo chown -R postgres:postgres /pgDATA

Step 2: Initialize Database Cluster

# Switch to postgres user
sudo su - postgres

# Initialize cluster in custom location
/usr/pgsql-16/bin/pg_ctl initdb -D /pgDATA/16/sutadev

Output:

The files belonging to this database system will be owned by user "postgres".
...
creating directory /pgDATA/16/sutadev ... ok
creating subdirectories ... ok
...
Success. You can now start the database server using:
    /usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev start

Step 3: Configure Custom Port

Still as postgres user:

# Edit postgresql.conf to use port 5433
sed -i "s/#port = 5432/port = 5433/" /pgDATA/16/sutadev/postgresql.conf

# Verify the change
grep "^port" /pgDATA/16/sutadev/postgresql.conf
# Should show: port = 5433

Step 4: Start PostgreSQL with pg_ctl

# Start PostgreSQL (still as postgres user)
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev start

# Check status
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev status

Output:

pg_ctl: server is running (PID: 12345)
/usr/pgsql-16/bin/postgres "-D" "/pgDATA/16/sutadev"

Step 5: Verify PostgreSQL is Running

# Check if accepting connections (custom port)
/usr/pgsql-16/bin/pg_isready -p 5433

# Should show: /tmp:5433 - accepting connections

Step 6: Connect to PostgreSQL

# Connect to database on custom port
psql -p 5433

# You should see:
# psql (16.10)
# Type "help" for help.
# postgres=#

Inside psql:

-- Check version
SELECT version();

-- Check port
SHOW port;
-- Should show: 5433

-- Check data directory
SHOW data_directory;
-- Should show: /pgDATA/16/sutadev

-- Exit
\q

Exit from postgres user:

exit

Method 2 Complete! ✅

You now have PostgreSQL running on:

• Port: 5433
• Data directory: /pgDATA/16/sutadev
• Management: pg_ctl

Common pg_ctl commands:

# Switch to postgres user first
sudo su - postgres

# Start
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev start

# Stop (fast mode)
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev stop -m fast

# Restart
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev restart

# Status
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev status

# Reload config (no restart)
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev reload

Comparison Summary

Both Methods Running Together

If you completed both methods, you now have TWO PostgreSQL instances running:

# Check both are running
sudo -u postgres /usr/pgsql-16/bin/pg_isready -p 5432  # Method 1
sudo -u postgres /usr/pgsql-16/bin/pg_isready -p 5433  # Method 2

# Connect to Method 1
sudo -u postgres psql -p 5432

# Connect to Method 2
sudo -u postgres psql -p 5433

Important: These are completely independent PostgreSQL instances with separate:

• Data directories
• Configurations
• Ports
• Databases

Quick Reference

Method 1 Commands

# Start/Stop/Restart
sudo systemctl start postgresql-16
sudo systemctl stop postgresql-16
sudo systemctl restart postgresql-16

# Connect
sudo -u postgres psql

Method 2 Commands

# Start/Stop/Restart (as postgres user)
sudo su - postgres
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev start
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev stop
/usr/pgsql-16/bin/pg_ctl -D /pgDATA/16/sutadev restart
exit

# Connect
sudo -u postgres psql -p 5433

Summary

You learned:

✅ Installation: Install PostgreSQL 16 from PGDG repository

✅ Method 1 - systemctl:

• Default location: /var/lib/pgsql/16/data
• Port: 5432
• Managed by systemd
• Best for production

✅ Method 2 - pg_ctl:

• Custom location: /pgDATA/16/sutadev
• Port: 5433
• Manual management
• Best for development/testing

Both methods are valid and serve different purposes!