bash: ifconfig: command not found debian centos ubuntu rhel

This article will be helpful for Ubuntu, CentOS, RHEL, Debian, Raspbian OS users.

ifconfig is a very commonly used command to find the ipaddress of a linux machine. Sometimes we may get an error like

bash: ifconfig: command not found

The reason for this can be because of one of the following reasons.

  • The ifconfig command is not available in the system.
    • In case of this issue, we have to install the net-tools package
  • The ifconfig script is not available in the PATH
    • In this case, we have to try executing /sbin/ifconfig command

In these cases, we can get the ip address details by using another command. We don’t have to install any additional package for issuing the following command

ip addr

If the net-tools package is missing in the system, we can enable ifconfig by installing the package. The command to install the package is given below.

For Ubuntu, Raspbian, Debian OS use the following command

sudo apt-get install net-tools

For RHEL / CentOS users, use the following command

sudo yum install net-tools

Now try ifconfig in the commandline and you will be able to see the ip address details.


How to install Chromium browser in Raspberry Pi debian ?

By default, there will not be any browser included in the debian OS for raspberry Pi. Chromium is one of the best browser for raspberry pi. We can install chromium browser in raspberry pi debian OS using the following simple steps,

sudo apt-get update
sudo apt-get install chromium-browser

Now after doing this, check the home icon in raspberry pi and you will be able to see an additional option “Internet” and on expanding, you can see chromium browser. All set 🙂

Simple Python Program to get the system status of a raspberry Pi

The following program helps you to monitor the status of a raspberry pi. The common parameters that we monitor are CPU, Memory & Disk. This program can be used to get the info of any operating system. This is not limited to raspberry pi.

Here I am providing a simple program that provides the details of all these three parameters. You can enhance this program further and make it part of your application.

Covid-19 patient monitoring using Raspberry Pi

Image Source: CBC Canada

A team from the University of Toronto has created a new way for health-care workers to monitor COVID-19 patients — without having to set foot in their hospital rooms.

The university got a call from Mount Sinai hospital with a requirement to figure out a way to monitor vital signs both continuously and remotely.

The students developed a raspberry pi based continuous remote monitoring system for monitoring the status of the patients without the direct intervention of the nurses.

They attached a standard fingertip probe, already in use in hospitals to monitor vital signs, to a “very, very small computer about the size of a credit card,”

That simple computer, called a Raspberry Pi, can then connect to the internet — allowing health-care workers to check on patients from any nursing station computer, or on their smartphone.

The concept is very simple, the finger clip monitors the respiratory status of the COVID-19 patients. The clip detects the light absorbed by the patient’s blood. The colour vary depending upon the oxygen level in the blood and this is the key factor to monitor. This data will be captured from the finger clip by the Raspberry pi and it gets transmitted to the devices in the nursing station.

The prototype was successful based on several trial deployments made in the Mount Sinai hospital.


University of Toronto supports COVID-19 patient monitoring with Raspberry Pi



Realtime Temperature Monitoring System using Raspberry Pi

Realtime temperature sensing is one of the common requirement. There are a lot of digital thermometers and temperature monitoring devices available in online shopping sites. But most of them just monitors and displays the realtime values. It does not have any intelligence.  The one we are going to build is a smart temperature monitoring system. This system can be used for monitoring atmospheric temperature as well as liquid temperature.

The following blog post explains the set up of a digital temperature monitoring system.

Digital Temperature Monitoring System

We will enhance the above system by adding analytical capability. So that we can analyse and show the temperature trends. The block diagram below shows the high level architecture of the system.


As shown in the above diagram, the system has three blocks.

  • Edge Device & Sensor (Raspberry Pi & Sensor)
  • Data Storage Server
  • Dashboards for the end user

The following are the software components required for this project

  • MQTT for sending the data from the edge to the server.
  • PostgreSQL for storing the data in the server.
  • Python based backend
  • HTML Web UI

I am not going to explain the working of MQTT in this blog post. This was already explained in one of my earlier posts.

Before we start implementing the solution, lets summarize the story line.

  • The requirement is to perform realtime temperature monitoring and analyse the trends & patterns using the historic data.
  • A temperature sensor is attached to a Raspberry Pi which acts as the edge device.
  • Need provision to support multiple edge devices.
  • Capability to monitor the temperature from anywhere

Bird’s eye view of the system

Here we have considered multiple edge devices and also considered the provision of web and mobile application.


Data Model Design

In the PostgreSQL database, we need two base tables for storing the data. We will be able to store data from multiple edge devices located at different locations using this data model. This is a very basic data model. We can enhance this based on our requirement.

  • device_info – This has the metadata of the edge devices. This includes the location details of the device. The column names are given below
    • device_id, device_name, location
  • temperature_data – We store the temperature data from each of the edge devices in this tables. The column names are given below.
    • device_id, timestamp, value

Now let us start developing the application from the edge device. We will modify the program to send the messages to an MQTT topic with the timestamp. The temperature readings will be sent to the server once in every minute. The message format will be as follows. We will be using epoch timestamp in seconds and temperature in Degree Celsius.

{"device_id":"xxx", "timestamp":1584284353, "value": 27.01}

Now lets develop a small python program that send this values to the MQTT topic. For this, we need an MQTT broker to be up and accessible from the Raspberry Pi

Here my central server is a CentOS 7 server and I will be using mosquitto MQTT. The installation steps are explained very detailed in this blog post.

In the central server, these messages will be collected and stored in the database tables.

A sample view of the temperature_data table is shown below.

device_id timestamp value
device_01 1587825234 27
device_02 1587825234 28
device_03 1587825234 23
device_04 1587825234 28
device_05 1587825234 30
device_06 1587825234 26
device_07 1587825234 22
device_08 1587825234 28
device_09 1587825234 32
device_10 1587825234 29
device_11 1587825234 31

Now from this table, we can query and get the required information based on the user requirement. We can either develop custom visualization using javascript or we can query the DB using workbenches or we can even connect & visualize data using visualization tools like Apache Superset, PowerBI etc.


With this I have explained the highlevel architecture and implementation of a sample IoT system. This system can be scaled further by using a proper time series database instead of the Postgres DB.

VPN installation in Raspberry Pi

What is a VPN ?

VPN stands for Virtual Private Network. VPN extends the private network to external networks so that the users can securely interact with the systems within the private network. I will write another post with the complete details of VPN. We will be concentrating on the installation of VPN in raspberry pi in this post.

VPN is a very important requirement for every enterprises. Now a days even individual started using VPN. It is very easy to configure a VPN. Most of the large enterprises use paid VPN services. There are so many VPN service providers available in the market.

This post is about setting up a free VPN service. This can be used in small or medium scale businesses or for your personal purpose as well. I am using this VPN service from the past several years and it worked very well without any issues.

Installation of VPN in raspberry Pi


I have used raspberry Pi for the installation of OpenVpn. The simplest way to install and configure VPN is raspberry Pi is using Pi-VPN. PiVPN supports two VPN backends

  • OpenVPN
  • WireGuard

While doing the installation, it asks for the user to select the preference and it installs accordingly. OpenVPN can be operated in TCP and UDP. I have used both of these protocols. From my personal experience, the best performing and stable one is UDP.

The only advantage with TCP is that we can run Open VPN in TCP port 443 and it bypasses almost all firewalls in external network. The TCP port 443 is globally open for HTTPS. So we can easily access the VPN using the same port. In this way we will not have to request for additional exceptions in the firewall to enable the VPN access.

WireGuard is a new VPN protocol. It uses a completely new protocol as compared to Open VPN. It is fast and secure. This is under development. Currently if you look at the installations, the majority share goes to Open VPN. This is mainly because it was there in the industry from several years and it already proved its capability. WireGuard will be up in the market soon.

More details about the configuration of PiVPN is described in the following URLs.

  1. PiVPN installation
  2. Additional Reference

Integration with Network

The integration is very easy. In two steps we can integrate the VPN.

  • Connect the raspberry Pi to your network using an ethernet cable
  • Create a rule in your firewall or router to allow the traffic from outside to the raspberry Pi through a NAT rule. (Create a port forwarding rule to route the requests from outside to the raspberry Pi connected to the internal network.)

Raspberry Pi 3 released.

Raspberry Pi 3 got released this week. Still remembering the moment before 3 years, my colleague introduced me about this magic device. Then I googled about this device and read the details. I am using this device from the past one year . I have used Raspberry Pi B+, Pi2 and now waiting for the delivery of Pi3 from element14. It is one of the superb devices that I have ever used. I can use my electronics knowledge and computer science knowledge using this. Now the Pi3 came with builtin wifi and bluetooth module so that it can be connected to a wifi or a bluetooth device without any external peripheral. Physical appearance is same as that of Pi2, but this version is more powerful. Now we can say Good Bye..!!! to wifi adapter modules. This will be a very big hit in the IoT market. Expecting more wonders from element14. 🙂

Booting Raspberry Pi2 for the first time

Today I and my colleagues were trying to install Raspbian OS on Raspberry Pi 2 B version. The steps that we followed are explained below.
Before explaining the steps, I am listing down the hardware and softwares that we used.

  • Raspberry Pi2 B version
  • NOOBS 1.4.1 Offline and Network Installer (Release date 2015-05-11).
  • Transcent 16 GB Class 10 memory card
  • Raspberry Pi charger (We used a 5Volt 2A charger)
  • Memory Card Reader.
  • SD Formatter (
  • Windows Laptop
  • Monitor
  • HDMI Cable

We used the steps mentioned in the raspberry pi website for reference. There is an excellent video that explains each and every step for the setup.

The steps we followed are listed below.

  • Inserted the memory card into the Card reader and plugged into the windows machine.
  • Formatted the memory card using the SD Formatter with “FORMAT SIZE ADJUSTMENT” set to “ON”.
  • Copied the NOOBS offline installer zip file to the formatted memory card and extracted it.
  • Unplugged the card reader and put the memory card into the Pi2.
  • Supplied power to the Pi2 which is connected to the monitor using HDMI Cable
  • The Pi2 booted up. We have to select the OS to be installed.
  • Select one OS. Now the OS will be installed and your pi will be ready to use.

We faced an issue while performing the installation. The Pi2 was not booting up. Finally after some struggle, we figured out the issue. We used a phone instead of a memory card reader for connecting the memory card to the computer for formatting. Because of this, the Pi was not booting. We figured out this issue from the status of the ACT LED (Green LED). The green LED should blink in case of normal operation. If the green LED is not blinking, means the Pi is not reading the SD card. In our case the green LED was not blinking. So we started investigating and reviewing the steps that we followed for the SD card set up and finally we found the culprit… Our Mobile Phone . So my suggestion is to use a card reader. Never use any camera or mobile phone instead of card reader. This may unnecessarily waste your time and you will not get any clue of the error also.