Techbuzz Times

The Ultimate Flip: Create Stunning Ambigrams Online in Minutes!

2025-12-05T00:51:00.001+05:30

Introduction: What's the Magic Word?

Have you ever seen a word that reads the same, or even as a completely different word, when you flip it upside down? That’s not a trick of the eye—it’s an ambigram! These typographic puzzles are a captivating blend of art and wordplay, perfect for unique tattoos, clever logos, or just a fun personal project.

While master ambigram artists spend hours meticulously crafting every curve, the good news is that thanks to the internet, you can create your own stunning ambigrams with just a few clicks! Forget complicated design software; here is your easy guide to generating beautiful ambigrams online.

Part 1: Understanding the Flip – Ambigram Basics

Before you jump into a generator, it helps to know what you're creating. The most popular type is the Rotational Ambigram, which reads the same (or as a different word) when rotated 180 degrees (180^\circ).

The "A-ha!" Moment

The genius of an ambigram lies in how one letter morphs into another when inverted. For example, a stylized 'N' might become a 'Z', or an 'M' could perfectly transform into a 'W'. Simple words with symmetrical letters (like WOW, MOM, NOON) are often the easiest to create, but online generators have opened the door to far more complex combinations.

Part 2: Your Go-To Tools – Online Ambigram Generators

The fastest and easiest way to create your own ambigram masterpiece is by using a dedicated online generator. These tools do the complex design work for you!

That's a great question! Creating ambigrams (words that can be read the same way or as a different word when rotated or reflected) is a fun challenge.

Here are some of the best sites and tools available online for creating ambigrams, ranging from free basic generators to more advanced paid options.

🌐 Online Ambigram Generators (Free & Paid)

1. FlipScript Ambigram Generator

* What it does: This is one of the most well-known and professional-grade ambigram creators. They use a more complex, database-driven method to generate more legible and visually appealing designs than simple one-to-one letter mapping.

* Best for: High-quality, complex, and customizable ambigrams (names, words, or phrases that read the same or differently when flipped).

* Note: While you can often create a preview for free, the final high-resolution artwork or design bundle usually requires a purchase. They also offer AI generators and custom services.

2. Make Ambigrams (Ambigram Generator)

* What it does: A free, classic ambigram generator that uses a one-to-one letter mapping principle across several available fonts (like AmbimaticHD, NSambi, etc.). It works best for one word or two words of the same length.

* Best for: Quick, simple, and free rotational ambigrams using specific ambigram fonts.

* Note: The quality can vary, but it's an excellent way to see what's possible for free.

3. AI Ambigram Tattoo/Logo Generators

* What it does: Several newer tools use AI to generate more stylized, complex ambigrams, often marketed for tattoo or logo design. Examples include Fotor's Ambigram Tattoo Generator and similar tools by platforms like Clipfly or Appointo.

* Best for: Generating ambigrams in specific artistic styles (Gothic, Calligraphy, Minimalist) and for exploring different ambigram types (rotational, mirror-image, 3D, chain).

* Note: These often offer free limited designs but may require payment or a subscription for high-resolution, watermark-free downloads or advanced features.

4. FontMeme.com Ambigram Generator

* What it does: A simple, free ambigram generator. Like Make Ambigrams, it typically relies on existing ambigram fonts to quickly generate a rotational design of your word.

* Best for: Fast, basic, and free ambigram creation using various styles.

5. The Dressed Mole-Rat Ambigenerator

* What it does: A free ambigram generator with a few different styles (like 'blocky' and 'pixel art') that allows you to input one word or two words with a space.

* Best for: Experimenting with less common, artistic styles in a free environment.

📱 Mobile App Tool (Android)

* Ambigram Studio 3.0 (Android) - This app is designed to help you create ambigrams directly on your smartphone, offering some customization and the ability to save/share designs.

✍️ Manual Creation/Design Tools

If you are serious about designing a unique, high-quality ambigram (which often requires manual adjustments beyond what a simple generator can do), you'll need professional design software:

* Adobe Illustrator or Inkscape (Free/Open Source): These vector-based programs are the industry standard for formalizing a design. You can sketch your ambigram first and then create a clean, scalable vector version using the tools.

* Sketching: Many artists recommend starting with pencil and paper. Ambigrams are visual puzzles, and sketching helps you identify letter pairings and see how the shapes can connect and transform.

Also read: Top Creative and Impressive Ambigram Design & Styles Collection

How to Use an Online Generator (The 3-Step Process)

Creating your ambigram is usually a straightforward process, no matter which site you choose:

* Enter Your Text: Type in the word or phrase you want to transform. For dual-word ambigrams (like "Life/Death"), you'll enter both words.

* Select Your Font/Style: Choose from the available font options. Different fonts work better for different letter combinations!

* Generate & Review: Click the button and wait a few seconds. Most sites will instantly display your ambigram. Be sure to use the "Flip" or "Rotate" button to check how it reads in both directions!

Part 3: Pro Tips for Perfect Ambigrams

To get the best results from your online generator, keep these tips in mind:

* Start Simple: If your first attempt with "Massachusetts" is a mess, try an easier word like "Family" or "Angel."

* Try Different Fonts: A design that looks awkward in a classic font might look incredible in a gothic or bold style. Experiment with the style options the generator offers.

* Remember the Symmetry: The best ambigrams look natural and unforced. If the design seems too heavily compromised just to make the flip work, try a different word or font combination.

* Check the Legibility: Can someone who doesn't know what it says read it easily in both directions? If not, it might need a re-do!

Conclusion: Time to Start Flipping!

Ambigrams are a truly unique form of word art that delights and confuses in equal measure. Thanks to the accessibility of online generators, you no longer need to be a master calligrapher to bring this clever art form into your life.

Whether you're looking for a personalized gift, an unforgettable logo, or just a cool new piece of art, go ahead and give one of the recommended tools a try. You might just surprise yourself with the typographic magic you create!

Beware of the Fake “RTO Traffic Challan” WhatsApp Scam - Don’t Install That APK!

2025-11-25T10:39:22.733+05:30

Beware of the Fake “RTO Traffic Challan” WhatsApp Scam – Don’t Install That APK!

In the last few weeks, thousands of Android users across India (especially in Haryana, Punjab, Rajasthan, Uttar Pradesh, and Delhi-NCR) have received an unsolicited WhatsApp message that looks exactly like an official traffic challan notice.

Here’s how the scam works:

What the message looks like

Sender name: Something official-sounding like “Challan Detail”, “RTO Traffic Challan”, “E-Challan Punjab/Haryana”, etc.

Profile picture: Usually a logo with a tractor, jeep, or police emblem to make it look authentic.

Message: Either blank or a short line like “Your vehicle has a pending e-challan” or “Pay your traffic fine here”.

Attachment: An APK file named something like

→ RTO_ECHALLAN.apk

→ TrafficChallan.apk

→ EChallan_Payment.apk (usually 10–15 MB)

What happens if you install the APK?

The moment you install and open this fake app, it is actually malware (mostly a banking trojan or spyware). It can:

Read all your SMS (to steal OTPs)

Access your contacts

Steal banking app credentials and credit/debit card details

Overlay fake login screens on top of real banking/UPI apps

Silently register your phone for premium SMS services

Drain your bank account within minutes

Real-life cases have already been reported where people lost ₹20,000–₹1.5 lakh within hours of installing such APKs.

How to identify this scam instantly

Real e-challans NEVER come via WhatsApp.

Official traffic challan notifications come only through:

Parivahan website (echallan.parivahan.gov.in)

mParivahan app (official government app)

SMS from official numbers like VM-ECHALL or VK-ECHALL

Government departments will NEVER send you an APK file to “pay” or “view” your challan.

The sender is usually a new business account “joined in the last month”.

What you should do right now

If you received such a message → DO NOT download or install the APK.

Block and report the number immediately.

If you have already installed it:

Switch off internet/data immediately.

Go to Settings → Apps → look for suspicious apps (usually named “eChallan”, “RTO”, “Traffic Police”, etc.) and uninstall.

Factory reset your phone if possible.

Change passwords of all banking/UPI apps from another device.

Call your bank and ask them to block suspicious transactions.

File a cybercrime complaint at cybercrime.gov.in

How to check real traffic challans (the safe way)

Visit official website: https://echallan.parivahan.gov.in

Enter your vehicle number or challan number

Or download the official “mParivahan” app from Google Play Store (developed by Ministry of Road Transport)

Spread the word

This scam is spreading fast because people panic when they see “traffic challan” and think they have to pay immediately. Share this article with your family WhatsApp groups, especially with parents and elderly relatives who are most vulnerable.

Remember: No government department in India will ever send you an APK file on WhatsApp to pay a fine.

Stay safe, don’t click unknown APK files, and always verify from official sources.

If you’ve been a victim of this scam, drop your experience in the comments below so others can learn.

#StopRTOScam #WhatsAppScam #FakeEchallan #CyberSafetyIndia

Some of the Best Kubernetes Memes: Laughing Through the Container Orchestration Chaos

2025-10-26T16:57:00.004+05:30

Kubernetes, the powerful container orchestration platform, has revolutionized how we deploy and manage applications. But let’s be honest—working with Kubernetes can sometimes feel like taming a wild beast. Luckily, the Kubernetes community has a fantastic sense of humor, and memes have become a beloved way to share the joys, frustrations, and quirks of this complex technology.

Here are some of the best Kubernetes memes that perfectly capture the rollercoaster ride of container orchestration:

1. The “It Works on My Machine” Meme

A classic in software development, but with Kubernetes, it’s taken to a whole new level. The meme usually shows a developer confidently saying, “It works on my machine,” while the cluster is on fire. Kubernetes clusters can behave differently depending on configurations, making this joke painfully relatable.

2. The YAML Struggle

Anyone who’s written Kubernetes manifests knows the pain of YAML indentation errors. Memes joking about how a single misplaced space can break your entire deployment are everywhere. One popular meme shows a Kubernetes user crying over a YAML file with the caption: “Indentation is not just a style, it’s a survival skill.”

3. The Pod Lifecycle Drama

Pods in Kubernetes have a lifecycle that can be confusing for newcomers. Memes often depict pods as dramatic characters—crashing, restarting, or stuck in “Pending” state forever. One meme shows a pod with a “CrashLoopBackOff” status and the caption: “I’m not lazy, I’m just taking a break... indefinitely.”

4. The Cluster Admin’s Life

Cluster administrators are the unsung heroes who keep everything running smoothly. Memes about admins juggling multiple clusters, dealing with mysterious errors, or explaining Kubernetes concepts to non-technical stakeholders are a hit. A favorite shows an admin surrounded by monitors with the caption: “I don’t always fix Kubernetes, but when I do, I don’t know how.”

5. The Helm Chart Rollercoaster

Helm charts simplify Kubernetes deployments but can also introduce their own headaches. Memes joke about the complexity of Helm templates and the feeling of relief when a chart finally installs without errors. One meme shows a rollercoaster labeled “Helm Chart Debugging” with riders screaming.

6. The “Kubernetes is the New Linux” Meme

As Kubernetes becomes the new standard for infrastructure, memes compare it to Linux—powerful but with a steep learning curve. One meme humorously states: “Linux was hard, Kubernetes is harder, but at least it’s cloud-native.”

7. It worked and i tested on my local cluster.

It perfectly captures the difference in scale, complexity, and sheer seriousness between a Production Cluster (the heavily armored, formidable figure) and a Local Minikube Setup (the charming, albeit less intimidating, Hello Kitty samurai).

Why Do Kubernetes Memes Matter?

Beyond the laughs, Kubernetes memes help build community and shared understanding. They make the steep learning curve a little less intimidating and remind us that everyone—from beginners to experts—faces challenges. Plus, they’re a great way to bond over the shared chaos of managing containers!

If you’re a Kubernetes user, you’ve probably chuckled at some of these memes or even created your own. Embrace the humor—it’s part of the journey in mastering one of the most powerful tools in modern cloud computing.

Express Your Soul: Top Hindi and Sanskrit Tattoo Designs to Inspire You

2025-10-26T14:35:00.001+05:30

Hindi Tattoos:

Calligraphy and Script Tattoos:
- Devanagari Script: Visually appealing for meaningful words, names, or phrases.
- Sanskrit Calligraphy: Used for Hindu mantras and spiritual phrases.
- Meaningful Phrases: Examples include "Om," "This too shall pass" (ये वक़्त भी गुज़र जायेगा), or "loved."
- Personalized Names: Names tattooed in Hindi or Sanskrit calligraphy.
Spiritual and Mythological Symbols:
- Om Symbol: Symbolizes peace, spirituality, and universal connection.
- Lotus Flower: Represents purity, enlightenment, and rebirth.
- Deities: Lord Shiva, Lord Ganesha, Goddess Durga/Kali, Lord Hanuman.
- Mantra Tattoos: Maha Mrityunjaya Mantra, Gayatri Mantra.
- Trishul: Lord Shiva's trident, often with Sanskrit script.
Placement Ideas:
- Wrist or behind the ear for small symbols.
- Arms and legs for medium-sized designs.
- Neck, back, chest for larger, elaborate designs.
- Forearm for script tattoos.
- Ribcage, ankle, shoulder for quotes, symbols, or names.
Design Styles:
- Bold Black Ink.
- Modern Calligraphy with bold strokes and red ink accents.
- Line Art for simple, emotional designs.
- Watercolor for vibrant floral or artistic designs.
- Minimalist for simple, meaningful designs.
- Traditional Indian Art Style for deity depictions.

Sanskrit Tattoos:

Script and Calligraphy:
- Modern Calligraphy with bold strokes and red ink accents.
- Clean and Simple Fonts for minimalist emphasis.
- Traditional Devanagari Script for names, mantras, or phrases.
- Flowing and Decorative Lines to enhance spiritual essence.
Symbols and Imagery:
- Om Symbol: Bold black ink or abstract, integrated with mandalas or lotus.
- Religious Deities and Symbols: Lord Shiva, Trishul, Lord Ganesha, Lord Hanuman.
- Mandalas: Intricate circular patterns symbolizing universe and harmony.
- Lotus Flower: Paired with Sanskrit text symbolizing beauty and liberation.
- Unalome and Endless Knot: Buddhist symbols representing enlightenment and continuity.
Text-Based Ideas:
- Mantras and Prayers: Maha Mrityunjay Mantra, Om Namah Shivaya.
- Meaningful Words and Phrases: "Breathe," "Gratitude," "Live Free," personal names, motivational quotes.
- Abstract Flow: Artistic arrangement of Sanskrit script with thick black lines.
Design Styles:
- Watercolor Style for colorful flowers or highlights.
- Minimalist for clean, elegant script or single symbols.
- Geometric blending with abstract line art or mandalas.
- Traditional Indian Art Style for deity figures with decorative motifs.

When choosing either Hindi or Sanskrit tattoos, it is important to verify the accuracy of the script and meaning to ensure respectful and meaningful representation.

1. Aham Asmi Yodhah
Sanskrit: अहमस्मि योधः
Meaning: I am a warrior

2. Anuugacchantu Pravahang
Sanskrit: अनुगच्छतु प्रवाह
Meaning: Go With the Flow

3. Tatparivartanam Bhav

Sanskrit: तत्परिवर्तनं भव
Meaning: Be the change

4.Abhaya
Sanskrit: अभय
Meaning: fearlessness, no fear

ॐ (Om)

Meaning: The sacred sound representing the universe, spirituality, and peace.

प्रेम (Prem)

Meaning: Love

शक्ति (Shakti)

Meaning: Power or Strength

साहस (Sahas)

Meaning: Courage

धैर्य (Dharya)

Meaning: Patience or Endurance

मुक्ति (Mukti)

Meaning: Liberation or Freedom

जीवन (Jeevan)

Meaning: Life

सपना (Sapna)

Meaning: Dream

विश्वास (Vishwas)

Meaning: Faith or Trust

यह भी गुजर जाएगा (Yeh Bhi Guzar Jayega)

Meaning: This too shall pass

माँ (Maa)

Meaning: Mother

परिवार (Parivaar)

Meaning: Family

शांति (Shanti)

Meaning: Peace

सपने सच होते हैं (Sapne Sach Hote Hain)

Meaning: Dreams do come true

जीवन एक यात्रा है (Jeevan Ek Yatra Hai

Meaning: Life is a journey

Configuring a Static IP for VirtualBox VM in Ubuntu along with Internet Connectivity in Virtualbox

2024-05-11T21:10:00.000+05:30

Configuring a Static IP for VirtualBox VM in Ubuntu along with Internet Connectivity in VirtualBox

If you have provisioned any Ubuntu Server/VM running using Oracle Virtual box and want to have both static IP and Internet connectivity enabled. This is the right place for you to learn how to make the required configurations to achieve this.

For this task, we will need to add two Network adaptor , If you also need your VM to have internet access as well, leave Adapter 1 as NAT and enable Adapter 2, configured as a Host-Only adapter. This will allow your VM to connect to the internet using NAT as well as make a local connection to your Host using Host-Only.

1. Adaptor 1 - NAT

2. Adaptor 2 : - Host only adaptor

Steps:

1. Shutdown/ Power off the VM

2. Go to the VM settings and Select adaptor 1 as NAT as shown in the below screenshot.

3. In the advanced setting, select the port forwarding and configure port forwarding as below

for the 'NAT'. I clicked the 'port forwarding' option at the bottom of the screen. I gave it a name 'PuTTY-port-fwd', protocol TCP, host IP 127.0.1.1 host port 2222 guest IP 10.0.2.15 guest port 22. I then launched PuTTY and set it to 127.0.0.1 port 2222 and it connected to my ubuntu vm

4. Power on the VM and let it boot until login prompt is available , Open any putty terminal, i use mobaxterm for the ssh access.

Verify ssh access using ssh -p 2222 himanshu@127.0.1.1

Booyeah! you have successfully configured your Ubuntu VM to be accessible via Putty session along with the internet access.

I hope this post was helpful for you.

Also read :

Assign static IP address to Centos/RHEL 7 Virtual machines in Oracle VirtualBox

Passed CKA exam with 87% marks in First attempt

2023-12-29T01:10:00.001+05:30

Hi all, today we are going to talk how you can prepare and pass the CKA exam with great marks.

Last month in November, i scheduled and passed the CKA exam with 87 percent marks.

I will share the tips to crack the CKA exam in the first attempt.

Why CKA

CKA that stands for Certified Kubernetes Administrator is one of the toughest exam in the mark since this is practical scenario based exam and it examines your real time problem solving skills based upon 15 to 20 exams with different weightage. Kubernetes is used for most of the digital business for deploying their applications. So, if you are into DevOps, Site Reliability (SRE), Platform engineering, Kubernetes is a must skill and passing the CKA exam and adding this badge to your portfolio will really add more value.

Course used to Prepare

Udemy Certified Kubernetes Administrator (CKA) with Practice Tests by Mumshad Mannambeth is the one of the best available course if you want to Learn kubernetes concepts in deep and want to further give the CKA exam.

Link to the course here : Udemy Certified Kubernetes Administrator (CKA)

Course length or duration is decent, so depending upon your speed, it may take up to 2 months to complete all the chapters or topics. During each topic, you will get chance to gain hand-on and gain practical by doing the lab practice on the kodekloud that comes with this course.

The same course can be purchased from Kodekloud as well.

At the end of the course, you will have three practice tests that will test your overall knowledge and exams questions difficulty is similar to the actual CKA exam.

You may not get good marks during first attempt of these practice tests, however try to solve them as much as you can and gain speed to solve the questions.

Once you are satisfied that you can solve these practice tests without any issues, its time to move on to the next step that is killer shell simulator exams.

Make use of the free killer shell simulator exams

During the CKA exam purchase, it comes with two sessions of killer.sh exam simulator. You will get two lab sessions, each of the session will be available for 36 hours.Please note that both the sessions will contain the same questions.

Treat this as your actual exam and solve the questions as much you can with speed and try to finish in two hours. This can help to analyze how you are doing and if ready with actual CKA exam.

Personally, i found the killer.sh exam level is more difficult than the actual CKA exam.I managed to score 70/125 in my first killer.sh exam

Make sure to practice again and again all the questions and solve all of these during the 36 hours, i tried this exam three times and scored 90 and 121 in them.

Register for the exam

Once you are confident, go ahead and schedule the exam in your preferred time zone.

Exam is conducted by PSI Bridge Proctoring Platform.

One of the important tip, do not try exam in your company's laptop/machine, always use your personal machines to avoid any technical issues.

During the exam, you will need to confirm your identify by showing a government ID like driver license, Passport etc.

Once initial verification is done, exam will be presented to you.

I got 17 questions to solve on 120 minutes and i was able to solve maximum before the time except 2 questions that gave some trouble, so the main thing is avoid the questions that you are not able to solve and keep them for the last to avoid time wastage.

Other Tips

Kubernetes Documentation : You are allowed to use the kubernetes documentation for CKA, feel free to use that if required. It can certainly helps to gain the yaml file for many of the questions.

Create alias for dry-run=client - o yaml : this will also help to save time for may questions.

export dr=‘–dry-run=client -o yaml’

Don't create too many alias: By default, there will an alias k for kubectl, do not waste time to create alias for every command, it may confuse and will waste time.

I hope all the above info have helped you to gain some insights on the CKA exam. Please feel free to comment down any questions you have related to the CKA exam.

Good Luck

Assign static IP address to Centos/RHEL 7 Virtual machines in Oracle VirtualBox

2021-01-06T02:25:00.004+05:30

Hello readers, in this post we will learn how we can set up static IP address to the Virtual machines created using Oracle Virtual Box.

In case you want to install Oracle Virtual Box and deploy a Linux VM like Ubuntu or Centos on it, please read old post with detailed steps.

When we created these virtual machines, they have IP address assigned which are from the bridged adaptor on my Wi-Fi router network. So, the ip address that my virtual machines are getting are assigned by the Wi-Fi router using dhcp. As the IPs assigned by the DHCP router are dynamic so they can change anytime when you reboot the machines. Sometimes, when you reboot the machines, you will find that the IP address assigned got changed than the one they had before.

So, in case you want to have your virtual machines to have static IP address, this cannot be achieved using the bridged network, so a alternate way is to create another network that will be host only network.

It will be a network on my Laptop and my laptop will have a virtual interface on that network and all of the virtual machines will have a virtual interface on that network and we can assign static IPs for the VMs on that network.

In this post, we have performed steps on CentOS 7.9 Linux VM.

Open Host Network Manager from the File menu or Network option from the Tools menu

Host only Ethernet Adapter

Here you will see list of Host only networks that are already created, sometimes you will one of the default as shown in screenshot below already created, else you can create new host only ethernet network.

In this case, i am going to use default one with IP address range 192.168.56.1/24 Make sure dhcp server option is unchecked.

Once you have identified the host only network, you need to attach this network to your virtual machines. Right click on machine and choose settings and go to network.

Adapter 1 with Bridged Network for internet access

In the adapter one, you can see it is attached to Bridged network which is required for internet connectivity if you want to download any packages.

Go to Adapter 2 and select attached to : Host-only adapter , leave everything else as default.

Now we have two adapter attached to the machine, one is the bridged router and second one is host only adapter. Click on OK and power on the Virtual machine. You will see a new interface is attached and verified using the ip a s command or ifconfig command, however IP address is still not assigned to the interface.

Also read: Different instructions in Dockerfile and their usage

Configure Static IP Address in CentOS 7 / RHEL 7

Perform below steps to create a new config file for the newly added interface enp0s8

# cd /etc/sysconfig/network-scripts# vi ifcfg-enp0s8

Add below to the ifcfg-enp0s8

NAME=enp0s8

DEVICE=enp0s8

BOOTPROTO=none

DEFROUTE=yes

ONBOOT=yes

PREFIX=24

IPADDR=192.168.56.2

save and quit the file.

Restart the network service using below command

# systemctl restart network

Now, you will see that IP address 192.168.56.2 given in the config file is plumbed on the interface enp0s8

You can reboot the machine and test ssh via IP, You have successfully assigned static IP address to your Centos 7 /RHEL Linux machine.

Steps to Clone Virtual Machines in Oracle VirtualBox

2021-01-05T19:02:00.003+05:30

Hello readers, in our last post, we learnt about installing Oracle Virtual box and deploying a Centos 7 Linux machine using the vdi image. In case you have a scenario to create multiple machines with similar configurations, you don't need to repeat the steps to install or deploy a new machine. You can use Cloning feature of Virtual Box to create more machines.

I was setting up a Lab environment for creating Kubernetes cluster and deployed machine 1 on Oracle Virtual box, to create remaining nodes of the cluster, I used the cloning feature of Virtual Box t that is a really great feature.

Steps to Clone a Virtual Machine in Oracle Virtual machine

Power off the machine that you want to clone. Make sure the virtual machine is powered off before starting the clone steps else the option will be greyed out or disabled.

Right click on the machine, you want to clone and click on Clone option.

In the next step, you will come across below UI , Enter the name of machine and I have used the Mac Address Policy as "Generate new MAC addresses for all network adapters"

This option makes sure that the clone VM don't get the same MAC address assigned as that of the source VM

You may leave the Additional Options unchecked.

In the next step, you need to choose between Full clone or Linked clone, Full clone creates a full copy of your virtual hard disk while linked clone does not create full copy of virtual hard disk and helps to save disk space.

For my use case, Linked clone option was fine. You may use Full clone option as well depending upon your case.

Click on clone option and instantly your source VM will be cloned.

Power on both machines and they are ready to use.

Also read : 40 Linux commands for Beginners and intermediate users

Hope you are able to do the clone of your virtual machine following these steps.

How to apply and get Color coded stickers for your vehicle in Haryana with steps

2021-01-03T02:48:00.001+05:30

Ministry of Road transport and Highways have made a move last year to have High Security registration Plate and color coded stickers affixed on your vehicle for all the vehicles that have been sold before April 2019. The idea and goal behind this move is to prevent Vehicle theft and easing the tracking. Violators are being fined for Rs 5500 in case the vehicles are not fitted with both High security registration plate or color coded sticker.

In case you already have the High security registration plate (HSRP) and just want to have color coded sticker for your vehicle, the process to get it is quite simple that we will see in this post.

The process has been simplified and made online, Just apply for the color coded stickers on www.hsrphr.com and make the payment online and choose a time slot/date as per your convenience and get the same on the chosen time.

Note : Keep the Front and Rear Laser code of your HSRP handy with you, you can find it as shown in image below.

This post explains the steps for Color coded stickers for vehicles based in Haryana via hsrphr.com, you can also try bookmyhsrp.com that is nation wide site.

Follow the steps as given below:

Go to website https://www.hsrphr.com/ and choose the option for the color coded sticker or Go to website https://www.hsrphr.com/sticker/BookingDetail.aspx link directly to go to sticker booking menu

Fill the details asked in step one that is the Vehicle Registration number, Last 5 digit of Chassis number and Engine number. Enter the captcha code and hit on Click here.

Next, it will automatically fill some details like BS number, Vehicle registration date, Fuel type, Vehicle company, type and Category.

In the next step you need to choose the Fitment location that is most feasible to you. I am based in Faridabad currently, hence I choose the nearest option to me.

Once you have selected the Fitment location, confirm the date/slot as per your feasibility. The most recent available was 24th February for me, however I selected 6th March as I wanted weekend.

Review the Booking summary and click on confirm and proceed.

In the next step, you will see the total cost and breakup of the cost with taxes. The total cost for my car came out to be Rs 146.88

Agree to the terms and conditions and go ahead with the payment.

Once payment is completed, you will get SMS and email regarding the registration confirmation with a summary and a receipt that is valid 2 weeks extra than your booked date. This receipt can be shown in case you are asked by anyone regarding the Color coded stickers for your vehicles.

Please note you need to carry the receipt and RC copy on the day of the appointment

Install Oracle VirtualBox and deploy Centos 7 machine with screenshots

2021-01-01T02:09:00.017+05:30

Install Oracle VirtualBox on Windows 10 Laptop and deploy Centos 7 machine with screenshots

Hello and welcome to this blog post, In this post we are going to learn how we can set up a Lab environment on our Laptop. We are going to use Oracle Virtual box to setup a lab with a virtual machine and Centos 7.9 installed on it.

You can choose VMware workstation as well or any virtualization technology you are comfortable with as an alternative option to Oracle VirtualBox.

Install VirtualBox on your Laptop

Download the Oracle Virtual Box software and install the same. It is supported for Linux, Windows, Macintosh and Solaris

Download page : https://www.virtualbox.org/

Go to the download page and install the software for the Laptop OS , in this post we have used Windows 10.

Once downloaded, run the executable and setup wizard, installation is very easy. Click on the installer with .exe and click on next.

Click next and select the location. We are going to set the default options.

Finally read the warning about the network interfaces, its going to reset the network connection.

Click install and it goes through the installation process and it finishes in a minute

Once installation is finished, you will see the Oracle Virtual Box interface as shown below

How to install/deploy a Centos Machine on VirtualBox

To deploy the virtual machine, you need a image of the OS you want to deploy. In this demo, we are setting up Centos 7.9 machine.

Download the image from https://osboxes.org/ There are lot of images available for different OS versions, if you want to download centos image, go directly to https://www.osboxes.org/centos/

It will download a compressed .7z file and it takes about 1 GB space. Once downloaded extract the .7z file. You will find the centos vdi image in the 64bit folder.

Now go back to Oracle virtual box and start deploy the centos machine.

Click on Machine - New

It will bring below interface, here you need to specify the name and the OS that you want to install.

Choose Redhat 64 bit as version.

In the next step, select the memory size you want for your machine, i have used 2 GB for my centos 7.9 machine.

I am going to go ahead and select the hard disk, i have used Use an existing virtual hard disk and browse to the path where you have centos vdi image downloaded.

Click on choose and create

Now, it has deployed the centos image or Centos virtual machine.

Before powering on the Centos machine, update the settings options and select the network option and set the network type to bridged. By default, you will find it as NAT.

Update the same and set it to Bridged Adapter and adapter that is going to be bridged to is my wifi router.

You can now proceed to start your virtual machine.

You can now proceed to login to your machine, the password is same as that of user i.e osboxes.org in lowercase.

Hope you are able to deploy centos Linux machine following this tutorial. Feel free to comment in case you are facing any issue or having any doubt.

Also read: Creating Virtual machines in KVM using GUI tool

How to install R and RStudio on Linux - CentOS or RHEL 7 in 5 minutes

2020-12-06T02:08:00.000+05:30

R is a programming language used for statistical computing commonly by Data Scientists and analysts. It is free and open source tool under GNU project and R is maintained by R foundation.

In this article we will learn how to install R and R Studio on a Linux server that can be Centos 7 or Red hat Enterprise Linux 7.

Please note : You can install either using root user or a non root user with sudo rights.

Step 1 : Install R

First, you need to install the epel repo for centos and rhel using below command. Make sure yum works on your machine.

sudo yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm

Install R software using below command

sudo yum install R -y

Once yum completes the installation of R package, you may verify the same using below command.

On your Linux machine, run command R, if successfully installed you will see output as given below.

root@techbuzztimes #  R

You are done with one part that is R installation, next you need to install R studio.

Step 2: Install R studio

You can find the latest version of R studio for Centos and RHEL 7 from here

Make sure wget is installed on your machine, you need to download the package first and then install it using yum command as given below

wget https://download2.rstudio.org/server/centos6/x86_64/rstudio-server-rhel-1.3.1093-x86_64.rpm

sudo yum install rstudio-server-rhel-1.3.1093-x86_64.rpm

During the installation, at the end it will try to enable and start the service as shown in below screenshot, make sure Rtsudio service is up and running.

Check the Rstudio service using below command.

systemctl status rstudio-server.service

Make sure service is enabled so that it comes up after the server restarts.

systemctl enable rstudio-server.service

Step 3 : Verify Rstudio GUI

Ok, so you are done with the installation steps, now you can go ahead and verify the R studio gui on web browser.

By default, R studio runs on port 8787

In your web browser open URL http://hostname:8787

You will see gui like below

You can verify access on the R studio using any user, make sure user exists on the server and having valid home directory on the server, you may check using below command.

getent passwd username

Once successfully logged in, you will see Gui as shown below. All these steps will take between 5 to 10 minutes. Please let us know how your R studio installation went in comments.

How to Register Philips Trimmer Warranty Online using Serial Number

2020-03-16T00:14:00.001+05:30

Few days back, i have purchased my new Philips trimmer Online Philips QT4011/15. My last trimmer QT4019/15 worked really well that i purchased back in 2012. Philips is a brand that you can trust without second thought. They have good range of trimmers and comes with reasonable price tag. You can purchase Philips trimmer on all the major Online Websites or from Offline stores.

In this post, i will show you how you can register your Philips trimmer on Philips India website and get 3 years warranty for it.

1. Go to Philips India website, Sign up for the same by entering your details or if you already have account, log in with the credentials to start registering your Philips trimmer.

Link of Philip India Website: https://www.philips.co.in/myphilips/login#tab=log-in

2. Once you land up on the home page after login, you will see the old registered products and below that there is option Register your product. Click on the Register your product option and enter the serial number if you have the same.

In my case i wanted to Registered my Philips QT4011/15 Trimmer that i purchased online from Flipkart , i tried couple of product codes given on the package but sadly none of them worked.

So, i searched for the product Philips QT4011/15 and it showed me below page.

3. Enter below details to complete the registration. Give the Date of Purchase as the date when order was placed. Enter the serial number that is 4 digit code given on the trimmer as show in the below screenshot.

How to get serial number of your Philips Trimmer:

As shown in below screenshot, serial is at the back side of the trimmer. The 4 digit code will be the serial number for your trimmer.

Post entering all the details, you will see the confirmation page as show below.

If you find, this post useful, do like us on Facebook, twitter.

How to install Docker on RHEL 8 beta

2019-12-02T17:23:00.000+05:30

Introduction

This post will guide you about the steps required to get started with Docker on RHEL 8 beta system. RHEL 8 beta was announced a few months back and it is available to download for testers and developers, It comes with a lot of advancement and new features and If you want to install and explore RHEL 8 you can read our old post that shows the detailed steps of RHEL 8 installation on VMware workstation

One of the new features added in RHEL 8 is Containers without daemons. Buildah and Podman can help you build containers without any requirement of Dockers.

There are two versions of Dockers available: Docker CE [Community edition] and Docker EE [Enterprise Edition].

Well, if you are wondering of RHEL 8 Beta supports docker? There is no official documentation regarding the installation of Dockers on RHEL 8 beta, we tested installation of Docker CE on RHEL 8 beta to play with dockers on RHEL 8.

Steps of Installing Docker CE on RHEL 8 beta

Before installing Docker CE on a machine, we need to setup the docker repository. Once this step is done, we can install Docker from the repository.

1. Set up the repository

Install required packages, dnf-utils, device-mapper-persistent-data and lvm2 are required by the devicemapper storage driver.

Note that : DNF (dandified yum)is used as package management utility in RHEL 8.

# dnf install -y dnf-utils \
  device-mapper-persistent-data \
  lvm2

Use the following command to set up the repository.

#  dnf config-manager \ 
  --add-repo \
  https://download.docker.com/linux/centos/docker-ce.repo

Now, the docker ce repository is set up, you can check using dnf repolist or yum repolist

2. Install Docker CE

You can install the latest version of the docker ce using below command.

# dnf install docker-ce

While installing, if you are prompted to accept the GPG key, accept the same by entering y

Note: We encountered below error while running the install command for the first time. We re-ran the install command, it did not appear and prompt for accepting gpg key came next and after entering y, the installation went smooth and was finished in about a minute.

Curl error (6): Couldn’t resolve host name for https://download.docker.com/linux/centos/gpg [Could not resolve host: download.docker.com]

Once installed, you will see the download complete message with the package details that are installed.

Next step is to start and enable docker using systemctl

# systemctl start docker
# systemctl enable docker

Finally, you are done with the Docker CE installation on your RHEL 8 machine, now lets verify that it is installed correctly by running the hello-world image.

That’s all for this post, hope you are able to install docker on your RedHat Linux 8 machine.

If you have thoughts on this, please feel free to comment below.

Different Instructions in a Dockerfile and their usage

2019-11-28T16:29:00.000+05:30

Learn about different components/Instructions that makes a Dockerfile

What is Dockerfile?

The set of instructions for building a container are written in Dockefile. It is a text file that contains the base image, all the settings, and the list of commands required for preparing and starting a container.

Dockerfile basic Example

A basic example of a Dockerfile for installaing and building a apache web server.

FROM centos:latest

MAINTAINER admin

RUN yum update && yum -y install httpd

RUN echo "Hello, Welcome to the world of Dockers" > /var/www/html/index.html

EXPOSE 80

CMD [“/usr/sbin/httpd”, “-D”, “FOREGROUND”]

Instructions in Dockerfile

The syntax of Dockerfile is simple and contains below instructions:

FROM:

FROM is the first instruction in any Dockerfile and it defines the base image to use. Base image can be any existing Docker image, typically it is operating system image or a specific application framework.

Usage:

FROM <image>

FROM <image>:<tag>

MAINTAINER: [deprecated]

It is used to set the author of that image. You can do same task using LABEL instruction.

Usage:

MAINTAINER <name>

RUN:

RUN is used to run or execute commands in the container. Usage of RUN is RUN <command> , command is run in a shell, which is by default /bin/sh –c

Usage:

RUN <command> (shell form, the command is run in a shell, which by default is /bin/sh –c)

ADD:

ADD is used to copy the files, directories, remote file URLs from current directory into the container. Eg ADD <src><dest>.

<src> file can also be tar archive, the same will be unpacked for you as a directory into the docker image.

If <dest> path do not exist, it will be created for you.

Usage:

ADD <src><dest>

COPY:

It is similar to ADD, but it do not support the compression and URL file functionality. It is used to copy the files or directories from <src> and adds them to the destination path.

Usage:

COPY <source>… <destination>

CMD:

When container starts up, these commands will be executed/run. It is used to provide defaults for an executing container. The defaults can be executables or in case executable is omitted/excluded then you must specify an ENTRYPOINT instruction as well. In case there are more than one CMD in the dockerfile, then only the last CMD will take effect.

In case a user specify any arguments to docker run, then they will override the defaults mentioned in CMD.

Usage :

CMD [“executable”,”param1″,”param2″] (exec form)

CMD [“param1″,”param2”] (default parameters to ENTRYPOINT)

LABEL:

It is used to add metadata to an image. A label is a key-value pair. An image can have more than one label. You can view image labels using docker inspect command.

Eg of Label:

LABEL version=”1.0″

EXPOSE:

It is used to inform Docker that container listens on the specified network port at the runtime. You can specify the protocol as well (TCP or UDP), by default TCP is the protocol if nothing is specified.

Using EXPOSE, the ports are exposed and can be used to publish and map one or more ports using –p option with docker run.

Regardless, of the EXPOSE instruction, the settings can be override at runtime by using the –p flag.

For eg.

docker run –p 80:80/tcp –p 5050:5050 ….

Usage:

EXPOSE <port> [<port>/<protocol>…]

ENV:

The ENV instruction is used to set the environment variable <key> to the value <value>

First format given in usage below will set single variable to value, while the second format can be used to set multiple variables at one time. You can view all the set environment variables using docker inspect command and change them using dockerrun –env<key>=<value>

Usage:

ENV <key><value>

ENV <key>=<value> …

ENTRYPOINT:

ENTRYPOINT allows you to configure a container that will run as an executable.

What’s the difference between CMD and ENTRYPOINT

Docker has default entrypoint (/bin/sh -c) but does not have a command. For example, running below <docker run image>, here the default Entrypoint will be /bin/sh -c and CMD will be bash. So that means, CMD is run via the ENTRYPOINT or CMD will be the parameter of the entrypoint.

Docker run –i –t ubuntu bash
Entrypoint : /bin/sh –c
Cmd : bash

Another example, suppose you want to use ENTRYPOINT as /bin/cat. So, when docker run image /etc/passwd command will run /etc/passwd is command and it is passed to the ENTRYPOINT /bin/cat and the execution is /bin/vat /etc/passwdd

Final Conclusion is ENTRYPOINT specifies a command that will always be executed when container starts.

CMD specifies arguments that will be fed to the ENTRYPOINT

Usage:

ENTRYPOINT [“executable”, “param1”, “param2”] (exec form, preferred)
ENTRYPOINT command param1 param2 (shell form)

VOLUME:

Volume defines a path or creates a mount point in the container that Docker exposes to the host system and it can be mapped using the -v option.

The docker run command initializes the specified volume along with the existing data in the volume within the base image.

Usage:

VOLUME [“/path”]

VOLUME /path1 /path2 ..

USER:

USER instruction sets the username or UID to use while running the image. Also, GID or user group can also be specified with USER instructions.

Usage:

USER <user>[:<group>]

USER <UID>[:<GID>]

WORKDIR:

The WORKDIR instruction is used to set the working directory for any ADD, COPY, CMD, RUN or ENTRYPOINT instruction that follows it. It can be used multiple times in a Dockerfile.

Usage:

WORKDIR </path>

ARG:

ARG instruction is used to define a variable that can be passed at build time to the builder docker build using the –build-arg <variable>=<value>

A dockerfile can contain multiple ARG instructions. Environment variable defined using ENV instruction always override the ARG instruction.

It is not recommended to pass user credentials, github keys as build time variables as the same will be visible in docker history command.

Usage:

ARG <name>[=<default value>]

SHELL:

SHELL instruction is particulary useful for Windows and it allows to override the default shell (/bin/sh -c) for Linux and (“cmd” “/S”, “/C” ).

SHELL instruction also allows to use alternate shells like zsh, tsh, powershell etc.

Usage:

SHELL [“<executable>”, “<param1>”, “<param2>”]

Please comment down your thoughts on Dockerfiles and let us know if you have any query.

How to Change Hostname in Linux (CentOS 7.x/RHEL 7.x)

2019-11-28T16:26:00.000+05:30

How to Change Hostname in a Linux Machine using hostnamectl command

Introduction

This article is about how you can change your Linux machine hostname using the hostnamectl command. While installing Redhat 7.x or CentOS 7.x, in case you have not specified any hostname, then by default “localhost.localdomain” will be assigned as default hostname for that machine. You can easily change the hostname for your Redhat or CentOS Linux machine using the hostnamectl command. This method can be used for CentOS 7.x / RHEL 7.x and RHEL 8 operating systems.

Method 1: hostnamectl

hostnamectl command can be used to change or query system hostname and related settings. The advantage of using hostnamectl is that , we dont require machine reboot to make the changes. Let us learn more about hostnamectl command.

Types of Hostnames

Pretty Hostname: The high level pretty hostname is in the form of Human readable format and it can include all kinds of special characters. Example of Pretty hostname can be “John’s Laptop” or “Database Server”.
Static Hostname: It is the traditional hostname, which can be chosen by the user and used to initialize kernel hostname at boot. It is stored in the /etc/hostname file.
Transient Hostname: It is the dynamic hostname maintained by the kernel and is initialized to the static hostname by default.

Changing your Hostname in CentOS 7 or RHEL 7 /RHEL 8

In CentOS and RHEL 7.x onwards hostname query and control is managed by hostnamectl command. You can use hostnamectl command to change or set hostnames. As described above, all the three hostnames viz Pretty hostname, static hostname and transient hostname can be set using hostnamectl.

To view all the Host names

To query about current status of hostname information, issue the hostnamectl command.

# hostnamectl

To change all the Hostnames

To change all the host names command, use below command as root user. This will change the pretty, static and transient hostnames alike.

# hostnamectl set-hostname name

To Set a Particular hostname

In case you want to set a Particular hostname, use below command with required option.

# hostnamectl set-hostname name <options>

Options can be either:

–static
–pretty
–transient

Example of setting Pretty hostname:

# hostnamectl set-hostname "John's Laptop" --pretty

Example of setting Static hostname:

# hostnamectl set-hostname linuxforgeek --static

To clear a particular hostname

Use below command as root user to clear a particular hostname and revert the same to its default.

# hostnamectl set-hostname "" <options>

In above command “” refers to empty string and will clear the hostname and <option> can be either –pretty, –static or –transient.

Making new hostname effective

Once you are done with changing the hostname of your Linux server/machine, you can open up a new terminal session or issue shell command bash to update in the current session

# bash

Method 2 : modify /etc/hostname

Another method to change hostname in RHEL 7.x/CentOS 7.x is by changing hostname in /etc/hostname file followed by the reboot.

# vi /etc/hostname
# reboot

That is all for this post, feel free to comment below for any query.

How to add a user to group in Linux

2019-11-28T16:13:00.000+05:30

This post will help you to understand how you can add a user to a group in Linux. Though it is a very simple task, if you have any confusion regarding it, this guide will clear all your doubts.

There are two ways of adding a user to a group. You can use the useradd or usermod commands for doing this task.

useradd: It is used to create a new user as well as it can be used to update the default new user information.
usermod: It is used to modify a user account. This can be used to add a user to existing group.

Talking about groups, there are two types of groups in Linux

Primary Group: It is the group applied when user login using any method(ssh, tty, GUI) etc. Typically it is same as the login name.
Secondary Group: These are the supplementary groups which the user is also a member of.

Now, let us see the commands used to add a user to a Group.

Add a new User Account to a Group

Below example will create a new user john with sales group as his primary group and mktg, hrd as his secondary group. Ensure that primary and secondary groups exist in the system before running this command

# useradd -g sales -G mktg, hrd john

To add a new user Kumar with primary group Engineering

# useradd -g Engineering Kumar

Add an existing User Account to a Group

If you already have a user and you want to add the same to an existing group on your Linux machine, we will use usermod command.

Assign Secondary Group to an existing user

Let us suppose if you have an existing user david and you want to add the same to a secondary group webmasters, you can use below command.

# usermod -a -G webmasters david

You can check and verify the same by id command, as explained in the example above, user david has been added to secondary group webmasters.

Assign Primary Group to an existing user

Also, each user has primary group assigned to it like user david has primary group david. If you want to change the primary group of user david as web-admin, then run below command. For changing primary group (-g) option will be used with usermod command.

#  usermod -g web-admin david

To list all the users belonging to a particular group, we can use lid command.

linuxforgeek:~# lid -g webmasters
 david(uid=3028)
 john(uid=3029)
 kumar(uid=3030)
 jack(uid=3031)

To list all the groups of a particular user use groups command.

linuxforgeek:~# groups david
david : web-admin webmasters sudo

40 examples of find command in Linux

2019-11-28T16:08:00.002+05:30

Hello Geeks, In this post, we will learn about find command that is one of the important command in Linux. It can help you find anything you want to search in our machine.

In Linux, everything is in the form of files and find command can be used with a lot of options like name, permissions, modification/accessed time, matching string, finding a particular format file. Using the relevant option with find command can ease the task and you will get the results quickly.

find command is available on all the flavors of Linux. In this tutorial, we will learn examples of find command that a Linux System administrator or a Linux User should know.

Basic Syntax of find command

# find <path> <selection criteria> <action>

Search Files using Name

1. List all the files in the current directory and sub-directories

Using find without any option will list all the files in the current directory and sub-directories.

# find 
or
# find .

2. List all the files in any specific diectory

This will show all the files in that particular path specified after find.

# find /<path>

3. Find all the files of your present working directory

To list all the files (not directories) in pwd use below command

# find . -type f

4. Find all the directories in your present working directory

This option will help you find all the directories in your pwd

# find . -type d

5. Find files using name in Current Directory

If you want to search for a file of a particular name. For example, to find “new.php” file in the current directory and sub-directories

# find . -name "new.php"

6. Find files using the name in a specific directory

Specify the path after find to search in that particular directory.

# find /boot -name grub.cfg

7. Find file(s) in multiple directories

You can give multiple directories in the path.

# find /boot /etc -name grub

8. Find file using name and ignoring case

It will show both lowercase and uppercase results, hence ignoring the case.

# find <path> -iname <file or directory>

9. Find Directory using name

Specify the name of directory to be searched after -name

# find / -type d  -name LinuxforGeek

10. Find files with particular extension/format

This is very useful thing, in case you want to search for any particular file format example shell scripts ends with .sh, music formats are in .mp3, text files are in .txt

# find / -name "*.php"

11. Using maxdepth for limiting the search to a specific directory

In case you want to skip huge trees of sub directories and limit your search to one or two depth.

# find /<path> -maxdepth 2 -name "search pattern"

12. Find all the files other than mentioned type / Invert match

It will show all the results except the specified in selection criteria section.

# find /test -not -name *.php"
or
# find ./test ! -name "*.php"

13. Using combination of search criteria

It is possible to combine two search criteria by specifying name and including invert match as shown in below example.

# find /test -name 'abc*' -not -name '*.php' -not -name "*.sh"

14. Using OR condition in find command

# find / -name "abc.txt" -o -name "linuxforgeek.txt"

15. Search File names matching regular expression pattern

# find /test  -regex ".*\.\(txt\|php\)$"

16. Find all hidden files

# find ~ -type f -name ".*"

Finding files based on Permissions, owner or group

17. Finding files with permissions

# find /test -type f -perm 0777

18. Finding files that not having 777 permissions

# find /test -type f -not -perm 0777
or 
# find /test -type f ! -perm 0777

19. Find files with suid bit set

find /usr -perm /u=s

20. Find files with sgid bit set

# find /usr -perm /g=s

21. Find files with sgid bit set and 755 permissions

# find / -perm 2755

22. Find files with sticky bit set and 755 permissions

# find / -perm 1755

23. Find read only files

# find / -perm /u=r

24. Find all the executables files

# find /test -perm /a=x

25. Find all the files owned by a user

# find / -user john

26. Find all the files owned by a group

# find / -group dba

Finding files based on modification date and time

27. Find files modified 10 days back

# find / mtime 10

28. Find files accessed in last 10 days

# find /-atime 10

29. Find files modified between 5 to 20 days

# find /-mtime +5 -mtime -20

30. Find files changed in last one hour

# find / -cmin -60

31. Files modified in last one hour

# find / -mmin 60

32. Files accessed in last one hour

# find / -amin 60

Finding files based on size

33. Finding file of a particular size

# find / -size 20M

34. Finding files between size range

# find / -size +10M -size -50M

35. Finding smallest and largest file

# find / -type f -exec ls -s {} \; | sort -n -r | head -5

36. Find empty files

find /tmp -type f -empty

37. Find empty directories

# find /tmp -type d -empty

Advanced operations: Performing action on the find output

38. List all the found files

You can easily list files of any size using find command. Below example lists the files of larger than 100 MB

# find . -size +100M -exec ls -lrth {} \;

39. Find specific Files and Delete

Below example can be used to find all the mp3 files of greater than 10 MB and execute part will remove(delete) the same.

# find / -type f -name *.mp3 -size +10M -exec rm -rf {} \;

40. Find files with specific permissions and chmod (change permissions) to 755

Below command can be used to find all the files with 644 permissions and the action part is to execute “chmod 755” on all the files found.

# find / -type f -perm 644 -print -exec chmod 755 {} \;

That’s all for this tutorial, Hope you have understood find command usage with given practical examples.

Using Stratis to configure local storage in RHEL 8 and Fedora

2019-11-28T16:04:00.002+05:30

What is Stratis ?

One of the new features intoduced in RHEL 8 is the new Local Storage Management tool Stratis. Stratis is a hybrid user-and-kernel local storage management solution that simplifies and eases the task of Initial Configuration of Storage, making changes in the existing configurations such as expansions of volumes/file systems and offers advanced storage features like thin provisioning, pool based management, managing snapshots, tiering and monitoring.

Stratis: Volume-Managing File System(VMF)

Startis is not a traditional file system like ext4, xfs but it is a Volume-Managing filesystem like ZFS and Btrfs. Stratis is based upon the concept of storage pool. The pool is created from one or more local disks or partitions and further volumes are created from the pool. The concept of Pool is common to Linux Volume Manager(LVM).

Components of Stratis Volume

Stratis Volume consists of following components:

blockdev: It is the block device such as local disk or disk partitions.
pool: pool is created from one or more block devices or disk partitions. Size of the pool is equal to the size of total block devices. For each pool, Stratis creates a directory as /Stratis/pool-name
filesystem: From the storage pool, we can create one or more file systems that can be mounted on the system and stores files. File systems are configured as thin provisioned and its size increases with the data stored on it. XFS is the default File system used by Stratis. Filesystems are created in /stratis/pool-name/file-system-name

Supported Storage Devices by Stratis

Below storage devices can be used for Stratis.

LVM Logical Volumes
iSCSI
mdraid
Device Mapper Multipath
LUKS
SSD
NVM storage devices
hard drives

Software Component

Stratis consists of two software components:

Stratis CLI : Command line interface converts the commands into D-bus API calls to stratisd
Stratis Service – stratisd implements the D-bus interface and monitors and manages the Stratis internal pool

Installation of Stratis

RHEL 8 is distributed with Stratis software components mentioned above. To install Stratis on your system use dnf or yum. DNF (dandified yum) is the latest package manager distributed in RHEL 8.

# dnf install stratisd stratis-cli

Make sure that stratisd service is enabled at boot. Use below command for enabling.

# systemctl enable --now stratisd

Creating a Stratis Pool

For this demo, I have exposed three disks of 1 GB each as shown below. Before creating pool make sure stratis daemon is running and block device used for pool should be at least 1 GB each in size.

Three disks/ block device used for pool creation are as below:

sdb             8:16   0    1G  0 disk 
sdc             8:32   0    1G  0 disk 
sdd             8:48   0    1G  0 disk

In case, your disk or block device contains partition table or file system, erase them using below command.

# wipefs -a /<devicepath>

Creating Pool 1 using one disk /dev/sdb

# stratis pool create pool1 /dev/sdb

Now, lets create pool2 that will use two disks /dev/sdc and /dev/sdd

# stratis pool create pool2 /dev/sdc /dev/sdd

To list the pools, use below command. As clear from the output we have created two pools of 1 GB and 2 GB respectively.

[root@rhel8beta ~]# stratis pool list
Name     Total Physical Size  Total Physical Used
pool1                  1 GiB               52 MiB
pool2                  2 GiB               56 MiB
[root@rhel8beta ~]#

Creating a Stratis File System

Now we have two pools ready, out of which we can create a Stratis file system.

# stratis fs create <my-pool> <fs-name>

From pool1, let us create file system 1 named app and using pool2, let us create another file system named database as shown in screenshots below.

To list File systems, run below command.

# stratis fs list

Mounting a Stratis file system

To mount the file system, use the entries that stratis maintains in directory /dev/stratis

# mkdir -p /app
# mount /dev/stratis/pool1/app /app

# mkdir -p /database
# mount /dev/stratis/pool2/database /database

Once mounted, you can check the same using “df” command as shown below. You will notice that new file systems show up as 1 TB, Stratis file systems are formatted with XFS but maintained on behalf of user. They show up in df as the virtual size of the XFS file system and actual usage is less due to thin provisioning.

To make the mount point persistent, add the entry of the same in /etc/fstab file.

You have learned about Stratis, how to install the same and use Stratis to manage local storage on RHEL 8 or Fedora Linux.

How to install Packages using dnf on RHEL 8

2019-11-28T15:59:00.001+05:30

In our previous post, we have discussed about the installation of RHEL 8 beta that has been released for developers and testers. RHEL 8 has a lot of new features, you can check all the major new features here, Talking about Package and software management, RHEL 8 has introduced an advanced and new version of yum that is known as dnf (dandified yum) that offers several advantages like increase in performance, support for modular content is added and has well-designed API for integration with tooling.

DNF is the new upcoming major version of YUM that is used for package management of rhel 7.x based systems. DNF was introduced in Fedora 18 and it is now available in RHEL 8 for managing rpm based packages.

To Search a Package with dnf

To search a Package using dnf use below command. For example to search for nginx that is now available in the base OS repository of RHEL 8

# dnf search nginx

Install a Package with dnf

To install a Package using dnf command, run dnf install followed by the package name, it works similar to yum. You can use -y at the end if you dont want to get the prompt for confirmation. All the dependencies required for the package will be automatically resolved.

# dnf install nginx

Removing a Package with dnf

To remove the installed Package along with its dependencies, run the below command.

# dnf remove nginx

Get info of a Package with dnf

You can get information about a Package using dnf that gives the details about Package like name, version, Arch, Size, repo, URL, license and description.

# dnf info firefox

Check if Update for any Package is available

You can check if any update for any specific package is available using the check-update option, if no package is specified, it will check whether any updates for the system is available.

# dnf check-update <package-specs>

Update Packages with dnf

You can use dnf upgrade to update the package to the latest version available. It also takes care of dependencies as required. In case there is no update available, it will show the message “Nothing to do”

# dnf upgrade <package>

List all the available repositories

using dnf repolist, you can list all the enabled as well as disabled repositories.

# dnf repolist all

Clean dnf cache

Clean performs the cleanup of temporary files kept for repositories. To clean all the cached files from the enabled repositories, run below command regularly to clean up the cache.

# dnf clean all

Group Packages

Group is collection of packages. To install, remove or upgrade group package use options as shown below.

To List all the matching groups

# dnf group list <group-spec>

To install a Group Package

# dnf group install <group-spec>

To remove a Group Package

# dnf group remove <group-spec>

To Display package lists of a Group

# dnf group info <group-spec>

To Upgrade the Group packages

# dnf group upgrade <group-spec>

View History of dnf

To view all the past transactions of dnf, use below command.

# dnf history

You can perform various operations with dnf history like redo, rollback, undo.

# dnf history redo <transaction-spec>
# dnf history rollback <transaction-spec>
# dnf history undo <transaction-spec>

To know what package provides a File

Provides command is useful to find out the package providing a file. In case you know a filename and what to know what package provides that file, use below file.

# dnf provides <provide-spec>

Open an Interactive dnf shell

You can open an interactive dnf shell to conduct multiple commands during a single execution of DNF.

# dnf shell

40 Linux Commands for Beginners and intermediate users

2019-11-28T15:52:00.001+05:30

Linux is the most popular Operating System when it comes to Servers world, with around 90% of the internet running on Linux.

In this Post, we will list the basic 40 commands that a new Linux user or a Linux System Administrator should be aware of. These commands are used in day to day activities while working on Linux Servers. Note that Linux commands are case sensitive.

Starting with the basic ones.

1. pwd

pwd stands for print working directory, pwd displays the complete path of the current directory from / (root) of the file system.

Basic Syntax of pwd

# pwd

2. mkdir

mkdir command is used to create one or more directories. It is important to note that a user executing mkdir command must have enough permissions for execution, else it will display “permission denied” error.

You can use following options with mkdir

-p or –parents : creates parent directory as needed.

-v or –verbose : displays message for every directory created.

Basic Syntax of mkdir

# mkdir <options> <directory name>

3. cd

You can use cd command to change or switch to a specific directory.

Basic Syntax of cd

# cd <directory name>

cd ..	Used to change current directory to parent directory
cd ~	Change directory to user home directory from anywhere
cd –	Switch to previous directory where you were working last
cd —	Shows last working directory from where we have moved to current path.

4. touch

touch command is used to create empty files. Using touch command, you can also modify the last modification time and other file attributes

You can use below options with touch command

-a : Changes only the access time

-m : Changes only the modification time

Basic Syntax of touch command

# touch <options> <filename>

5. cat

cat command is used to see the contents of a file. cat command can be used to create new files, overwrite existing file and append something to existing files.

Basic Syntax of cat command

# cat [filename]     To see the contents of the file
# cat > [filename]   To create or overwrite a file
# cat >> [filename]  To create or append to a file

6. file

file command displays the file type of a particular file. In Unix, everything is a file whether it is a directory, normal file, device file, socket file etc

Basic syntax of file command

# file <filename>

7. ls

ls command is used to list the files and directories.

Basic syntax of ls command

# ls <options>

Some common options that can be used with ls command:

ls -a : Lists all the files that includes files, directories, hidden files, current directory link (.) and parent directory link (..)

ls -i : prints the inode no of each file

ls -l : lists files and directories in long format.

ls -r : lists the file in reverse or descending order

ls -h : print size of the file in human readable format

8. rmdir

rmdir command is used to remove the directory or complete directory structure.

Note that : rmdir command only removes the empty directories.

Basic Syntax of rmdir

# rmdir <directory name>

9. rm

rm command is used to remove files, directories, symbolic links or any other object from the system.

Basic Syntax of rm command

# rm <options> <file or directory name>

Options:

rm -i : interactive mode, asks for confirmation before removing any file.

rm -f : forcefully deletion, removes the file forcefully.

rm -r : recursively removes directory and its contents

rm -v : displays the verbose message.

10. cp

cp command is used to copy the files or directories from one location to another. Without mentioning any option with cp command, it can copy only files, for copying the directories -r option is used.

Basic Syntax of cp

# cp <options> <source>  <destination>

Options:

-i : interactive mode, asks for confirmation before writing.

-r and -R : recursively copies the directory structure

-f : force copy

-v : displays the verbose message

11. mv

mv command is used to move the files or directories from one location to another.

Syntax of mv

# mv <source> <destination>

Options:

-i : interactive – asks for confirmation before moving.

-v : verbose

12. more

more command is used to navigate or see the contents of a file or output of a command. Using more command, you cannot scroll backward.

Basic Syntax of more command

# more <filename>
# command | more

13. less

less command is also used to see the contents of a file or output of commands page-wise or line-wise. Advantage of less command is that you can scroll back and forth.

Basic Syntax of less command

# less <filename>
# command | less

14. head

head command be default displays the first 10 lines of a file. Also you can specify the number of lines you want to see with head command.

Basic Syntax of head command

# head <options> <filename>

Options:

-n : Prints the first n number of lines eg. head -n 20 filename.txt

-c : Prints the number of bytes specified with -c option eg. head -c 15 filename.txt

15. tail

tail command by default displays last 10 lines of a file. If you want to see any custom number of lines, use the -n option followed by number of lines and file name. tail is often used to see the logs file.

Basic syntax of tail command

# tail <options> <filename>

Options:

-n : To see any number of lines.

tail -f /var/log/messages : To watch the system logs

16. man

man command is used to see the manual pages for all the command that contains all the options, usage for that command.

Basic Syntax of man command

# man <command>

17. history

history command keeps a list of all the commands that have been run/executed on the system

Basic syntax of history command

# history

Options:

to search for a particular text pattern use grep

history | grep <text_pattern>

history -c : Clears the history

18. cal

cal command displays the calendar, you can choose following options with cal command.

Basic Syntax of cal

cal

Options:

cal 12 2018 : Displays selected month and year on the console

cal 21 12 2018 : Display the day, month and year calendar on console, also highlights the day.

cal -1 : Displays the calendar of current month

cal -m : Displays monday as the first day of the week

19. date

date command is used to view or set date and time of the Linux system.

Basic Syntax of date

# date

20. su

su command is used to temporarily change to a different user that means to switch from one account to another. User will be prompted to enter password while running su command.

Basic syntax of su command

# su - <username>

21. echo

echo command is used to display a line of text or strings on the screen or append the file with text. echo is generally used in shell scripts for displaying any message.

Basic Syntax of echo

# echo <options> <strings>

Options

-e : enable back slash escape character for escape characters like \\, \a,\n, \t, \v

echo *.tar : will print all the files ending with .tar extension

echo “Hi, Welcome to linuxforgeek” >welcomepage [can be used as redirect operator]

22. uptime

uptime command is quite common and it is used to check the system’s uptime that means the date and time since the system is up. It also gives additional information like load average of cpu since 1, 5 and 15 minutes and number of users logged into the system.

Syntax

# uptime

23. clear

clear command is used to clear the screen

Syntax

# clear

24. hostname

hostname command displays the hostname or machine name configured for the system.

Syntax

# hostname

25. id

id command is used to print the username, uid, gid and groups of the user. For checking a specific user information use id <user>

Syntax

# id

26. who

who command displays following information:

Users who are connected

terminal to which they are connected

date and time since they are logged in

remote hostname of the user

Syntax of who command

# who

27. w

w command display more information than who command and you ay want to use w instead, it display the logged into the Linux and what are they doing that means current running process.

Syntax of w

# w

28. whoami

if you want to know which user you are currently logged in. The output of whoami shows the current user.

Syntax

# whomai

29. whatis

whatis command is used to know one line or brief description of Linux commands.

example :$ whatis top will show short one liner description about top

Syntax

# whatis <keyword>

30. which

which command gives the complete absolute path of a particular command.

Syntax

# which <command>

31. wc

wc command can be used to display the bytes, lines, and characters of a file.

Syntax

# wc <options> <filename>

Options

-l : print the lines count.

-w : prints the word count.

-c : prints the bytes count.

-m : prints the character count.

32. ln

ln command is used to create softlink or hardlink. links are references or alias to the same file with different name.

Syntax

# ln <options> <source> <destination>

33. alias

alias command is used to display all the configured aliases on the system, also it can be used to set aliases.

Syntax

# alias <arguments>

eg. alias cl=’clear’

If you want to make the alias permanent, you need to add the same in your ~/.bashrc file.

34. unalias

If you want to remove the alias from the system, use unalias command.

Syntax

# unalias <alias>

35. uname

uname command displays the system information. It can be used with various options.

Syntax

# uname <option>

Options:

-a : all information

-s : Kernel name

-m : machine type

-n : nodename

-p : prints the processor type

-o : operating system

-r : kernel version

36. uniq

uniq command in linux is used to remove the duplicate lines or filters repeated lines in a file

Syntax

 # uniq <options> <filename>

Options:

-c : counts the number of occurrences or how many times a line is repeated

-d : only prints duplicate lines

-i : ignore case sensitivity

37. sort

sort command is used to sort the contents of a file in ascending or descending order. In case no option is specified, sorting is done in ascending order.

Syntax

# sort <options> <filename>

Options:

-r : to sort in descending order.

-n : to sort a file numerically

38. find

find command is one of the powerful tool in Linux. It can be used to recursively look for files matching selection criteria.

Syntax

# find <path> <selection criteria>  <action>

<path> : You can specify the absolute or relative path where you want to find the files. example /var , /etc/ or /

<selection criteria> : Following are the selection criteria that can be used with find command.

-atime <n>: file accessed last <n> days ago

-ctime <n>: file who attributes are changed last <n> days ago

-mtime <n>: modified <n> days ago

-type <x> : to filter type of file. It can be following

f : ordinary files

d : directory

l : symbolic links

s : socket files

p : named pipes

c : character device files

b : block device files

-links (n) : find the files having n number of hard links

-user (uid) : find the files that are owned by a specific uid/username

-group (gid) : find the files that are owned by a specific gid/groupname

-name (filename) : find the files with its name.

-perm : to search using specific permissions

<action> : Following action can be used with find

ls : for listing files

-print :to print output on the screen

-exec <cmd> {}\; To execute command <cmd> on the output.

39. grep

grep command is used to search for a specified string pattern in the files or output of commands.

Syntax

# grep <options> <string pattern> <filename/command>

40. ping

You can use ping command to check connectivity with a particular server or IP address.

example :ping google.com will check connection to google.com

Syntax

# ping <IP or hostname>

We hope you liked this tutorial, keep visiting linuxforgeek.com for more interesting tutorial, Please feel free to comment below.

RHEL 8 new features

2019-11-28T15:48:00.000+05:30

What’s new in RHEL 8

Red Hat Enterprise Linux 8 or RHEL 8 beta version has been released for developers and testers. You can check our previous post regarding installation of beta release of RHEL 8.

Let us see high level view of some of the new features that are introduced in RHEL 8.

Kernel

RHEL 8 is running on kernel version 4.18 and based on Fedora 28. Control Group V2 is supported that manages and distributes system resources in a better way compared to the previous version. Control group v2 has only single hierarchy that categorizes processes based on the role of the owner thereby removes the conflicts policies arising due to multiple hierarchies.

Enhancement in sosreport and kdump is also done. RHEL 8 now supports early kdump compared to previous versions in which kdump was not able to capture crash information early. eBPF based programs and maps can be reported using sosreport.

Support for 5-level paging now enables RHEL 8 to supports upto 4 PB of physical memory. Earlier version RHEL 7 has 4 level paging that allows addressing space of 256 TiB, same has been increased to 128 PiB and thus increasing physical address space up to 4 Pib

Software Management

RHEL 8 offers improvement for package management tool yum, which is now based on DNF (Dandified Yum) technology that is advanced and has better performance with support for modular content. RPM version 4.14 is distributed in RHEL 8 and rpm now validates the package content before starting the installation. Support for packaging files above 4GB in size is added.

dnf utility allows to install, upgrade packages.

# dnf install  
# dnf update
# dnf upgrade
# dnf provides

File Systems and storage

XFS file system supports shared copy-on-write data extent functionality that allows sharing a common set of data block for two or more files that is Fast and space efficient. LUKS2 replaces the legacy LUKS1 format. LUKS2 provides encrypted volumes that supports auto recovery in case of metadata corruptions.

Stratis is new local storage manager that provides managed file systems on top of pools of storage that simplifies tasks like Managing snapshots, expanding file systems on the fly, XFS is default file system used by stratis.

Cockpit

RHEL 8 is having pre-installed cockpit packages on non minimal installations as well as firewall ports are opened, Package can be obtained from RHEL default repositories for minimal installations. Cockpit’s web interface can be used for managing machines remotely easily.

Cockpit is now compatible with mobile browsers, thus managing systems using mobile devices is possible now. Cockpit’s page now warns and informs about missing updates and subscriptions. Cockpit interface can also be used to apply Policy-based Decryption rules to disks on the systems.

Virtual Machines can now be created and managed using Cockpit. Another enhancement is that Networking page allows modification of firewall rules.

Replacement of nfsnobody user with nobody

nfsnobody and nobody user of RHEL 7 with ID of 65534 and 99 respectively have been merged as single user nobody with ID 65534 and RHEL 8 installation no more creates nfsnobody user.

Databases, webservers, languages

Databases Servers in RHEL 8: MySQL 8.0, MariaDB 10.3, PostgreSQL 9.6 and PostgreSQL 10, Redis 4
Python 3 .6 is distributed on RHEL 8
Ruby 2.5
PHP 7.2
Perl 5.26
Apache HTTP Server 2.4.35
RHEL 8 comes with nginx 1.14 available in the base repository

Desktop

RHEL 8 Desktop Environment has been rebased to GNOME 3.28 that include new features like on screen keyboard, extended device support. Wayland replaces the X.org of previous RHEL release and is the default display server in RHEL 8 that offers advantages like improved multi-monitor support, enhanced UI scaling,

Networking

iptables has been replaced with nftables as default packet filtering framework which is the successor to iptables, arptables, and ebtables tool.

nftables has several advantages like it offers single framework for ipv4 and ipv6 protocols packet filtering. Another utility nftrace is provided that helps in debugging and tracing in the ruleset.

TCP Networking Stack version 4.16 is distributed on RHEL 8 that provides more stability and better performance.

By Default, firewalld uses nftables

Virtualization

Bunch of new features are added like KVM supports 5-level paging, additional crash information in case KVM guest crashes, Ceph storage is now supported as well on KVM

RHEL 8 is distributed with qemu–kvm 2.12 with new features like support for Q35 guest machine type, UEFI guest boot, vCPU hot plug/unplug, Guest I/O threading.

Security

The openssh package have been upgraded to version 7.8p1 that removes support for ssh version 1 protocol, Enhancement in rsyslog is also there with upgraded rsylog version 8.37.0

Containers without daemons

RHEL 8 comes with Podman and buildah aka CRI-O that is alternative to dockers and can be used to manage containers.

What is /etc/shadow file and various fields in /etc/shadow

2019-11-28T15:42:00.001+05:30

After understanding /etc/passwd file in previous post, let us understand another important configuration file related to user management i.e /etc/shadow. As earlier explained in the /etc/passwd file that second field written as (x), means shadowing is enabled and encrypted password exists for that user in another file “/etc/shadow”. Encrypted passwords can be stored in /etc/passwd file but that is not recommended as there is security risk due to world readable permissions on the /etc/passwd, that is why it is a good practice to have encrypted passwords stored in separate /etc/shadow file.

One-Liner Definition:

/etc/shadow file stores the encrypted password and other passwords related information and policies like expiration etc for the user’s accounts.

Contents of /etc/shadow file

Below is the format of /etc/shadow file.

Fig: /etc/shadow fields

Following are the different fields of /etc/shadow file.

Username or Login name: First field of /etc/shadow file is the username or login name. In the above example, John is our username.
Encrypted Password Hash: Second field of /etc/shadow file contains the encrypted password. For encryption, SHA512 algorithm is used. A blank entry (::) means no password is required to login for that user, while a (*) entry means that account of that user has been disabled.
Last Password Change: Third fields give the number of days since January 1, 1970, that last password was changed.
Minimum number of days between password change: Minimum number of days you must keep a password. (0 in the fourth field means password can be changed anytime)
Maximum number of days password is valid: Maximum number of days password is valid and after which password expires and the user is forced to change the password.
Warning: Number of days before password expiration, the warning message will be given to user regarding an expiring password.
Account Disabled: The seventh field specifies the number of days after the password expiration, the account will be disabled, Once the given days in this field are elapsed, the account will be inactive/disabled.
Account expiration duration in days since epoch: Number of days since January 1, 1970 since the account has been disabled.
Not used or reserved for future use.

What is Shadowing ?

Earlier the passwords of users were stored in encrypted format in second field of /etc/passwd. Since /etc/passwd file is world readable that means any user can see the contents of it, so there is security risk. To overcome this problem, passwords were kept in a separate file /etc/shadow along with other password related information.

By default, shadowing is enabled on Linux System. To disable shadowing use #pwunconv command and to enable it back use #pwconv command.

Sample /etc/shadow file looks like:

Permissions on /etc/shadow file

---------- 1 root root 1144 Aug 16 15:41 /etc/shadow

Earlier versions of RHEL have 600 permissions on /etc/shadow. Above are the permissions (000) of /etc/shadow file on a RHEL 7 machine, Normal users can not read this file, it is owned by user root and group root, hence file is only accessible to root user, If you try to modify this file as root, you will get a warning ” You are trying to modify a read-only file”

That’s all for this tutorial, i hope you must have understood /etc/shadow file if you have any doubts or questions, feel free to comment below.

Boot Process in Linux

2019-11-28T15:36:00.001+05:30

Hello Geeks, Boot Process in Linux is very important topic and a Linux System administrator must know all the steps in the boot process to fix and troubleshoot boot issues.

From powering on the machine till the time we get the login prompt, it goes through several steps. Below info-graphic shows the high-level steps during the boot process.

High Level Steps of Boot Process in Linux

Now let us see all the steps of boot process in detail

BIOS

Basic Input/Output System or simply BIOS is the first stage of the boot process. BIOS is stored in the ROM of the motherboard of the system and it is always executed regardless of the operating system installed. BIOS performs the POST – Power-on self-test to detect, initializes and test the connected hardware. POST ensures that all the connected hardware is working fine. Once done with the POST part, next task that BIOS does is to determine the bootable device like cd-rom, hard-disk, USB drive etc. Once BIOS finds a valid bootloader device, it gives control to the first sector of the bootable device or simply loads the master boot record (MBR).

Master Boot record:

MBR is the first sector of bootable device and it is of 512 bytes. 512 bytes of MBR are divided into three parts.

446 bytes of bootloader that is knows as GRUB, 64 bytes contains the partition table info and 2 bytes for MBR Validation check used for error detection. MBR loads the GRUB2 boot loader into memory and transfers control to it.

GRUB2 bootloader

GRUB2 is default bootloader used from RHEL 7 onwards, replacing the legacy grub of earlier versions. GRUB stands for Grand Unified Boot Loader

Grub menu during boot process

Grub 2 configuration file is located at /boot/grub2/grub.cfg and it takes menu configuration settings from another file that is /etc/default/grub

/boot/grub2/grub.cfg  < Config file >
/etc/default/grub  < Menu Configuration settings >

GRUB2 searches for the compressed kernel image “vmlinuz” in the /boot directory and loads the “vmlinuz” content into memory and extracts the content of initramfs image into a temporary file system (tmpfs)

Kernel

The function of kernel is to handle and control all the Operating system processes and like memory management, input output devices, task scheduling. Kernel starts the first process that is systemd with pid of 1.

You can check using top command or ps -ef | grep systemd

   1 root      20   0   51788   3912   2496 S   0.0  0.0   5:06.62 systemd

Initrd or initial RAM disk is used to temporarily mount the root file system before the real root file system is mounted. initramfs (Initial RAM file system) preloads the required block device modules like SCSI, RAID to load the actual file system. Once real file system is mounted, initrd is unmounted.

Systemd

Systemd (d at the end refers to daemon – processes that runs in background ) reads from /etc/systemd/system/default.target to determine the target. Systemd replaces the init process found in the older versions

Example of /etc/systemd/system/default.target

Description=Multi-User System
Documentation=man:systemd.special(7)
Requires=basic.target
Conflicts=rescue.service rescue.target
After=basic.target rescue.service rescue.target
AllowIsolate=yes

To find out current target of the system

[root@Master ~]# systemctl get-default
multi-user.target

To set the default target run below command

systemctl set-default type.target

multi-user.target: refers to run level 3

graphical.target: refers to run level 5

systemd targets

Runlevel	Target Units	Description
0	runlevel0.target, poweroff.target	Shut down and power off the machine
1	runlevel1.target, rescue.target	Set up a rescue shell/mode
2	runlevel2.target, multi-user.target	Non-graphical multi-user system.
3	runlevel3.target, multi-user.target	Non-graphical multi-user system.
4	runlevel4.target, multi-user.target	Non-graphical multi-user system.
5	runlevel5.target, graphical.target	Graphical multi-user system.
6	runlevel6.target, reboot.target	Reboot the system.

systemctl is used for all the service management like service start, stop, enable, disable tasks.

That’s all for the Linux Boot process, i hoped you have understood all the steps during the Linux boot process. Feel free to comment below your thoughts regarding this post.

What is /etc/passwd file and various fields in /etc/passwd

2019-11-28T15:32:00.000+05:30

If you are a Linux User or a system admin, you must have heard about /etc/passwd file. This file is a config that contains all the user details in the system and it is created during OS installation. Whenever a new user is added in the Linux system using useradd or adduser command, /etc/passwd file is updated with the details of the newly added user. This file has several fields and each field is separated by ‘:’ or colon.

There are several unix commands that uses /etc/passwd file like passwd and chpasswd – user for changing the, getent command for displaying user entries, chsh – for changing shell.

In brief, /etc/passwd is the config file that contains the login information of the users.

Contents of /etc/passwd

Below is the format of /etc/passwd file

As it is clear from the above example, /etc/passwd file contains seven entries or fields each separated by a colon. Now let us see what all are these fields.

Login Name or Username: First field in the /etc/passwd corresponds to the login name or Linux username.
x in the second field refers to the encrypted password that is stored in another file /etc/shadow. In case shadowing is disabled, then this field will contain the encrypted password.
User ID or UID: Third entry in the /etc/passwd file is for user id or uid assigned to the user. Newly added users in RHEL 7 begins from 1000
Group ID or GID: Fourth entry in the /etc/passwd file stores the Group ID or GID of Primary group
GCOS field comment: Fifth entry in /etc/passwd is the comment field that can contain any detail about user like user’s full name, department, contact number etc. GCOS stands for General Electric Comprehensive Operating System
Home Directory: Sixth entry is for home directory absolute path that is assigned to the user. In the above example, user home directory is set as /home/john that means when user john will login to the machine, he will be at /home/john
Login Shell: Last one, the seventh field in the /etc/passwd file stores the login shell assigned to a user. In the above example, user john is assigned shell /bin/bash. Common shells are /bin/bash, /bin/sh, many times you will observe this field contains /sbin/nologin or /bin/false.

Sample /etc/passwd file looks like:

sample /etc/passwd file on a rhel 7.5 machine

Permissions on /etc/passwd file

Permissions on /etc/passwd file should be read only for all user, owner of the file is root.

-rw-r--r-- 1 root root 861 Dec  5 00:50 /etc/passwd

To get any particular user details, you can use getent command

testvm:~# getent passwd john
john:x:1023:1023:Design Team:/home/john:/bin/bash
testvm:~#

You can use awk command to filter out fields of /etc/passwd file. For example, run below command to filter out all the users in the system.

cat /etc/passwd | awk -F: '{print $1}'

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