All The Useful Linux Interview Questions & Answers - 2

Q 1. How to stop a process running in Linux?
You can kill a process using:

kill PID - It is used to kill a particular process.
killall - It is also used to kill all the running processes.

Q 2. What is Linux and why it is used?
An open-source operating system, Linux is currently one of the best OSs. It can be considered as software that sits underneath and communicates with the other software on a computer and passes on requests from those software programs to the hardware.

Linux is used because it is:

Highly stable and secure
Can be maintained easily
Can run on any hardware system
Open source and free to use
Extensive documentation and support

Q 3. What is the difference between Linux and Redhat?

Redhat    Vs   Linux

1.    Specific distribution backed by the company RedHat   -    General term for the Linux OS. Can refer to any distribution.
2.    RedHat is a specific OS built on Linux Kernel.    -  Linux is essentially a kernel.
3.    To receive support and updates, one needs to have a proper agreement with the company.    -   Follows the Open source model

Q 4. What does Swap mean in Linux?
If a Linux server runs out of memory, the kernel moves some inactive processes from Linux server to a disk that acts as the virtual memory. This disk space is called a Swap.

Q 5. What are the essential features of the Linux operating system?
Multi-tasking is possible without slowing down CPU.
Offers high security compared to other OSs like Windows, iOS, etc.
Can be converted from the command line to GUI by installing required packages.
Open source code with great community and support.
Can run on different hardware types.
Hierarchical file system.
Read details about the security features of Linux in the next question of our Linux Interview questions list.

Q 6. How is Linux more secure compared to other operating systems?
There are multiple reasons for this:
Linux gives very low access to its users. If there is a virus attack, only a few files will be corrupted not the whole system.
It is less vulnerable because a user needs complete execution rights for opening even an email attachment.
The working environment in Linux is segmented in different environments like Ubuntu, Arch, Linux Mint, etc. This division gives much protection from the virus.
Linux uses Iptables which requires advanced privileges to function.

Q 7. What is the structure of Linux?

Linux has a layered structure:

Standard Utility library
Applications
The standard library of procedures
Kernel
Device drivers
Hardware

Hardware - the CPU, RAM, mouse, the keyboard is the hardware
Kernel - contains device drivers and handles resource allocation, acts as an interface between the hardware and the operating system.
The standard library of procedures - termed as libc, allows the user to communicate with the kernel.
User applications and standard utilities - the commands for various tasks like computing, modifying files or taking backups, etc.

Q 8. What are the functions of a Linux operating system?
Linux operating system is one of the popular versions of the UNIX operating system, which is designed to offer a free or low-cost operating system for personal computer users. It gained a reputation as a fast performing and very efficient system. This is a remarkably complete operating system, including a GUI (graphical user interface), TCP/IP, the Emacs editor, can X Window System, etc.

It is not limited simply to the OS but it is also used as a platform to function servers, embedded systems, and desktops.
Linux gives different distributions as well as differences because it is open-source as well as includes a modular design.

Q 9. What are the core components of Linux?
The core components of Linux are boot loader, kernel, shell, Daemons, window manager and X window server.

Q 10. What is the virtual desktop in Linux?
Virtual desktop provides secure access to Linux VDI even from non-Linux devices like Windows. This helps admins manage Windows and Linux applications using one console.

Q 11. How do I get to a command prompt in Linux?
You can use the key combination Ctrl+Alt+T to open a command prompt in Linux.

Q 12. How do I run a file in Linux?
Open the command prompt using Ctrl+Alt+T
If your file does not have to execute permission, add the same chmod +x /root/home/your file.sh
Run the script by typing /root/home/your file.sh and press enter.

Q 13. How do I check hard drive space on Linux?
Use df [options] [devices] to check hard drive space.

Example:

df -h /test/tmp gives output as

Filesystem

Inodes 

IUsed

IFree

IUse%

Mounted On

/test/tmp

453K

23

433

1%

/

Q 14. What is Lilo how is it useful in Linux?
LILO stands for Linux Loader that is used to load Linux into memory. It can boot operating systems from floppy disks, hard disks, and it does not depend on a specific file system. Lilo handles some tasks such as locate the kernel, identify other supporting programs, load memory and starts the kernel.

Q 15. What is export Ld_library_path?
It is an environment variable that contains a list of paths that are used to resolve the library dependencies at run-time (dynamic libraries). This path is checked before the standard paths /lib or /usr/lib.

Q 16. What do you mean by ldconfig in Linux?
Idconfig is a command that creates the required links and cache to the most recently shared libraries that are present in the directories specified in the

command line,
the file /etc/ld.so.conf,
the trusted directories /lib and /usr/lib

Q 17. What is GUI in Linux?
Graphical User Interface or GUI makes it easier for a Linux user to execute programs via a desktop, similar to Windows. The desktops in Linux are KDE, Java, GNOME.

Q 18. What is puppet used for in Linux?
Puppet is a Configuration Management tool. It is used to
Deploy, configure and manage servers,
Define and monitor unique configurations for each host
Scale-up and scale-down machines dynamically
Provide control over configured devices to propagate changes in a centralized manner

Q 19. How to enhance the security of password file in Linux?
For enhanced security, a shadow copy of the password file is made, which stores hashed passwords of all the users. The hashed password is a long string of characters, generated based on the hashing method used.

Q 20. What is the use of a symbolic link in Linux?
A Symbolic link: 
links the libraries
ensures that the files are in their place without the original being copied or moved.

Q 21. Compare cron and anacron in Linux with an example?

Cron Vs    Anacron

1.    It is a daemon that runs scheduled tasks -    It runs commands periodically, the frequency being defined in several days.
2.    Example: updates, system backups    - Example: a backup script that is scheduled to run weekly or monthly.
3.    Suitable for machines that are on 24x7 like servers     - Suitable for machines like laptops and desktops that are NOT on 24x7.
4.    Runs as per defined schedules. -    Checks if any job has to be executed when the user turns on the power.
5.    Default system crontab file is /etc/crontab - Listed in /etc/anacrontab

Q 22. What is a daemon process in Linux?
A program that gets executed in the background because of the occurrence of a specific event, process or condition. Daemon processes are managed by the Kernel. The operations are given unique PIDs.

Q 23. What is the difference between filesystems ext2, ext3 and ext4 in Linux?

1.    ext2    Second extended filesystem.
2.    ext3    The concept of journaling was introduced, wherein, if a system crash or power failure occurred, the filesystems that were not saved could be recovered, unlike ext2.
3.    ext4    Performance improvements over the ext3 filesystem. Supports huge filesizes.

Q 24. List 10 networking and troubleshooting commands in Linux.

Ifconfig - configure interface parameters of the network.
dig - performs DNS lookups to display a result obtained from name servers.
traceroute - prints the route that the packets take to the network host.
nslookup - queries internet domain name servers.
telnet - connect destination port if the connection between hosts is working fine
netstat - reviews each network connection and the open sockets.
w - writes (prints) current activities and processes by each user.
scp - secure copy the files from and to another host in the network.
ifup/ifdown - enable or disable the network interface respectively.
nmap - checks for the opened port on the server

Q 25. How to give permission to full permission in Linux?
Use chmod 777 to give full permission to reading, write and execute.

Q 26. list the different modes of using vi editor in Linux?
There are three modes - command mode, insert mode and last line or escape mode.

Q 27. How to Uninstall Software with the Command Line in Linux?
Use the command apt-get as - 

       apt-get --purge remove [filename]

Q 28. What are system calls in Linux?
There are 80 system calls in Unix that are used to control processes, manage filesystem and for inter-process communication. System calls occur in the kernel.

Q 29. Which command in Linux is used for the description of any command?
For this access the individual command's manual page. For instance, to know the description of

    cat command, type

man cat

This will display a description of the said command.

Q 30. How many types of bond are there in Linux?
There are 7 types of network bond in Linux - mode=0 (balance-rr), mode-1 (active-backup),

      mode=2 (balance-xor), mode=3 (broadcast), mode=4 (802.3ad), mode=5 (balance-tlb),

      mode=6 (balance-alb)

Q 31. List important Linux Operating System commands
Some highly important Linux commands are listed below:

adduser    -     Add a new user
info    -     Help info
id    -     Print user and group id’s
arch    -     Print machine architecture
chown    -     Change the user and group ownership of files
hostname    -     Print or set system name
head    -     Output the first part of the file(s)
awk    -     Find and Replace text within file(s)
chroot    -     Change the root directory
cksum    -     Print CRC checksum and byte counts
clear    -     Clear terminal screen
chmod    -     Change the access permissions of files and directories
bc    -     An arbitrary precision calculator language
chkconfig    -     tool for maintaining the /etc/rc[0-6].d directory hierarchy
cal    -     Display a calendar
du    -     Estimate file space usage
chgrp    -     Change the group ownership of files
dirname    -     Convert a full pathname to just a path
dircolors    -     Colour setup for `ls’
cat    -     Concatenate files and print on the standard output
dir    -     Briefly list directory contents
chdir    -     Change working directory
diff3    -     Show differences among three files
cmp    -     Compare two files
diff    -     Display the differences between two files
comm.    -     Compare two sorted files line by line  copy a file
df    -     Display free disk space
cp    -     Copy one or more files to another location
dd    -     Data Dump    -     Convert and
dc    -     Desk Calculator
gawk    -     Find and Replace text within file(s)
gzip    -     Compress
cron    -     Daemon to execute scheduled commands
date    -     Display or change the date & time
crontab    -     Schedule a command to run at a later time
cut    -     Divide a file into several parts
csplit    -     Split a file into context-determined pieces
env    -     Display, set, or remove environment variables
fdformat    -     Low-level format a floppy disk
grep    -     Search file(s) for lines that match a given pattern
echo    -     Display message on screen
format    -     Format disks or tapes
fold    -     Wrap text to fit a specified width
fmt    -     Reformat paragraph text
ed    -     A line-oriented text editor (edlin)
find    -     Search for files that meet the desired criteria
fgrep    -     Search file(s) for lines that match a fixed string
egrep    -     Search file(s) for lines that match an extended-expression
eject    -     Eject CD-ROM
fdisk    -     Partition table manipulator for Linux
expand    -     Convert tabs to spaces
false    -     Do nothing, unsuccessfully
free    -     Display memory usage
factor    -     Print prime factors
fsck    -     Filesystem consistency check and repair or decompress named file(s)
expr    -     Evaluate expressions
grep    -     Search file(s) for lines that match a given pattern
groups    -     Print group names a user is in