What is Grub

Grub stands for Grand Unified Boot Loader, which is responsible to load the kernel into the memory and boot your Linux operating system. Grub can load other operating systems like window xp/2000/2003/2008, Mac OS, Free BSD,Net BSD as well.

Grub is the replacement of older Linux bootloader ‘LILO’.

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Linux Boot Process

Some curious folk asked me how Linux system boots, what is process behind it. I thought to share with all, so here I will tell you how Linux boot process works.

We Linux users spend a lot of time on our computers,but we never think,how our Linux system boots? What is the process behind the startup of our Linux operating system. To better understand the boot process we should have good knowledge about the Grub, MBR, BIOS,Boot Loader and initrd etc….which we will discuss here later.

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Introduction to OpenSSH

SSH stands for Secure Shell. It is a network protocol which is used to access a remote system. SSH offers utilities like scp & Slogin to remotely login & copy data on a remote system, which are a secure versions of rcp & rlogin. It is the only network service which is enabled by default. SSH is replacement of Telnet, which does not support encryption, where everything goes in plain text. Thats is why for the security reason, SSH has become the most trustworthy and used protocol. SSH is available for most of the operating systems, including Microsoft Windows.

SSH supports encryption which make it a very secured and trustworthy protocol. Unencrypted Communication on a network can be dangerous, because a hacker can trace your user name & password and can easily steal your important data. SSH uses two keys to do encryption:

1] Private key: This key is always stores on the ssh server
2] Public key: This key is distribute between ssh clients.

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15 Tech Mahindra Interview Questions for Linux Administrator

Question1. How would you check line number 21 to 30 in a file with 100 lines with just one command ?

Question2. how to check last 2 lines of a file ?

Question3. How would you find .txt files in current directory, created/updated in last 30 minutes ?

Question4. What would be the syntax to run cron every 15 minutes ?

Question5. What is syntax to run cron at 10hour 14 minute on every sunday?

Question6. What are the different fields in cronjob stands for ?

Question7. How to check if last command ran successful

Question8. User vinod is running some process. How would you get that particular process running by vinod with just single command ?

Question9. Difference between public and private ip ?

Question10. How to check which user is currently logged on ?

Question11. Which command would get me 3rd column from a file ?

Question12. Which command would get me 3rd character from first line in file ?

Question14. What is /dev/null file ?

Question15. What is difference between standard input, standard output, and standard error ?