Articles written by Parakh Singhal

Git Rebase vs. Merge


Every version control system offers a core set of functionalities, of which, the ability to create branches and then merge changes into branches are offered by both central and distributed version control systems. The way different systems behave is different and hence, often, while the result will be the merging of changes, the way it accomplished and the resulting history created are different.

Consider the following scenario:
You have created a feature branch from a long-running branch. Someone in the team commits in changes into the parent long-running branch and you have to bring in the changes into the feature child branch that you are using for active development. There are two ways to do that in Git:
1.    Merge command
2.    Rebase command

Both the commands achieve the same outcome of integrating the changes from parent long-running branch into the feature child branch. Where things differ, is the resulting commit history that gets created due to the usage of the commands.

Merge command

In the aforementioned scenario, if you use the merge command, the resulting commit history will bear a merge commit. Note that the merge command does not alter the history of your feature branch in any way. On the contrary, the merge commit provides a context for the changes bought from the parent branch.
Run the following commands in bash shell to simulate a merge in git to bring in changes from a parent branch to a child branch:

$ mkdir Merge
$ cd Merge
$ git init
$ touch file.txt
$ printf “First instalment of work done in master branch” > file.txt
$ git add .
$ git commit “First commit in master branch” 
$ git branch dev
$ git checkout dev
$ printf “\n\nWork done in dev branch” >> file.txt
$ git commit -am “First commit in dev branch”
$ git status
$ git checkout master
$ printf “\n\n\n\nSecond instalment of work done in master branch” >> file.txt
$ git commit -am “Second commit in master branch”
$ git checkout dev
$ git merge master
Resolve conflicts, if any. Perform a git commit which is going to be a merge commit.
$ git log –oneline –graph

The result will be something like shown in the image below:


Log history after a merge. Notice the merge commit made in the end

Figure 1 Log history after a merge. Notice the merge commit made in the end

Rebase command

Rebase command, as the name suggests re-creates the base for the child branch while bringing in the changes from the parent branch. This results in a cleaner, unidirectional history, but the context under which the changes were bought in, gets lost. It appears that the child feature branch always worked with the changes bought from the parent long-running since the beginning of its creation.

Run the following commands in bash shell to simulate a rebase in git to bring in changes from a parent branch to a child branch:

$ mkdir Rebase
$ cd Rebase
$ git init
$ touch file.txt
$ printf “Work done in master branch” > file.txt
$ git add .
$ git commit -m “First commit in master branch”
$ git branch dev
$ git checkout dev
$ printf “\n\nWork done in dev branch” >> file.txt
$ git commit -am “First commit in dev branch”
$ git checkout master
$ printf “\n\n\n\nSecond instalment of work done in master branch” >> file.txt
$ git commit -am “Second commit in master branch”
$ git checkout dev
$ git rebase master
Resolve conflicts, if any. Perform a git add . followed by git rebase –continue
$ git log –oneline –graph


The result will be something like shown in the image below:

Log history after a rebase. Notice the second commit from master inserted as a base commit for dev branch

Figure 2 Log history after a rebase. Notice the second commit from master inserted as a base commit for dev branch


The net outcome of both the rebase and merge command as seen above is the same i.e. integration of changes from one to another branch, here parent to child branch.
Now, naturally, the question arises as to when to use what.
Merge is a non-destructive operation that preserves the chronological order of commits verbatim. The merge command creates a merge commit which brings in a convergence point into the commit history, thereby, bringing in the context under which the integration of changes occurred. This is essential when you are working on a public project and want every developer to have a shared context.
Rebasing a feature branch with changes bought from the long-running parent branch creates a clean linear history in the feature branch. But this eliminates the context under which the activity of rebasing was done. It is preferred when you are working as part of a small team and, it is relatively easy to collaborate and communicate with all the developers about the changes done to the feature branch.



Understanding Patch in Git via Interactive Staging

Git is a super flexible version control system and offers capabilities that you may have felt the need for when working with other version control systems, but were not available. One such capability that is available is the ability to assign parts of a file in a commit, thereby, creating a logical sequence to the work done in a file over time.

Let’s understand the patch operation in Git via a simple example.

Consider a text file that you have created over time and you want the work to go in two separate commits representing a logical sequence to work:

$ mkdir PatchDemo
$ cd PatchDemo
$ git init
$ touch file.txt
$ notepad file.txt


Key in the following lines inside the file as shown in the image below:

Line 1 - Work done in first commit

Line 3 - Work done in first commit

Line 5 - Work done in first commit

Line 7 - Work done in first commit

Line 9 - Work done in first commit

Line 11 - Work done in first commit

Line 13 - Work done in first commit

Line 15 - Work done in first commit

Line 17 - Work done in first commit

Line 19 - Work done in first commit

Line 21 - Work done in first commit

Line 23 - Work done in first commit

Line 25 - Work done in first commit

The reason why we are introducing text in this fashion is to allow sufficient room for Git to differentiate between the work done in different logical sequences. In Git terminology, the work that needs to go in a certain patch is called a hunk. A patch can contain several hunks.

For text to be considered in different hunks, there needs to be a large enough difference between pre-existing work and new work meant to go in a hunk. Hence alternate lines in the original file would constitute a somewhat large enough body of pre-existing work.

Now let’s commit the work done:

$ git add file.txt
$ git commit -m “First commit consisting of work done in file.txt”

Now let’s modify the file:
Line 1 - Work done in first commit
Line 2 – Work done in second commit
Line 3 - Work done in first commit

Line 5 - Work done in first commit

Line 7 - Work done in first commit

Line 9 - Work done in first commit

Line 11 - Work done in first commit
Line 12 – Work done in third commit
Line 13 - Work done in first commit

Line 15 - Work done in first commit

Line 17 - Work done in first commit

Line 19 - Work done in first commit

Line 21 - Work done in first commit

Line 23 - Work done in first commit
Line 24 – Work done in second commit
Line 25 - Work done in first commit

Now let’s do the interactive staging of the file.txt and use the patch functionality to stage file.txt for two separate commits:

$ git add -i

This will start the interactive staging and it will look somewhat like in the following figure:

Patch using Interactive Staging

Once you enter interactive staging, you will be asked to choose from several options viz. status, update, revert, add untracked, patch, diff, quit and help. You need to choose “p” or number 5 to perform a patch.

Once that is selected, git presents you with a list of files that are available in the repository. Note, that in this case we only have one file and it shows the status of the file as consisting of 3 unstaged changes. You need to enter the serial number of the file you want to patch, thus, in this case, that would be 1.

Git will show an asterisk next to the selected file and will ask for permission to move further. You need to hit enter once to permit Git to move ahead.

Once we permit to parse the file, Git will present you hunks i.e. changes that the file contains that are not available in its last committed version. The lines in green show the changes, while the ones in white show the pre-existing work. Just below the hunk is the query posted by Git, and presented with one letter acceptable answers. If you want to know more about the meaning of those letters, press “?”. It will present you with the meaning of all those options like in the following figure:

Patch Options

In our case, we want to stage the first and the third hunks. Git then moves forward and presents you the next hunk. In the second hunk, we have the line added “Line 12 – Work done in the third commit”, and accordingly we would preserve it for the third commit. So you need to press “y” for the first and third hunks and n for the second hunk.

Once you are done marking the hunks that need to go into a commit, you will be re-directed to the initial menu. This time, press “s” for getting the status and you would be presented something like shown in the following figure:

Status on Patch

We can see in the image that now we have staged two changes and one remains unstaged. The staged changes are the two hunks that we staged in our previous steps of selecting hunks, while the one unstaged change is the hunk that we did not selected to go into our patch.

If you run a diff, then you will be able to see the changes that will go into the next commit, appearing in green and the existing work appearing in white, as shown below:

Diff of staged changes

Now let’s quit this interactive staging utility and run git status. This would give us something like shown in the following figure:

Git Status

The reason Git is showing the same file in the staged and unstaged form is, because we have staged only part of the file in the form of the selected two hunks.

Now we can go about our business as usual, and make two commits – The first commit consisting the two selected hunks and the second commit having the rest of the changes, as shown in the figure below:

Final Commits

As you can see the first commit carried two changes and the second commit carried a single change. Once we are done with the two commits, there were no changes to be committed any further.

How to Operate Multiple GitHub Accounts from a Single Computer

Developers love to use a single computer for all their needs, whether they are related to office work or work on their personal projects. Since using version control is a cardinal requirement in any software project, personal or professional, it becomes imperative that a requirement arises, whereby, a developer is required to operate multiple GitHub accounts from a single computer.

Consider a scenario that you have two GitHub accounts – one sponsored by your employer and the other one personal and you want to use a single computer to operate both of them. This is possible by virtue of SSH keys and setting remote repositories under the correct SSH key. The following is the broad outline of the article:

1. Setting up SSH keys

2. Setting up a configuration file to use easily co-ordinate among multiple accounts

3. Setting remotes correctly

1. Setting up SSH Keys

SSH keys generated using RSA algorithm, generates a pair of keys – public and private. Per the norm, the private key remains secure with you and never travel over the wire, while public key is distributed for verification. In this case the public key is stored in your GitHub account.

On Window 10 open Git Bash, navigate to C:\Users\YourMSID\.ssh and key in the following command:

$ ssh-keygen -t rsa –b 4096 -C "your personal email address"


This will prompt you to create a new file. Provide a suitable name to the file so you are able to differentiate between various files and hence various keys. Also make sure to enter a suitable passphrase. Providing passphrase further encrypts the private SSH key using a symmetric encryption algorithm, and will render the theft of the private key useless.

Now generate a key-pair for the official account in a manner similar to described above:

$ ssh-keygen -t rsa –b 4096 -C "your official email address"


The next step after the generation of the key-pair will be to copy over the public SSH keys into respective GitHub accounts. I am assuming a generic name generally given to key-pair given to personal accounts. Print on the screen and copy the relevant section:

$ cat


Make sure that you copy the key that starts with “ssh-rsa” and ends with gibberish. Do not copy the email part.

Now navigate to your personal GitHub account and open account settings. Open the “SSH and GPG Keys” section. Click on “New SSH Key”, and copy over the key. Make sure to give a suitable title to remember the computer that the key is present on. You may generate a key on some other computer tied to your personal account. A suitable title will help you connect the key and the originating computer where it came from.

Perform the same routine for the SSH key corresponding to your official account with corresponding account on GitHub.

2. Setting up a configuration file to use easily co-ordinate among multiple accounts

Now to make life easy with multiple keys stored on a single computer, we will create a configuration file containing the details about the hostname which needs to be connected to and the account details with which to authenticate. Create a config file with the following command:

$ notepad config


And copy over the following details:

# Personal
Host personal
User git
IdentityFile ~/.ssh/id_rsa_personalaccount

# Work
Host work
User git
IdentityFile ~/.ssh/id_rsa_workaccount

One very important thing to note here is to provide the hostname as given in the sample configuration and the user as “git” in both the cases.

The next step will be to make sure that SSH agent is running on the machine. Run the following command on bash shell to make it run in the background:

$ eval $(ssh-agent -s) 

This will start the SSH agent of it is not running in the background and will allocate it a process identifier. Now we will add the SSH keys for personal and professional accounts to the agent by the following command:

$ ssh-add id_rsa_personalaccount

$ ssh-add id_rsa_workaccount

If you had provided passphrases while creating the SSH keys, then you will have to provide the corresponding passphrases before adding them to the agent.

In order to make sure that we have indeed added the identities, run the following command:

$ ssh-add –l

Now that we have the keys added in the SSH agent and have the configuration file set up, we are in a position to test the authentication by connecting to GitHub with credentials as described in the config file. Ru the following command:

$ ssh –T personal

The aforementioned command will make ssh module take the config file placed in the .ssh folder by default and use host information defined therein. The result of executing the commands should be something like below:

Hi parakh! You've successfully authenticated, but GitHub does not provide shell access.

Repeat the process for the work account.

3. Setting remotes correctly

Now that we are done setting up the keys and configuration file, and have tested the authentication, we will create a dummy repository and push the changes to it. On GitHub, create a dummy repository, say, with the name DummyRepo. This will be the repository which we will use to upload our changes to, and pull the changes from. Navigate to a suitable location on your hard drive and run the following commands to create a repository mapped to DummyRepo:

$ mkdir DummyRepo
$ git init
$ touch file1.txt
$ printf “This is my file” >; file.txt
$ git add .
$ git commit -m "first commit"
$ git remote add origin git@personal:UserNameOfPersonalAccountAtGitHub/DummyRepo.git
$ git push origin master

If all the setup has been done correctly, then the push of changes to DummyRepo will succeed. Now test the pull from the repository. Create a text file over at the GitHub repository and commit it. Now run the following commands:

$ git pull origin master

This should succeed in pulling the newly created file and commit.

Hope this article was helpful to you.

How to shortlist and buy a car

In today’s market, a consumer is spoiled for choice and buying a car can be a confusing and tiresome exercise. Recently, I was in the market for a new car and wanted to jot down the process that I went through to finalize my purchase.

I will be segregating this article into different sections, and depending upon your maturity level into the process, you can either go through the entire article, or jump to the relevant section that intrigues your interest. Sections are as follows:

1. How to start your car hunt

2. Selection by features

3. Selection by budget

4. Selection by after-sales support

5. Selection by resale value

How to start your car hunt

It is advisable to foresee your requirement of a car at least 3 months prior to purchase. The reason why this period is required, especially if you are a first-time buyer, is because once you come to the conclusion of buying a new car, you will be able to better observe yourself and judge your requirements, research prospective candidate cars better, plan your finances and most importantly, have room to negotiate for the best possible deal.

There are a couple of things that you must do irrespective of the aforementioned methodology you choose to buy the car of your choice:

1. Talk and visit multiple dealerships and take at least 2-3 test drives of the cars in your shortlist,

2. Make sure that the car you test drive is not having more than 5000 Kms. on its odometer. The more a test car has been driven, the less it will reflect the true potential of a new car of the same make and model.

3. Design your test drive in such a way that the path undertaken would include heavy and moderate traffic, include at least two red light junctures and at least one U-turn. The purpose of such a design is to test the acceleration of the car when starting from a stationary position at a red light, lane changing and handling capabilities, steering feedback and get a feel for the space required to turn the car around on a U-turn. Specifications are one thing but, driving dynamics of a car can only be felt when a car is actually driven.

4. Make sure that you are using the air conditioner (summer and/or winter) of the car at the setting of your choice and observe the blower noise levels.

5. If you like a quiet cabin, then observe the Noise-Vibration-Harshness (NVH) levels both when the car is idle and when being driven. Car at idle will give you an idea of the NVH levels introduced due to engine. Car while being driven, will give you an idea about the NVH levels due to engine, tires, head wind and cross wind.

6. Do play music while test driving the vehicle. It will give you an indication of the capabilities of the music system and the level to which it can suppress noise while the car is being driven.

7. Try to schedule test drives of different cars in your shortlist in a back-to-back fashion. That will project a better comparison of driving dynamics of different cars.

8. If you have an old car, never sell that car before buying the new one. If you are planning to exchange it in lieu of the new one, then handover your old car on the day of the delivery of the new one. Due to circumstances beyond anyone’s control, a car dealership may not deliver you your new car on the promised date and if you get rid of your old car before getting a new one, then you may suffer from limited mobility and increased travel expenditure and time investment.

9. When you talk with a dealership, express your interest to buy the car in a span of two-three weeks. This conveys to a dealer that you are serious about the purchase and they will try to give you the best possible deal.

10. There are three periods in any given calendar year, which are generally the best possible times to buy a car – the month of March which signifies the closing of the financial year, festive season of Dussehra and Diwali in India (will vary from country to country), and the month of December which signifies the closing of the calendar year. Car manufacturers give the best deals in these three periods. Car manufacturers in India generally increase prices of cars from January 1 of a new calendar year, so you may want to avail the discounts that are offered at the end of a calendar year.

Start with your functional requirements whether you require a hatchback, an entry level sub-compact sedan, a full sedan, utility vehicle like an SUV, a van or a pick-up truck. Since car is something that is generally kept for a minimum period of 3-5 years, try to project your requirements, which may not exist at present. For example: You may not be having a whole lot of parking space available at the time of car purchase, which may tilt your decision towards buying a compact hatchback, but a year into the future, you may be planning to purchase a new home with a dedicated garage. In such circumstances, it is better to buy a compact sedan, than a small hatchback, which you may feel out of place or inadequate once you move in into your new home.

Selection by features

Under this method of selecting a car, you can focus on the features that you must absolutely have and features that are nice to have.

Since you are reading this article, I would humbly request that you start with safety features first and then focus on anything else. Include as many safety features as possible, and then shortlist the cars that fit the bill. In my opinion, a car bought in 2019 should at least have the following safety features:

1. Antilock Braking System (ABS) (mandatory in India beginning April 1, 2019),

2. Electronic Brakeforce Distribution (EBS) (mandatory in India beginning April 1, 2019),

3. Driver (mandatory in India beginning April 1, 2019) and co-passenger side airbags,

4. Rear parking assist (mandatory in India beginning July 1, 2019),

5. Engine immobilizer with floating code (prevents someone from copying the cryptographic keys),

6. Central locking with audible and visible door ajar warning (car honks and blinks indicators in case any car door is not closed properly when locked from outside) and distress alarm (car honks continuously and blinks indicators to attracts attention),

7. Rear de-fogger (this is a safety feature, not a convenience as manufacturers project),

8. Rear washer and wiper (again a safety feature, not a convenience),

9. Child locks in rear doors,

10. Adjustable head restraints in front and back (This again is projected as a comfort feature but is a safety feature. Fixed head restraints are generally given in entry level hatchbacks and compact sedans as a cost cutting measure and due to their small size, may not prevent whiplash injury to driver and/or co-passenger(s),

11. Rear seats with ISOFIX mounts for child seats,

12. Speed dependant auto door locks,

13. Front and rear fog lamps,

14. Day and night Inside Rear-View Mirror (IRVM) (helps reduce the glare caused by headlights at high-beam of cars coming from behind at night),

15. At least one stability system like traction control system, hill assist, corner stability system etc. which can help in manoeuvrability in speedy or tricky situations,

16. A crash test rating of at least 3 (in reference to one of the established crash testing regimes like Global NCAP or Euro NCAP)

Please note that apart from the airbags and head restraints, all the aforementioned safety measures are active-preventive in nature i.e. they help you reduce the probability of a crash. Airbags, head restraints and the physical structure of a car are passive-preventive safety measures which help passengers survive a crash.

With safety features sorted out, focus on the creature comforts. I am listing a couple of them with some rationale:

1. Automatic temperature control air conditioning (it is expensive, but saves fuel by automatically switching off the aircon when desired temperature is reached),

2. Electric power steering (better than hydraulic, as it provides for a better feedback and does not present the probability of an oil leak),

3. Height adjustable driver seat (improves visibility for short drivers),

4. Tilt and height adjustable steering (improves handling and driving comfort for short drivers),

5. Dead paddle or driver footrest (saves ankle strain when driving for long stretches on highway),

6. Projector headlamps (helps better focus light beams, plus looks cool),

7. Electrically adjustable Outside Rear-View Mirrors (ORVM) (comfortable to use),

8. Steering mounted audio and phone controls (reduces distraction),

9. Speed dependant volume control (again reduces distraction and is thoughtful engineering),

10. Distance to empty in driver information display (helps plan re-fuelling),

11. Multiple drive modes like sports, city and economy (eco mode saves fuel when on highway),

12. Seats with lumbar support and side bolstering (this is better felt than read as a specification),

13. Touchscreen enabled in-car entertainment with navigation maps (screen should be capacitive and at least 7 inches in size (measured diagonally)),

14. Wired (via USB port(s)) and wireless fast charging for mobile phones both in front and at rear,

15. Tire Pressure Monitoring System (TPMS) (helps you maintain appropriate tyre pressure which results in better road grip, superior handling, better ride quality and minimum fuel consumption)

It is always a better idea to get as many factory-fitted features as possible as you get to enjoy the manufacturer’s warranty on those items, as against to a non-existent or hard to obtain on after-market solutions. In a lot of cases, you can also avail extended warranty on a lot of features that come in factory-fitted condition.

Selection by budget

This selection methodology warrants minimum explanation. One advise that bears mention here is that it is always a good idea to keep a maximum figure in mind and then keep a 5% margin on top of the maximum figure. This will help in case the manufacturer raises the price of the vehicle or you end up selecting a variant with higher specifications.

Also keep in mind that sometimes it is profitable to finance the car purchase, rather than pay up lump-sum from personal finances. This is pre-dominantly true in a vibrant economy where you can earn more money by investing and earning interest on your principal amount and take advantage of the low interest rates on car loans. However, it makes sense to buy a car with lump-sum money if you want to save the hassle of going through paper work required to take a car loan and once the loan is paid, to get the car transferred in your name.

Selection by after-sales support

Buying a car and getting after-sales service support for the car are two different experiences. A car may be solidly built and jam packed with features but can leave a sour taste if the after-sales support is sub-par. A lot of users want top notch hassle free after-sales support for their vehicle. Fundamentally this translates into a couple of things, not limited to:

1. They want to feel taken care of when they visit the service centre. They need the service advisor to listen to the problem(s) that are facing, accurately diagnose the problem and provide a quick and cheapest resolution. A customer wants to feel pampered, not necessarily with tea, muffins and croissants, but with a caring attitude from the service staff.

2. Fast turn-around time for service. Since the car a customer has given for service or repair may be the only car that he/she might be having, it is imperative, that he/she would want the vehicle as soon as possible. One thing to note here is that, even if the turn-around time cannot be measured in hours, even if it is a day or two, a customer would appreciate, if it is accurate and service is done with focus on quality.

3. Readily available spare parts is another factor that is critical in having a fulfilling experience in this dimension.

Rely on the feedback provided by other customers in this area. Even the best of the car manufacturers can deliver a sub-par after-sales support experience. Keep in mind that at the end of the day, you will be dealing with human beings in the service centre and they may be having a bad day. Give them at least two separate chances to serve you, and then decide for yourselves. In case you get a consistently bad experience from a service centre, change the service centre.

Selection by resale value

If you are the kind of person, who likes to change his/her car every few years (read 2-4 years), your decision may also get affected by the perceived resale value of the car in the market. Some cars, even though have everything better than their rivals, fetch poor resale value in the market owing to a negative perception. That perception may be due to lack of perceived reliability, cost of maintenance, lack of after-sales support service centres, or a combination of all the aforementioned factors. In such kind of circumstances, it is best to stay away from such a car and go with one which may be your second choice but would fetch your greater resale value.

If you intend to keep the car for as long as possible, then you can overlook this factor.


I hope this article gave you some insight in a succinct manner on what selection criterion you may use for your next car purchase. It is in no way exhaustive, but definitely will nudge you in the right direction.

Raspberry Pi and Passwordless SSH Login

In any modern operating system when you login, you are greeted with a login screen asking for your credentials. If you are the only user using the system, you may be spared the labor of filling in the username, but a password still will be required to login.

We can forgo the exercise of filling the password by virtue of asymmetric encryption. Asymmetric encryption makes two types of keys available – private and public. As the name suggests, public key can be made available to the public while the private key remain with the system which needs to do the authentication. In our case we will be logging into Raspberry Pi using SSH and will use key based authentication mechanism to login, forgoing the need of any password. Pi will send the public key over the wire to the host operating system running Putty which will then compare it with the companion private key. If a match is found, the user authenticates successfully. Note that the private keys never travels over the wire.

We need the following to make this a possibility:

1. PutTTYgen: To generate a pair of keys,

2. Pageant: To run in the background and maintain availability of the private key

Both the aforementioned software components come bundled with Putty, so if you have Putty installed, there’s a good chance that they are already installed on your system.

Generating a key pair

Open PuTTYgen and click on the “Generate” button generate a pair of keys. Make sure that “RSA” algorithm is selected with key strength of 2048 bits. Once generated, use the in-built facility and save the public and private keys to the folder which you consider save enough to retain your private key for future reference. DO NOT SHARE YOUR PRIVATE KEY WITH ANYONE.

Generate key pair with PuTTYgen

Now, the most important part. If you look at the format of the public key saved by PuTTYgen, you will find that it spawns multiple lines. It is un-usable in majority of the systems and exists only for reference. We need to copy the public key in the large “Key” window, which specifically makes the key properly formatted for use in OpenSSH based authentication systems.

02 PuTTYgen Keys Window


Copy the key into a simple text file and name it “authorized_keys” and remove the txt extension. This is the file that will be used by Raspbian Stretch operating system without any further configuration.

Now run the Pageant agent in your Windows system and add the private key generated previously. The private key should have an extension “ppk”. Pageant agent will run on the host operating system where from you want to connect and will keep the private key handy.

03 Pageant

Configuring Raspberry Pi

Now let’s configure our Raspberry Pi to accept key based authentication. Login the usual route with your username and password and follow the steps:

1. Create a .ssh folder (hidden folder) in the home directory of the user for whom you want to use key based authentication.

2. Copy over the public key (NOT PRIVATE KEY) that you generated previously and named “authentication_keys” to the folder. I used a thumb drive for the purpose.

3. Secure the key file and the .ssh folder. Only the user meant to use the key based authentication should be able to access the key file in read-only and executable capacity. The .ssh folder should be off limits to everyone else.

4. Restart the ssh service.

5. Logout and log back in with the username for which you enabled the key based authentication.

mkdir .ssh
sudo mount /dev/sda1 /mnt/usb
cp /mnt/usb/authorized_keys .ssh/
sudo chmod 500 .ssh/authorized_keys
sudo chmod 700 .ssh
ls -al /home/parakh .ssh/authorized_keys
sudo systemctl restart ssh


04 Commands Cropped












All this was made possible by the magic of asymmetric encryption.

05 Login Cropped

The good thing about this scheme is that if, for some reason the public key on Raspberry Pi gets corrupted, or the Pageant is not running in the background on the host operating system, then you get offered the good-old password challenge. I purposely exited the Peagent and as expected Pi challenged me with a password corresponding to my account.

06 login using password cropped


1. Passwordless SSH access

ASP.Net Core MVC on Raspberry Pi

Key Takeaway:

.Net Core allows for a cross platform operation of applications on supported hardware and software. This extends to ASP.Net Core. In this post I am going to show how to run ASP.Net Core in self-contained deployment mode on Raspberry Pi 3.

Read On

In my last post I showed how to run a .Net Core console application in Raspberry Pi. In this post I am going to show how to run an ASP.Net Core Web application on Raspbian Stretch operating system using Raspberry Pi 3 hardware. Before you do that make sure that you have assigned a static IP address to Pi. You can learn how to do that in one of my previous post.

First create a new ASP.Net Core Web application project in Visual Studio which does not rely on any kind of authentication.

ASP.Net Core Web App

ASP.NET Core Web Application

02 No authentication

Web application with no authentication

Since the aim of this post is learn how to run an ASP.Net Core application on Pi, let’s keep things simple. We will not do any modification to any of the pages in the application. Build and run the application locally to make sure that it works.

03 ASP.Net Core app running

Web application running out of the box

The application is running locally using IIS Express and listening at the address mentioned in launchSettings.json file under Properties in the project hierarchy. When it comes to hosting the application in Pi, we need to makes sure that the application listens at the desired IP address and port. This is accomplished using the “UseUrls” method in Program.cs file. The “UseUrls” method specifies the URL scheme that the web host will use to listen to the incoming requests. Since we will be using the Kestrel web server via terminal in Pi, it is important that we change the port in the Program.cs file, as shown in the image. Make sure that the port that you assign is not in use by some other app in Pi.

04 Program.cs file

Change the port to something that is available in Pi

Now publish the entire application for linux-arm combination using the following command:

dotnet publish -r linux-arm


Now copy the entire publish directory to Pi. This will give us not only our application, but also the server infrastructure to serve the application. Make sure that you have the appropriate permission to run not only the application, but also the Kestrel server under your account. You can use the following command to recursively allow your account have the execute permission on all the assemblies inside the publish folder.

chmod –R 755 publish


Once that is done, execute the application:

05 Kestrel running

Kestrel running

Now hop into your browser in your computer and use the IP address of your Pi in conjunction of the port on which the Kestrel server is listening.

06 Application running locally

ASP.NET Core Web application being served by Pi

Happy exploration.

Running a .Net Core Application on Raspberry Pi

Key Takeaway

Raspberry Pi is an experimenter’s dream come true. It offers light to medium computing power in a small form factor with all the bells and whistles like Wi-Fi, Ethernet, Bluetooth, USB 2.0 ports etc. Further augmenting a tinkerer’s abilities are the software capabilities, which now stand further extended due to the introduction of .Net Core which allow you to leverage your existing background with Visual C# and run code on ARM architecture. In this post we will take a look at all the steps that one has to perform to run code created using Visual C# and targeting .Net Core on a Raspberry Pi 3.

Read On

.Net Core is a cross platform offering from Microsoft which allows you to run your C# code on multiple hardware (x86, x64, ARM etc.) and software platforms (Windows, Linux and macOS). Of course, it does not provide universal coverage, and at the time of writing this post, industrial grade long-term support versions of operating systems are being targeted with higher priority by Microsoft. It is natural, after all those are the operating systems that organizations would be using to run their applications.

But there’s something about frugal engineering and Raspberry Pi is a prime example of that. With support from the community, it is possible to have the code made targeting .Net Core, be run on Raspberry Pi 3. Here are some of the points that you may want to read before going any further:

1. Note that the compilation targeting ARM hardware (ARM32) for both Linux and Windows software platforms are not being officially supported by Microsoft. So, have justified expectations and be prepared to get your hands dirty with some virtual dirt. See their official statement here.

2. At the time of writing this post, it is only possible to run .Net Core code on Raspberry Pi 2 and 3, and not on Pi Zero. This is because .Net Core at the moment targets ARMv7 instruction set and above for ARM architectures. Raspberry Pi 3 uses a Broadcom BCM2837 chip which uses ARMv8 instruction set, while Raspberry Pi Zero uses BCM2835 chip which uses ARMv6 instruction set. See the official statement here.

3. There is no Software Development Kit (SDK) available at the moment that helps you develop software on Raspberry Pi for Raspberry Pi, so you will have to develop your code on a supported development environment and then copy over to Pi for execution.

Alright, if you have made this far, I am assuming that you want to give it a go.

Creation of a console application

First let’s develop our application and since this will be the first time we will be running a .Net Core project in Raspberry Pi, let’s keep things simple. Fire up your Visual Studio and then create a new console application project. I named mine as “DotNetCoreOnRPi”. Just so that we can easily identify that the things are working as desired, add a line in your main program:

Console.WriteLine("This program was created in Windows 10, but running in Raspberry Pi. :)");

Save your program and open the developer console and navigate to the folder containing your project.

Any application targeting .Net Core can be executed either as a self-contained application (Self-contained deployment) packing all the assemblies that its execution depends upon, or as an application depending on the .Net Core framework (Framework-dependent deployment). You can read more about that here. We will publish our application as a self-contained application on Raspberry Pi.

Self-contained deployment

In order for the application to execute in a supported operating system, it still needs some functionality that is supported by the targeted operating system. Raspbian Stretch operating system, the official operating system supported by the Raspberry Pi Foundation, comes missing just one essential package. Run the following code to install the “libunwind” package.

sudo apt-get install curl libunwind8 gettext

Once done we need to return to our developer prompt and publish the project targeting the “linux-arm” platform by using the following line of code:

dotnet publish -r linux-arm

This will create a folder in the bin/Debug/netcoreapp2.0 named “linux-arm”. Within the linux-arm folder will be a folder named “publish”.

Copy the entire publish folder at a suitable location in your Pi. Open a terminal window and navigate to the publish folder. Make sure that you have the appropriate permission to execute the application. You can use the following command to grant the execution permission:

chmod 755 ./DotNetCoreOnRPi

Then execute the application by using the command:



.Net Core on Raspberry Pi

For now, all the official and un-official documentation points to the fact that framework-dependent deployments are not supported. Let’s hope that Microsoft starts supporting Arm32 builds officially and we can reduce the size of our deployments by relying on the .net core framework available on a system-wide basis.

Installing Plex Media Server on Raspberry Pi


Key Takeaway

In my last post I wrote about how to install and operate Raspbian operating system in a headless mode using a static IP address with the intention of starting and using services that require a static IP address. Plex Media Server is one such service which can run fruitfully on Raspberry Pi 3 Model B and use the hardware to the fullest. In this post I will demonstrate how to install Plex Media Server on your Raspberry Pi and consume media from it.

Read On

Plex Media Server as the name suggests is a media server and can serve various types of media on a variety of devices. The basic premise behind the server is to provide media to the consuming point per the capabilities of the client. For example, if you have a video file in mkv (Matroska) format and you want to see the video on an iPad, you cannot do until you transcode the file into a format that is compatible with iPad. In this case it will be mp4. Plex provides on the fly transcoding capabilities, so you do not have to wait for the entire video file to be transcoded and then see it. It instead, transcodes the file on the fly and streams it to your device.

To get started, make sure that you have the latest version of Raspbian operating system installed and Pi is configured to communicate to your router using a static IP address. Before we start, let’s make sure that the system is having the latest packages installed using the following commands:

sudo apt-get update sudo apt-get upgrade

Update command brings information about the newer versions of the packages installed in the operating system and are available in the repository, while upgrade actually downloads the packages and installs them. Please note that upgrading the packages can download a significant amount of data, so if you are on metered bandwidth, beware.

After this we need to ensure that the traffic between Pi and clients travel on an encrypted channel. For that we need to make sure that the “https” package is installed and running. Run the following command:

sudo apt-get install apt-transport-https


Plex is not officially supported on Pi, so we will download the port created by the good folks at dev2day. The first step to do that is to add the public key corresponding to the package. Run the following command to get it done:


wget -O - | sudo apt-key add -


01 Installation of Key - Cropped


I tried searching for the Plex package made for Stretch, but was not available at the time of writing this post/. So we will install the one available for Jessie. Add the package to the list of packages by running the following command:

echo "deb jessie main" | sudo tee /etc/apt/sources.list.d/pms.list


02 Correct - Inclusion in the package List - Cropped

Now update the package list so we are able to pull in the latest Plex Media Server package:

sudo apt-get updateNow get and install the package: sudo apt-get install -t jessie plexmediaserver



03 Updating the packages - Cropped


04 Installation of Plex - Cropped

We need to change the default user under which the PMS is supposed to run from “plex” to “pi”:

sudo nano /etc/default/plexmediaserver.prev


05 Change of user - Cropped

Now restart the plex service and reboot Pi:

sudo service plexmediaserver restart sudo reboot

 Once Pi comes up, go to the static IP address at which Pi operates appended by “:32400/web” and it will take you to the welcome screen. From there on you can register for an account and add media to your library. Note that creating and using an account is not necessary to use Plex.

06 Plex Installed - Cropped

Welcome to Plex Media Server on Raspberry Pi.

How to Setup Raspberry Pi Without a Monitor and Keyboard and Ethernet Cable (Headless Mode)

Key Takeaway:

Installation of the Raspbian operating system on a Raspberry Pi requires an external keyboard and mouse for providing input and an external HDMI monitor to see what’s happening. In this post, we will learn how to configure the boot media, so that we are able to leverage our existing Windows hardware for the installation and subsequent operations without requiring an external keyboard, mouse and a monitor, also known as the “headless mode”. We will also be connecting our Pi to our Wi-Fi network without the any intermediate use of an Ethernet cable and will allocate it a static IP address.

Read On:

Raspberry Pi is a single board computer that offers a fun way to learn about Linux and is capable of handling various projects that require light to medium computing power. It is one of the most favored platforms for prototyping an IoT project.

Installation of most of the Raspberry Pi compatible operating systems at the time of writing this post requires the presence of an external USB keyboard and mouse to provide input and an HDMI capable monitor to receive video feed of what’s happening. These requirements prove to be a bit of a hurdle in getting Raspberry Pi up and running. Fortunately, things are improving and creators of Linux distros are making sure that there are ways to configure Raspberry Pi to facilitate a headless install, configuration and subsequent operation with the use of existing integrated hardware like a pc or a laptop.

In this post I will demonstrate how to install and operate Raspbian operating system in a truly headless fashion using your existing Windows PC hardware. We will accomplish the following:

1. Enable SSH for logging into Pi after the first boot.

2. Connect to existing Wi-Fi with the help of supplied credentials.

3. Have a static IP address, so in future we will have the ability to reliably connect to Pi at a known address and enable us to operate services like a NAS or a media server.

4. Enable VNC server on Pi so we can remotely login into Pi and use the convenience of GUI to get things done.


To accomplish all that we need the following hardware and software:

1. Raspberry Pi 3 Model B.

2. A Windows or Linux enabled laptop or a desktop computer to download the Raspbian image to.

3. A micro-SD card to install Raspbian image onto.

4. A micro SD card reader-writer.

5. Image of the latest version of Raspbian operating system (with desktop).

6. Etcher to transfer the Raspbian operating system onto the micro-SD card.

7. Notepad++ to create configuration files. Please note that Windows Notepad won’t cut it.

8. Advanced IP Scanner to scan the network to note the subnet and ip addresses of various devices.

9. Putty to SSH into Pi after the installation of the operating system.

10. VNC viewer to remotely login into Raspbian operating system.

I am writing this post assuming that you are working with a Windows enabled computer.

Head over to and download the latest version of Raspbian operating system with desktop. Now we need to transfer this operating system to the micro-SD card.

To transfer the operating system onto the micro-SD card we will be using Etcher from Brilliantly simple to use and just works with a wide variety of image formats. Etcher can directly work with zipped images, eliminating the need to unzip the downloaded images. You can also download the portable version and use it without installing it.






Figure 1 Etcher in action

Once you have flashed and validated the micro-SD card with the operating system, prepare to perform some steps that are going to make the entire installation and subsequent operation a headless one. If you open the card in Windows Explorer, then you will be able to access the boot folder containing a few files. Since Windows does not recognize EXT4 file system, you will not be able to see or access any other of the partition on the card or any folder or file contained therein.

Enabling SSH

To enable headless configuration and operation of Raspberry Pi, it is essential that we have some mechanism to login into our Pi. SSH enables that. By default, SSH now comes disabled in Raspbian Stretch operating system. But it can be easily enabled by introducing a file named “ssh” with no extension. You do not have to bother putting anything in the file as just the presence of the file will indicate your intention to enable SSH in Raspbian at the first and subsequent boots.






Figure 2 Insert a blank text file SSH excluding any extension

Configuring Wi-Fi

One of the changes introduced in Raspbian Stretch was the ability to put “wpa_supplicant.conf” file into the boot folder which at first boot could be used to configure network settings. So open up your Notepad++ and open a new text file. Make sure to change the “End of Line” setting set to “UNIX” (Edit->EOL Conversion). If you do not change this setting, Notepad++ will use Windows end of line settings and network settings will not take effect.









Figure 3 Change the EOL setting in Notepad++ to UNIX when handling any file for Raspbian

Insert the following settings into the file:

   1: country=in
   2: update_config=1
   3: ctrl_interface=/var/run/wpa_supplicant
   5: network={
   6: scan_ssid=1
   7: ssid="MyNetworkSSID"
   8: psk="MyNetworkPassword"
   9: }

Change the country entry to the applicable one. Similarly use the SSID of your Wi-Fi network and corresponding password.

Save the text file in the boot folder and name it “wpa_supplicant.conf”. The significance this file is that it serves the configuration to the supplicant (basically hardware or software that connects to a network. More info is available here), and after the first boot gets copied into the “/etc/wpa_supplicant” directory for operational purposes. You can read more about this here (in context with Raspbian Stretch).

Now that we have taken care of SSH and Wi-Fi settings, let’s get ourselves a static IP address where we can SSH to. Boot up your Pi.

Configuring for a static IP address

Now to assign a static IP address to our Pi, we need to login into Pi at the IP address that gets allocated to our Pi at its first boot. We will use that IP address in Putty and start our SSH session and carry out further configuration to work with a static address.

We can find the IP addresses allocated to various devices with the help of the Advanced IP Scanner tool available from Famatech. The best thing about this tool is that you can run this tool without installing it, in portable mode. Boot up your Pi and then run this tool to see the IP address allocated to the device.





Figure 4 Raspberry Pi connected to Wi-Fi with a random IP address allocated

Once you have noted down the IP address allocated to Pi, use Putty or your favorite SSH tool to login into Pi.















Figure 5 SSH into Pi using the allocated IP address

The default username and password to be used for logging into Pi are “pi” and “raspberry” respectively. After logging into Pi via SSH, use the following steps to configure Pi to have a static address.


Figure 6 Successful SSH login

Now give the following command to know about the gateway (your router in this case), just to be sure that your Pi is communicating at the IP address shown by the IP Scanner. This IP address is the one that will always be used by Pi to communicate to the router.

   1: route -ne



Figure 7 Gateway IP address

Once we have noted down the gateway’s IP address, it is time to figure out the name server. This setting is stored in resolv.conf file. Use the following command to pull it up and note down the IP address of the name server.

   1: cat /etc/resolv.conf]



Figure 8 Name server IP address

Now we need to modify the file “dhcpcd.conf” file which contains the network settings that go into effect once Pi boots up. Use the following command to pull up the file in editable mode in nano text editor:

   1: sudo nano /etc/dhcpcd.conf]

You should be able to see some pre-existing but, commented out entries showing you the way to configure the settings in this file. We will create a new entry block at the bottom of the file. Use the following entries to configure your Pi to use a static IP address at boot time and communicate to your gateway and use the designated name server:

   1: interface wlan0
   2: static ip_address=”your desired IP address”
   3: static routers=”your router’s IP address” 
   4: static domain_name_servers=”your name server’s IP adderss”


Figure 9 Configure the entries with the desired IP addresses

Once the aforementioned steps are complete, reboot your Pi for the network settings to take into effect. Use the command to reboot:

   1: sudo reboot –p

Once your Pi boots up, it will acquire the configured static IP address, and you should be able to login into it, using Putty.


Figure 10 Verification of newly allocated static IP address with the help of IP Scanner















Figure 11 Using the new static IP address to SSH into Pi

Once you have gotten into Pi, pull up the raspberry pi configuration utility to configure the Pi for the following:

1. Change the password from the default “raspberry” to something that only you know. This is an essential security measure.

2. Change the setting in “Advanced Options” to allow the Pi to see and use the entire file space. By default, that is not the case.

3. Change the setting in “Advanced Options” to change the resolution of the screen to what is native to your Windows machine.

4. Enable graphical desktop at boot from “Boot Options”.

5. Enable VNC from the “Interfacing Options” setting so we can use the VNC viewer to login into Pi using the GUI capabilities of Raspbian OS.


Figure 12 Raspberry configuration utility with all the options available


Figure 13 Configuring to boot into desktop mode


Figure 14 Changing the resolution to that of my Windows machine

Once all the changes have been done, reboot Pi. Now we will be able to login into Pi using VNC viewer.


Figure 15 First boot into GUI via VNC viewer

We have accomplished all that we had set out to achieve. Now every time you will access Pi, you will be able to access it over a static IP address and login into GUI. From here-on you can go ahead and configure Pi for services that require a static IP address. Depending on your expertise level and requirements, you can completely skip the VNC part and just configure Pi to have a static IP address and operate it over SSH.

Running Redis in a Master-Slave Replication Setup

Key Takeaway:

Redis has the facility to setup replication with the help of master-slave configurations. A master can have multiple slaves and a slave can further have slaves. In this article we will focus on a simple setup having a single master and two slaves and will discuss a general usage pattern which would allow for a robust setup.

Read on:

Redis allows for configuration in two flavors:

1. With the help of a configuration file,

2. At runtime through commands.

In this article we will setup both the master and slaves with the help of configuration files, as that is something more understandable and how instances are configured in a production environment.

Download the Redis for Windows from MSOpenTech’s GitHub Release page for 64 bit architecture, or if you are having a 32 bit computer, please refer to my previous article on how to compile Redis for a 32 bit Windows environment. Put the folder having all the files needed to run Redis in C drive.

Next we are going to discuss some of the settings required to be implemented in the configuration files, one for each instance of Redis. The general architecture that I am trying to produce here looks something like the following:

Master-Slave-Client Diagram

Figure 1 Redis replication basic architecture

Explanation of the architecture:

In Redis, master instance allows for both reads and writes, and in addition to that allows for disk persistence. Slaves, by default, are read only and allow for disk persistence. Over here, since this is just an introductory article, we are going to learn how to setup the simplest master-slave configuration. A more prudent setup would allow master to engage only with memory writes, and offload disk persistence to one of the slaves, and one or more slaves will dedicatedly handle the read queries. But we will discuss this in some later article.

In order to implement the aforementioned architecture we need to create three configuration files, one for master and one for each of the two slaves.

1. Nomenclature of configuration file:

It is important to name a Redis configuration file in such a way that the purpose and some vital information contained can be gleaned off from the name itself.

We will follow the pattern: environment.type of instance.purpose of instance.port number.conf

So a configuration meant for a master instance would bear the name like

2. Creation of configuration files:

Redis master: Copy the configuration file that comes pre-packaged with Redis and rename it to, where 5555 is the port that will be dedicated to master instance. You can name it differently according to the port availability on your machine. Open the configuration in a text editor and change the default port from 6379 to the one that is available in your machine.

00 Master Configuration

Figure 2 Configure master instance to run on port 5555

Redis slave 1: Make a copy of the master’s configuration file and name it like Change the port in the file to 5556 or something that is available on your machine. Now search for the “Replication” section and un-comment the setting of “slaveof” and provide the IP address on which the master instance will be hosted and the port number. Since we will be just running all the three instances locally, the IP address should be and the port number used in the master’s configuration file. The slave instance that we will run will take it’s configuration from this file.

00 Slave Configuration

Figure 3 Configure slave instance to receive synchronization from master

Redis slave 2: Repeat the aforementioned steps, with the exception of changing the port number to 5557 or something that is available on your machine and accordingly use the same port in the name of the file. I have named mine to

3. Running instances

Redis master: Open a command prompt and navigate to the folder where you are having Redis executable files and execute redis-server.exe in conjunction with the name of the configuration where fro it is supposed to pick it’s configuration from.

01 Redis Master

Figure 4 Master instance receives requests for data sync from slaves

Redis slave 1: Open another command prompt and again run the redis-server.exe file, this time specifying the slave configuration file. This will enable running a slave instance connected to the master. As soon as the slave instance will come up, the master will receive a request from slave for synchronization of data. This is shown in the screenshot.

02 Slave 1

Figure 5 Slave 1 receives and syncs data with master

Redis slave 2: Repeat the aforementioned step for slave 1, but with the other configuration file meant for slave 2.

03 Slave 2

Figure 6 Slave 2

Now run another command prompt and run redis-cli.exe and connect to the master instance. Insert some keys in the master and query them, just to make sure, they have gotten stored. Now disconnect from the master instance and connect to the first slave hosted on port 5556 (or where you hosted it.) and query for the same keys, that you inserted in the master. You will find them. Similarly you will find the same information synchronized in slave 2.

04 Redis Client

Figure 7 Redis client shows that master and slaves are at parity


Running replication in Redis is very simple and minimal configuration. The pattern shown here, is elementary, just to give an idea about Redis replication. There are more robust architectures that should be used in production settings.