Sunday, June 14, 2020

Install Postgresql 12 on Linux Mint


Linux mint is a Linux distro based on a popular debian based Linux known as Ubuntu. One reason this Linux is popular, is that it fits on many older computers with lower end hardware specifications, and have support for a wide array of monitors. At the same time, this Linux supports many of the modern hardware drivers.

The current Linux Mint is version 19.3 with the code name "Tricia", is released on 18th December 2019. This is developed from Ubuntu version named Bionic. Among the features that one should know about Tricia includes:

  • It is a long term support (LTS) which means, patches will be maintained till 2023.
  • Installation of Linux Mint have better hardware detection and supports modern BIOS installation to utilise password at BIOS.
  • Include a movie player that utilises hardware optimisation.
  • Its Linux desktop environment called Cinnamon, is light weight enough for many lower spec computer. Computers with lower speed hard disk have always suffered in a windows environment, Cinnamon greatly improves any windows experience.
  • Higher level of security for those who are paranoid about PC security.

Postgresql 12

Among the world's most popular open sourced relational database management system (RDBMS) is Postgresql. Default installation will also create a database called postgres and a user with the same name, postgres. Installation comes with a separate application for the server, and a client. A tool, psql is to manage the server from the command line. There are many other applications that can manage Postgresql with a graphical point and click approach.

Version 12 is released on 3rd October 2019 with the following features:
  • Improved table indexing features. Such as rebuild index table without blocking writes to an index, and this reduces down time.
  • Partitioning of tables to improved queries from a limited set of data.
  • JSON document query support.
  • Just-in-time compilation to process large data (data warehouse) more efficiently.


Linux Mint 19.x by default installs Postgresql version 10. In order to install version 12, Linux Mint must have the latest packages installed to reduce chances of package dependency errors. These are summary of steps in order to install Postgresql version 12.

  1. Add Postgresql repository
  2. Update existing system
  3. Install Postgresql 12 server. This includes the server (postgresql-12) and client (postgresql-client-12) application.
sudo sh -c 'echo "deb bionic-pgdg main" > /etc/apt/sources.list.d/postgresql.list'
wget --quiet -O - | sudo apt-key add -
sudo apt update
sudo apt upgrade

sudo apt install postgresql-12

Once installed, it will prompt

pg_ctlcluster 12 main start

Following are among the files and locations at default install.

  • The database will be stored at /var/lib/postgresql/12/main
  • Logging information at /var/log/postgresql/postgresql-12-main.log
Documentation can be display with the command;

man postgresql

Accessing the server

Default installation includes the user postgres. Access the server using this user.

sudo -u postgres psql

Here are a list of psql commands to get you started.

Once in psql, here are several commands to browse the database;

Display server version (the Uppercase is a matter of good practice)
SELECT version();

List database schema

Switch database schema
\c database_name

Describe a table
\d table_name

Get the last command

Show history of commands

Help with a command
\h command_name

Exit Postgresql client

You can refer to previous posting "Create database and user" to further try the database.

* Install PHP 7.4 notes (not related to postgresql)
sudo apt-get install -y php7.4-{bcmath,bz2,intl,gd,mbstring,pgsql,zip}
sudo apt-get install -y php7.4-{curl,common,xml,xsl}

Friday, June 5, 2020

Install Tensorflow and Keras on Centos 7 Linux

Tensorflow provides a version that utilise the GPU of a server to perform much more heavier computations. Tensorflow version 1.6 onwards are optimimsed to use AVX instructions that is not available in older CPUs.

Centos 7 Linux updated
Installed Python (see previous posting)
Created a project directory called tensorflow

Default steps are to install Tensorflow 2.x (see tensorflow), but server environments that does not support AVX, they need to install Tensorflow 1.5 (see article and blog). To determine if AVX support is available, run the following command and look for AVX or AVX2.

more /proc/cpuinfo | grep flags

My output shows no AVX.
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx lm constant_tsc rep_good nopl eagerfpu pni monitor ssse3 lahf_lm

Configure the project directory for python:

python3 -m venv my_env

Step 1: Install Tensorflow (Or tensorflow-gpu)

cd tensorflow
source my_env/bin/activate

Install Tensorflow application, then print its version

pip install --upgrade tensorflow

Or for server that doesn't have AVX support,

pip install tensorflow==1.15

pip show tensorflow

Step 2: Test Tensorflow install

Create a script file with following contents;

import tensorflow as tf
hello = tf.constant('Hello, World')
session = tf.Session()
print( )

Run the script


Step 3: Install Keras

pip install --upgrade scikit-learn pillow
pip install --upgrade keras keras-utils

Or for server that doesn't have AVX support,

pip install --upgrade scikit-learn pillow
pip install keras==2.1.6

pip show keras

Configuration file will be at ~/.keras/keras.conf
    "floatx": "float32",
    "epsilon": 1e-07,
    "backend": "tensorflow",
    "image_data_format": "channels_last"

Test install by editing

import tensorflow as tf
from tensorflow import keras
hello = tf.constant('Hello, World')
session = tf.Session()
print( )

The above instructions are meant to provide the platform prior to my learning chatbot at site and colab.

Thursday, June 4, 2020

Install Python on Centos 7 Linux

Python is a programming language that can be used for:
  1. Back-end web application
  2. Desktop application
  3. Processing huge amount of data
  4. Control a computer
Example of a basic Python command:

print("Hello, world!")

Install Python

Pip is a tool to manage packages/libraries within Python. On Centos 7, the default pip is version 9.0.3 and it should be upgraded once python is installed.

Following are notes to install Python 3 on Centos 7 Linux. All these are at the command prompt.

sudo yum install python3  python3-devel

Check the installed version

python3 -V

Create directory for python projects

mkdir projects

cd projects

python3 -m venv my_env

Initiate the python project environment

source my_env/bin/activate

Create your first programme in a file called and save the following line.

print("Hello, World")

Run the programme.


Upgrade pip package manager.

pip install --upgrade pip

Once done with Python, leave the project environment.


Extra pip example 

Install setuptools to install applications from source

pip install --upgrade setuptools wheel

Install Tensorflow application, then print its version

pip install --upgrade tensorflow
pip show tensorflow

Saturday, May 16, 2020

Postgresql 10: Create database and user

Postgresql provides creation of database schemas with a specific role or user assigned to it. This is great where there will be a few users who need to access one or another database on the same server.

Default user created by Postgresql is named postgres, that can be used to create any database schema and user roles. For this tutorial, Postgresql is installed on Centos Linux 7. To start postgresql client and access the default user, at the terminal type;
sudo -u postgres psql

Steps to create the database are as follows;
  1. Create the database. In this case we call it student_management.
  2. Create user and assign password for login. We call out user student and password is 123456
  3. Assign the access to the database. We give full privileges to read, write.
  4. Enable the user to login.
  5. Exit from client (optional)
CREATE DATABASE student_management;
GRANT ALL PRIVILEGES ON DATABASE student_management TO student;

Next, test by login with that user account and password.

There is an alternative approach for a dedicated database server that require users to have their own databases. This approach doesn't require you to use the psql client. It is useful when you plan to have scripts that auto generate the process.

sudo -u postgres createdb developer
sudo -u postgres createuser --interactive
sudo adduser developer
sudo passwd developer

The user "developer" can login and get connected to the default database with the same name as the user. In this case the database name is "developer".

Login as the user.
sudo -i -u developer psql

Friday, May 15, 2020

Laravel: Getting started

Notes on getting started with Laravel, on Centos Linux 6,7,8.

In order to get started with Laravel, there are required software to run composer and laravel that needs to be installed. This includes;
  1. Web server
  2. PHP
  3. Composer
  4. Node JS

Step 1. Install PHP 7.3 or newer.

If you havent installed PHP, follow notes from previous post.
After installing PHP, install all the regular extensions. Ensure PHP is working with the web browser.
sudo yum install php-cli php-zip wget unzip  php-dom php-posix php-shmop  php-xsl php-xmlrender

Step 2. Web server.

In this case, I am using Apache HTTPD. Install this and test that the php is working.
sudo yum install httpd

Step 3. Composer

Download the installer.
php -r "copy('', 'composer-setup.php');
sudo php composer-setup.php --install-dir=/usr/local/bin --filename=composer

Step 4. Node JS

sudo yum install nodejs

You are ready to work with Laravel projects. Here are links to the remainder tutorials
Part 1, Part 2,

Thursday, May 14, 2020

Install Postgresql 10 database on Centos 7

Installation and configuration of Postgresql 10 on Centos 7


Centos Linux 7 by default installs Postgresql version 9. These are summary of steps in order to install Postgresql version 10, the following steps can be taken.
  1. Yum manages the installation of software, and utilises a list of repositories of there to locate its repository. It is highly advised to update existing software with yum before proceeding with software installations. Add the additional repository site must be added for Postgresql 10 from
  2. Install the version of Postgresql database client software that is needed to open the database.
  3. Install the version of Postgresql database server software. This will hold the database files and controlling software.
  4. Initialise Postgresql database files. This will create the username "postgres" where it is configured to run all the client commands.
  5. Start Postgresql database server.
  6. Test the server by requesting info.
  7. Configure Centos 7 to automatically start at boot up.

At a terminal, execute the commands

# yum install
# yum install postgresql10
# yum install postgresql10-server
# /usr/pgsql-10/bin/postgresql-10-setup initdb
# systemctl start postgresql-10
# /usr/pgsql-10/bin/postgres -V
# systemctl enable postgresql-10

Using the client

For those who wish to use the postgres clients, here are commands to get started.

Login as user "postgres" and use the Postgresql client.

# sudo -u postgres psql

Once in psql, here are several commands to browse the database;

Display server version (the Uppercase is a matter of good practice)
SELECT version();

List database schema

Switch database schema
\c database_name

Describe a table
\d table_name

Get the last command

Show history of commands

Help with a command
\h command_name

Exit Postgresql client

Remote access and firewall

In development databases, many users may require to access the database from remote computers. On the default Centos 7, with firewall running this require some configuration. The steps involved;

  1. Add httpd and postgresql service rule to the firewall. The httpd is an additional web service I am demonstrating here.
  2. Restart firewall
  3. Configure postgresql to listen from incoming networks, or all networks. Replace the line listen_addresses = 'localhost'
  4. Allow user authentication from incoming networks, or all networks. Replace the line with
  5. Restart postgresql
At a terminal, execute the commands

# sudo firewall-cmd --add-port=8080/tcp --permanent
# sudo firewall-cmd --add-service=postgresql --permanent
# sudo firewall-cmd --reload
# sudo vi /var/lib/pgsql/10/data/postgresql.conf

listen_addresses = '*'

# sudo vi /var/lib/pgsql/10/data/pg_hba.conf

host    all             all               md5

# sudo systemctl restart postgresql-10

Tuesday, May 5, 2020

Laravel 6 Step by Step Tutorial Part 2

Laravel 6 provides an advanced framework for programmers to quickly create enterprise on a wide number of PHP platforms. Part 2 of this Laravel guide can be found at Laravel 6 Part 2

In order to proceed with part 2 of the tutorial, please complete part 1 as posted in
First of Laravel 6 step by step guide.

The tutorial can be followed by having your copy of PHP 7.3 onwards and a database. Notes are provided for MySQL and Postgresql database.

This demonstrates how to implement data relationships of has one. In Laravel this is implemented with the function belongsTo. The idea is to maintain a list of articles where each have one author. That author could essentially have written many articles.

Saturday, January 18, 2020

Install MongoDB database on Centos 7

MongoDB is a noSQL database and is available on Centos Linux 7. Ensure that SElinux is only on permissive.

For cases SElinux is enforcing, additional steps need to be taken which is outside of this installation note.

Step 1: Configure the repository

Create the file /etc/yum.repos.d/mongodb-org.repo

name=MongoDB Repository

Step 2: Install and start

sudo yum install -y mongodb-org
sudo systemctl start mongod

If all is running good, then allow it to start at boot time.

sudo systemctl enable mongod

Step 3: Verify


Further configuration can be done with the file /etc/mongod.conf

Allow database through the firewall

sudo firewall-cmd --zone=public --add-port=27017/tcp --permanent
sudo firewall-cmd --reload

Those with Selinux in mode Enforcing, allow the default mongodb port.

sudo semanage port -a -t mongod_port_t -p tcp 27017

Friday, January 17, 2020

Install Mariadb database on Centos 7

MariaDB is a replacement for Oracle Mysql Community edition.

Installation on Centos 7 is as follows;

Step 1: Install

sudo yum install mariadb-server mariadb

Step 2: Configure and assign database root password

sudo systemctl start mariadb
sudo mysql_secure_installation

sudo systemctl enable mariadb

Step 3: Verify

mysql -u root -p

Configuration of the database can be done with the files at

To allow access of the database through the firewall.

sudo firewall-cmd --permanent --add-service=mysql

Howto install PHP 7 on Centos 7

The Centos Linux 7 comes with php version 5.4.16. It is possible to install php version 7 by adding an additional rpm repository. Lets see how its done to install php 7.3 (which is the version I have chosen).

Step 1: Add Remi repository for php 7.3

sudo yum install yum-utils
sudo yum install epel-release
sudo yum install
sudo yum-config-manager --enable remi-php73

Step 2: Install php

sudo yum install php php-common php-opcache php-mcrypt php-cli php-gd php-curl php-json php-mysql php-mbstring

Step 3: Verify 

php --version

For the web server to accept php, it needs to be restarted.

Specialised development environment will require additional php extensions. For example laravel framework could require;

opcache, bz2, calendar, ctype, curl, dom, exif, fileinfo, ftp, gd, gettext, iconv, mysqlnd, pdo, phar, posix, shmop, simpleexml, sockets, sqlite3, sysvmsg, sysvsem, sysvshm, tokenizer, xml, xmlwriter, xsl, mcrypt, mysqli, pdo_mysqli, wddx, xmlrender, zip.

and the list continues.

Wednesday, January 15, 2020

Android Studio 3 Installation on MS Windows 10

Android Studio is provided by Google for development of Android applications. Android Studio or AS is available for MS Windows, Linux and Mac OSX.

Following are steps to get started with a fresh MS Windows 10 machine.

Step 1. Download Android Studio

Download from

and follow the installation process.

Step 2. Install Android Studio

Double click and run the downloaded EXE file. Accept the default selections and click "Next" until its installed. An internet connection is required to complete the installation.

Once installation is done, create a first application and test the emulator. In this example, I have choosen min API 23. You will be prompted by MS Windows to allow OpenJDK through firewall. Allow and proceed. Have to consider, the emulator require 1.5Gb additional disk space.

Step 3. Start and create an emulator.

In Android Studio, click "Tools" ->"AVD Manager" ->"Create Virtual Device"

Select "Phone", "Pixel 2". Click "Clone Device". This allows us to keep the original configuration intact and change what ever is required. Click Next.

Click Download for "Nougat" with API 25. Read and Accept the agreements. Click "Next" then "Finish"

Friday, January 10, 2020

First of Laravel 6 step by step tutorial

Just completed the first part of the step by step tutorial.

Feel free to check it out at

This will complement the Laravel notes found on this blog.

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