Linux Interview Questions

 Categories of Linux Interview Questions

• Linux Technical Interview Questions 
• Linux Interview Questions For Experienced

Q25. What is the importance of the GNU project?

Ans. GNU being a free software movement provides several advantages as it gives the flexibility to modify the programs according to their use and convenience. It is also allowed to redistribute the modified copies of the software for free and release it for the public to use it.

Q26. How can a command prompt be opened while writing a command?

Ans. The command prompt is found in the default shell and to open it Ctrl-Alt-F1 is pressed. This will start the command-line interface (CLI) from which commands can be entered and executed.

Q27. What is the preferred size of a swap partition in Linux?

Ans. Generally, the size of the swap partition is twice the size of the physical memory present in the system. If it is not possible to have this size, then the minimum required size for a swap partition is the amount of memory present in the system

Q28. Define Virtual Desktop?

Ans. This is a special feature which is very useful for the users who enhance the physical boundaries of a screen to a larger extent. With a virtual desktop, a virtual screen is created that can expand the normal screen of the system. A virtual desktop can be implemented by using 2 ways

Switching Desktops

With switching desktops, distinct virtual desktops can be created to run programs. Each virtual desktop acts as a separate desktop and programs executing on these desktops can only be accessed by the users who are using that particular virtual desktop 

Oversized Desktops

It does not provide distant desktops but lets the user scroll over a desktop that is expanded and is larger in size than the desktop having a normal physical screen. 

Q29. What are symbolic links in Linux?

Ans. Symbolic links are the same as shortcuts in Windows and they point to files or directories and programs. It provides instant access to the desired directories or files without going to the full pathname.

Linux Technical Interview Questions

Q30. Explain daemons in Linux?

Ans. Daemons are those computer programs that run as a background process to execute those functions that are not there in the base Operating System. They are used to run the services in the background so that they can not be directly controlled by the end-users. They are also used to handle periodic requests so that these requests can be sent to the appropriate programs for implementation. 

Q31. What are the commands to change permissions in Linux?

Ans. Only system administrators or file owners can grant or change the access permissions in Linux. Permissions are granted using the chmod command. + symbol is used to add permission and – symbol is used to deny permission, followed by any of these letters: u (user), o (others), g (group), an (all), r (read), w (write) and x (execute). For instance, the command chmod u+rw FILE23.TXT is used to grant read and write access to the file FILE23.TXT, which is assigned to users.

Q32. Write down the process states in Linux?

Ans. The process states in Linux are:

• Ready: The process is ready for execution
• Running: The process is in the execution state
• Blocked or wait: Process is waiting for input or is blocked for execution from the user
• Terminated or Completed: Process is successfully completed or was terminated due to some error by the Operating System
• Zombie: The process is terminated by the system, but the information is still there in the process table.

Q33. What are the ways to access partitions under Linux?

Ans. In Linux, numbers are assigned as a suffix to the drive identifier. For instance, the first IDE hard drive had three primary partitions, will be written as name/number just like /dev/hda1, /dev/hda2, and /dev/hda3.

Q34. What is the use of the grep command in Linux?

Ans. Grep is the term used for Global Regular Expression Print. It is used to search for a text expression in a file by matching the patterns based on a regular expression.

It follows the following syntax

Syntax: grep [text options] pattern [filename]

For Example:

$ grep -c "shell script" inlinux.txt

This command will print the count of the word “shell script” in the “inlinux.txt” file.

Q35. What do hard links refer to in Linux?

Ans. Hard links are the links that point directly to the file and not to the pathname. It means even if the file is renamed or moved from one location to the other, the link will remain the same as the link is for the file and not for the path where the file is located.

Q36. What is Process Management System Calls in Linux?

Ans. Process management system calls are:

• fork () – It is used for the creation of a new process
• exec(): It is used for the execution of a new program
• wait(): It is used to direct the system to wait until the process execution is finished
• exit(): It is used to exit from the current process
• System Calls that are used to get Process ID are:
• getpid():- It is used to get the unique process id (pid) of the process
• getppid():- It is used to get the unique id of the parent process

Q37. What is the role of the ‘ls’ command in Linux?

Ans. The ls command lists down all the files in a particular directory. The syntax for using this command is:

$ ls  

For instance: The command to list all the files in the tutorial directory will be as follows:

$ ls tutorial/

Different options can be used with the ls command to provide extra information about the file/folder from where information needs to be fetched. The options are:

• l  Lists long format(displays the access permissions of the file)
• a  lists all the files including hidden files
• i  lists all the files along with their inode number
• s  lists all the files along with their size
• S  Lists all files with their respective size and sorts the list by the size of a file
• t   sorts all the listed files by their date and time

Q38. What are filenames that are preceded by a dot?

Ans. Generally, all the hidden files are preceded by a dot. These files hold important or setup info as they can be configuration files. Keeping these files as hidden makes them secure from being accidentally deleted.

Q39. What is the use of a redirection operator in Linux?

Ans. The redirection operator is used when there is a need to use the output of one command as an input to the other command or file. It is generally used in 2 ways

‘>’ – this operator overwrites the existing data in the file or makes a new file.

‘>>’ appends the new data at the end of the file or makes a new file. 

So in simple words, in this ‘>’ redirection operator, the data in the file is overwritten and in this ‘>>’ redirection operator, the data is appended.

Q40. Is it possible to execute more than 1 command from a single command line entry? If yes, how?

Ans. Yes, it is possible to execute several commands from a single command line entry by separating them using a semicolon symbol. For instance: Consider the example below in which a series of commands are issued from a single entry.

ls –l cd .. ls –an EXAMPLE of having 3 commands from the single line: ls -l cd.. ls -an EXAMPLE

Q41. What is the use of the tar command in Linux?

Ans. An archived file can be created or extracted by using the tar command in Linux. For instance: to extract all the files from the archive ‘example.tar.gz’, the following command will be used:

$ tar -xvzf example.tar.gz

To create an archive of all the file stored in /home/linux/, the following command can be used:

$ tar -xvzf filename.tar.gz

where c refers to create an archive, x refers to extract, v refers to verbose and f refers to file

Q42. How programs can be shared across different virtual desktops in Linux?

Ans. For sharing the programs across different virtual desktops, press the button in the upper left-hand corner of a window which appears to be a pushpin. It will "pin" that application thus making it visible at the same position on the physical screen in all virtual desktops.

Q43. What does Latch mean in Linux?

Ans. A Latch is a binary storage device that stores the file temporarily and is controlled by a timing signal with the value being either 0 or 1. It has two stable states. The high output state denotes 1 and a low output state denotes 0. If the power is on, it can store 1 bit of data. 

Q44. What does a nameless or empty directory signify in Linux?

Ans. In Linux, an empty directory acts as the nameless base of the file system. It serves as an attachment for all other files, directories, devices, and drives.

Q45. What is a Microprocessor?

Ans. It is a single-chip device that is used to execute commands. It fetches, decodes, and then decodes the instructions from the memory. The basic functions carried out by microprocessor are:

basic mathematical operations such as add, subtract, multiply, and divide

moving data from one place to another

decision making based on the conditions and then moving on to new instructions based on those decisions. 

Q46. What does the pwd command do?

Ans. The pwd command refers to the print working directory. It displays the pathname of the directory which is currently in use.

For instance: If we will write the below command

Pwd

The following output will be generated:

/home/ajay12/myDir 

Q47. Explain Regular Expressions in Linux

Ans. Regular Expressions in Linux are used to search for options with specified patterns. Some commands used with regular expressions are sed, tr,vi and grep.

Some symbols used with Regular Expressions are:

.	To match any character
$	To match the end of the String
^	To match the beginning of the String
	It is used to depict special characters
*	To match zero or more than one characters
?	It is used to match exactly one character

Q48. How switching from one desktop environment to another can be done such as KDE to Gnome?

Ans. Considering that these two desktop environments are already installed, just log out from the current session through the user interface. Then again login from the login screen by entering the ID and password and choose the session type you wish to continue with. This will remain the default desktop environment until you change it to some other environment.

Linux Interview Questions For Experienced

Q49. What is the effect of case sensitivity while using the commands?

Ans. Linux being a case sensitive language, it can alter the output if every character is not encoded as it is including the uppercase and lowercase letters. For instance- CD, cd, and Cd will produce different outputs as these are three different commands. If a command is written in lowercase where it should be in uppercase, it will generate different results.

Q50. How many disk partitions are required to install Linux?

Ans. Minimum 2 partitions are required to install Linux. In one partition, all the local files are stored including configuration files of the OS, application files and services along with user files. The second partition is used as Swap Space which is an extended memory for RAM in Linux. 

Q51. Define environmental variables?

Ans. Environmental variables are also known as global shell variables. They are global settings responsible for controlling the shell’s function along with other Linux programs.

Q52. How shortcuts can be created for long path names?

Ans. Shortcuts can be created by using a feature called filename expansion in which the TAB key is used for this purpose. The condition is that the pathname should be unique and the shell which is in use should support this feature. For instance, pathname /home/shell/example directory, will be written as follows: /ho[tab]/she[tab]/exa[tab].

Q53. List down the modes that are used while using vi editor?

Ans. Vi editor uses 3 modes for its functioning

• Command mode – This is the mode from where the commands are initiated
• Edit mode – This is the mode from where text editing is done
• Ex mode – This is the mode where instructions are given to interact with Vi to process a file.

Q54. What does the Ctrl+Alt+Del key combination do in Linux?

Ans. It works similarly as in windows to restart a system. The only difference is that the reboot starts immediately in Linux after striking this key combination without giving any notification or confirmation message.

Q55. What does /usr/local directory stores?

Ans. This directory holds locally installed files and is mainly used in the environments where files are generally stored in a network. They are used for those software packages that are installed from the source or software that are not official to use. Local files normally go to /usr/local/bin, /usr/local/lib etc. kinds of directories in Linux.

Q56. List down some of the Linux distributors with its usage?

Ans.  Linux distributors are often called Distros. Different parts of LINUX such as the kernel, graphical programs, system environment etc. are developed and distributed by different organizations. Distros assemble these parts and compile them in an operating system that is ready to be installed in a system for use. There are more than six hundred Linux distributors in the market but some of the well-known distributors are

• UBuntu: It is the most common Linux Distribution that comes with many pre-installed apps and repositories in its library. It is extremely user-friendly, easy to use, and works similarly to a MAC operating system.
• Debian: It is the fast, stable, and user-friendly Linux Distribution.
• Linux Mint: It is mostly used by those who are not used to Linux as it works on windows.
• Fedora: It provides the latest version of Linux but is less stable as compared to other distributions. By default, it has the GNOME3 desktop environment.
• Arch Linux: This is not suggested for beginners as every package needs to be installed by the users according to their requirements.
• Red Hat Enterprise: It is a stable and durable distribution from Linux that is mostly used for commercial purposes and therefore needs to be tested rigorously before releasing it.

Q57. How comments can be inserted in the command line prompt?

Ans. Comments are always followed by a # symbol in Linux. From this symbol, shell understands that this is a comment and not a command. Shell completely ignores the content which is followed by # symbol. For instance "# Comment is followed by this symbol and not the command."

Q58. How memory usage can be tracked in LINUX?

Ans. It is important to determine the total memory used by different programs in Linux in order to analyze whether the resources and the server is being used adequately by the users or not. Below are some of the methods to find out the memory in use. 

Free command: Memory usage can be checked by this simple command. For instance, ‘$ free –m’, in this command’ displays all the data in MBs.

Vmstat: With this command, the memory usage statistics can be known. For instance, ‘$ vmstat –s’

/proc/meminfo: Memory in use can also be known by reading the file /proc/meminfo file. For instance,  ‘$ cat /proc/meminfo’

Top command: Total memory which is in use along with the RAM usage can be determined by using this command.

Htop: Memory usage along with other useful details can be displayed by using this command.

Q59. How can an ongoing process be terminated?

Ans. Every process has a unique id known as pid in Linux. Kill command followed by pid is used to terminate a process. To terminate all the processes in one go, kill 0 is followed by pid.

Q60. How does command grouping work in Linux?

Ans. Parentheses can be used to group commands in Linux. For instance, To send the recent date and time along with a file named EXAMPLE to a second file named GROUPING, command grouping can be applied by using this command (date cat EXAMPLE) >GROUPING