Linux 200+ Interview Questions for Freshers - Solved:


We have prepared a set of questions to help Freshers and Experienced Linux Admins in their preparations for Interview. This list includes Google interview questions for Linux Admin, Amazon interview questions for Linux admin and other reputed firms as well.
You will find these questions very helpful in your Linux Admins interviews. Prepare well and All the very best.

All the feedbacks and suggestions are most welocome.

  1. When you login you get “$” prompt, what is the prompt for root?
  2. Explain the difference between grep and egrep?
  3. What is the port for DNS, NTP and NFS? 53,123 and 111/2049
  4. What is the configuration file name of DNS and where is it located? /etc/named.conf
  5. How many new directories will be created after running the following command mkdir {a..c}{1..3} 9
  6. Your PC is configured with a DNS server address but not the default gateway. Can the PC access internet? No
  7. What is the difference between IP and Gateway? Search online
  8. Can you assign one static IP to 2 computers, if not then why? No because it will create IP conflict
  9. How to change IPs address to static? ifconfig x.x.x.x
  10. You are trying to ping a server by hostname and you get an error message, “ping: unknown host …”. What could be the reason and how to solve the problem so you can ping it by hostname? Check for /etc/hosts or DNS to see if it has hostname to IP entry
  11. Explain the difference between relative and absolute path? Absolute path starts from / where relative path is your current directory
  12. List 3 different methods of adding user? Search online
  13. What is the command to change file/directory ownership and group? chown and chgrp
  14. List any 3 type of filesystem? ext4,NTFS and FAT
  15. When you login you get a message on the screen. What is the name of that file and where is it located? /etc/motd
  16. What is /bin directory used for? Search online
  17. What are the different types of DNS Server Master and secondary
  18. How to change a user password? passwd username
  19. What is the version of Redhat Linux you have experience with? 7.4
  20. List any 4 linux distributions? Redhat, CentOS, Ubuntu and SUSE
  21. How to logoff from the system? exit
  22. Give any 3 examples of operating systems? Windows, Linux and MAC
  23. How to create a directory? mkdir
  24. Where are the zone files located for DNS service? /var/named/zonefiles
  25. How to check kernel version? uname –a
  26. Which directory has all the configuration files? /etc
  27. How to become root user from a regular user? su –
  28. How many mega bytes in 1 giga bytes? Search online
  29. What is the purpose of having different network ports? So the communication of each application goes through a dedicated port
  30. How to display first column of a file? cat filename | awk ‘{print $1}’
  31. What is the name of DNS rpm package? bind
  32. What is the difference between nslookup and dig commands? Search online
  33. How to check your user id and group id? id
  34. How to check a file’s permission? ls –l
  35. What is the difference between “kill” and “kill -9” command? Search online
  36. What is subnet? Search online
  37. You are troubleshooting an issue with Redhat support and they have asked you to send the contents of /etc directory. How and which method you will use to transfer the contents? tar (compress) the entire /etc directory and ftp
  38. What is root home directory? /root
  39. What is rsyslogd deamon and its purpose? Search online
  40. Your company has terminated a server administrator. What is first thing as an administrator you should do to enhance the security? Change root password
  41. How to check the computer name or host name in Linux? hostname
  42. Which permission allows a user to run an executable with the permissions of the owner of that file? First 3 bits should have x
  43. What is the command to untar a tarred file? untar
  44. What is /proc directory used for? Search online
  45. What is the purpose of nsswitch.conf file It tells the system where to go to resolve hostnames
  46. List 3 basic commands to navigate the filesystem? cd, pwd and ls
  47. Which service/daemon should be running on the server that allows you to connect remotely? sshd
  48. What is the purpose of firewall? Search online
  49. List any 3 IT components? Hardware, OS and Applications

  1. Which directory has all the commands we use, e.g. ls, cd etc.? /usr/bin or /bin
  2. What is the difference between memory, virtual memory and cache? Search online
  3. Which of the following is correct? a. Hardware   Operating System   Users b. Operating System   Users   Hardware c. Database   Hardware   Users
  4. Which of the following is a communication command? o grep o mail o touch o cd
  5. How to rename a file or directory? mv
  6. How to change a hostname in Linux? Search online
  7. How to check network interfaces in Linux? ifconfig
  8. Why is “tail –f logfilename” command used most often and what does it do? It will output all incoming logs in real time
  9. What type of hardware have you worked on? You should get yourself familiar with Dell, HP and UCS hardware by going online and check the vendor websites
  10. How to sort a file in reverse order? cat filename | sort –r
  11. What is the name of operating system that runs Unix? Solaris, HP-UX etc.
  12. List all byte sizes from smallest to largest? Search online
  13. How to check the total number of partition in Linux? fdisk -l
  14. How to access a linux system from a linux system? ssh
  15. Explain the procedure of bonding 2 NICs or interfaces together? Search online
  16. What is the exact command syntax to list the 5th column of a file and cut the first 3 letters? cat filename | awk ‘{print $5}’ | cut –c1-3
  17. What is /etc/hosts file used for? To resolve hostnames with IP address
  18. List any 3 options of ‘df’ command and what they are used for? Search online
  19. What is the command to change file/directory permissions? chmod
  20. What is the purpose of pipe (|)? To combine multiple commands
  21. What is /etc directory used for? For configuration files
  22. Which command is used to list files in a directory? ls –l
  23. There is a command which gives you information about other commands, please explain that command and what is it used for? man
  24. How to delete a file and a directory? rm filename and rmdir dirname
  25. What is the difference between “tail” and “tail -10”? None
  26. List 4 commands to display or read a file contents? cat, more, less, vi

  1. Which command is used to read the top 5 lines of a file? head -5 filename
  2. What are the different commands or methods to write to a file? echo > filename and vi filename
  3. What is swap space and how to check swap space? Search online
  4. What is inode and how to find an inode of a file? Search online
  5. Which file to edit for kernel tuning? Search online
  6. What is the latest version of Redhat? Search online
  7. Name the command to find specific word from a file? grep word filename
  8. You have scheduled a job using crontab but it does not run at the time you specified, what could be the reason and how would you troubleshoot? Check your system time Check your crontab entry Check /var/log/messages
  9. How to check system hardware information? dmidecode
  10. How to check network interface MAC address? ifconfig
  11. If I don’t want others to read my file1, how to do that? Remove r from the last 3 bits of file permission
  12. What is the purpose of “uniq” and “sed” command? Search online
  13. Which command is used to list the contents of a directory in the most recent time and in reverse order, meaning the most updated file should be listed on the bottom? ls –ltr
  14. What is the difference between tar, gzip and gunzip? Search online
  15. What are the different ways to install and OS? DVD, DVD iso and network boot
  16. How to view difference between two files? diff file1 and file2
  17. You noticed that one of the Linux servers has no disk space left, how would you troubleshoot that issue? If running LVM then add more disk and extend LVM If not running LVM then add more disk, create a new partition and link the new partition to an existing filesystem
  18. How to check Redhat version release? uname –a or /etc/redhat-release
  19. What is the difference between TCP and UDP? Search online
  20. What is a zombie process? Search online
  21. How do you search for a pattern/word in a file and then replace it in an entire file? sed command
  22. Explain the purpose of “touch” command? To create an empty file
  23. If a command hangs, how to stop it and get the prompt back? Ctrl C
  24. Which command is used to count words or lines? wc
  25. How to check the number of users logged in? who
  26. What is the command to view the calendar of 2011? cal 2011
  27. Which command is used to view disk space? df –h
  28. How to create a new group in Linux? groupadd
  29. What is the command to send a message to everyone who is logged into the system? wall
  30. Which command is used to check total number of disks? fdisk –l
  31. What is an mail server record in DNS? MX
  32. What does the following command line do? ps -ef | awk '{print $1}' | sort | uniq List the first column of all running processes, sort them and remove duplicates
  33. You get a call that when a user goes to www.yourwebsite.com it fails and gets an error, how do you troubleshoot? Check for user internet Check to see if user computer has DNS for hostname lookup Check to see if the server is up that is running that website Check to see if the server’s web service is running Check for DNS availability which is resolving that website
  34. List 4 different directories in /? /etc, /bin, /tmp, /home
  35. What is the output of the following command: $tail -10 filename | head -1 It will show the first line from the last 10 lines of a file
  36. What are the different fields in /etc/passwd file? Search online
  37. Which command is used to list the processes? ps –ef
  38. What is the difference between “hostname” and “uname” commands? Hostname will give you system name and uname will give you OS information
  39. How to check system load? top and uptime command
  40. How to schedule jobs? crontab and at
  41. What is the 3rd field when setting up crontab? Day of the month
  42. What is the command to create a new user? useradd
  43. What is the “init #” for system reboot? 6
  44. How to restart a service? systemctl restart servicename
  45. How to shutdown a system? shutdown or init 0
  46. What is “ftp” command used for? To transfer files from one computer to another
  47. Explain cron job syntax? First is minute, second is..? Min, house, day of the month, month, day of the week and command
  48. How to delete a package in Linux? rpm –e packagename
  49. What is the file name where user password information is saved? /etc/shadow
  50. Which command you would use to find the location of chmod command? which chmod

  1. Which command is used to check if the other computer is online? ping othercomputer
  2. Please explain about LAN, MAN and WAN? Search online
  3. How to list hidden files in a directory? ls –la
  4. What is the difference between telnet and ssh? ssh is secure where telnet is not
  5. How to run a calculator on Linux and exit out of it? bc and quit
  6. List any 4 commands to monitor system? top, df –h, iostat, dmesg
  7. You are notified that your server is down, list the steps you will take to troubleshoot? Check the system physically Login through system console Ping the system Reboot or boot if possible
  8. What is difference between static and DHCP IP? Search online
  9. How to write in vi editor mode? i = insert, a = insert in next space, o = insert in new line
  10. What is the difference between “crontab” and “at” jobs? crontab is for repetitive jobs where at is for one time job
  11. What is vCenter server in VMWare? Search online
  12. What is “dmidecode” command used for? To get system information
  13. What is the difference between SAN and NAS? Search online
  14. What is the location of system logs? E.g. messages /var/log directory
  15. How to setup an alias and what is it used for? alias aliasname=”command” It is used to created short-cuts for long commands
  16. What is the purpose of “netstat” command? Search online
  17. What are terminal control keys, list any 3? Crtl C, D and Z
  18. Which command(s) you would run if you need to find out how many processes are running on your system? ps –ef | wc –l
  19. What are the different types of shells? sh, bash, ksh, csh etc.
  20. How to delete a line when in vi editor mode? dd
  21. Which is the core of the operating system? a) Shell b) Kernel c) Commands d) Script
  22. Which among the following interacts directly with system hardware? a) Shell b) Commands c) Kernel d) Applications
  23. How to save and quit from vi editor? Shift ZZ or :wq!
  24. What is the difference between a process and daemon? Search online
  25. What is the process or daemon name for NTP? ntpd

  1. What are a few commands you would run if your system is running slow? top, iostat, df –h, netstat etc.
  2. How to install a package in Redhat Linux? yum install packagename
  3. What is the difference between “ifconfig” and “ipconfig” commands? ifconfig for Linux and ipconfig for Windows
  4. What is the first line written in a shell script? Define shell e.g. #!/bin/bash
  5. Where is the network (Ethernet) file located, please provide exact directory location and file name? /etc/sysconfig/network-scripts/ifcfg-nic
  6. Why do we use “last” command? To see who has logged in the system whether active or logged off
  7. What is RHEL Linux stands for? Search online
  8. To view your command history, which command is used and how to run a specific command? history and history #
  9. What is NTP and briefly explain how does it work and where is the config files and related commands of NTP? Search online
  10. How to disable firewall in Linux? Search online
  11. How to configure mail server relay for sendmail service? Edit /etc/mail/sendmail.mc file and add SMART_HOST entry
  12. Where is samba log file located? /var/log/samba
  13. What is mkfs command used for? To create a new filesystem
  14. If you create a new group, which file does it get created in? /etc/group
  15. Which file has DNS server information (e.g. DNS resolution)? /etc/resolv.conf
  16. What are the commands you would run if you need to find out the version and build date of a package (e.g. http)? rpm –qi http
  17. On the file permissions? What are the first 3 bits for and who is it for? Read, write and execute. They are used for the owner of the file
  18. How to create a soft link? ln –s
  19. How to write a script to delete messages in a log file older than 30 days automatically? Search online
  20. How to quit out of “man” command? q
  21. Which command is used to partition disk in Linux? fdisk
  22. What is the difference between “shutdown” and “halt” command? Search online
  23. What is the exact syntax of mounting NFS share on a client and also how to un-mount? Search online
  24. What experience do you have with scripting, explain? if-the, do-while, case, for loop scripts
  25. How to get information on all the packages installed on the system? rpm –qa
  26. Explain VMWare? Search online
  27. You are tasked to examine a log file in order to find out why a particular application keep crashing. Log file is very lengthy, which command can you use to simplify the log search using a search string? grep for error, warning, failure etc. in /var/log/messages file
  28. What is /etc/fstab file and explain each column of this file? Search online
  29. What the latest version of Windows server? Search online
  30. What is the exact command to list only the first 2 lines of history output? history | head -2
  31. How to upgrade Linux from 7.3 to 7.4? yum install update
  32. How to tell which shell you are in or running? $0
  33. You have tried to “cd” into a directory but you have been denied. You are not the owner of that directory, what permissions do you need and where?
              • r – x
  35. What is CNAME record in DNS? Entry for hostname to hostname
  36. What is the name of VMWare operating system? ESXi
  37. What is the client name used to connect to ESXi or vCenter server? vSphere client
  38. You get a call from a user saying that I cannot write to a file because it says, permission denied. The file is owned by that user, how do you troubleshoot? Give write permission on the first 3 bits
  39. What is the latest version of VMWare? Search online
  40. What is the name of firewall daemon in Linux? firewalld
  41. Which command syntax you can use to list only the 20th line of a file? Search online
  42. What is the difference between run level 3 and 5? 3 = Boot system with networking, 5 = boot system with networking and GUI
  43. List a few commands that are used in troubleshooting network related issue? netstat, tcpdump etc.
  44. What is the difference between domain and nameserver? Search online
  45. You open up a file and it has 3000 lines and it scrolled up really fast, which command you will use to view it one page at a time? more or less
  46. How to start a new shell. E.g. start a new ksh shell? Simply type ksh, or bash
  47. How to kill a process? kill processID
  48. How to check scheduled jobs? crontab –l
  49. How to check system memory and CPU usage? free and top
  50. Which utility could you use to repair the corrupted file system? fsck
  51. What is the command to make a service start at boot? systemctl enable servicename
  52. How to combine 2 files into 1? E.g. you 3 lines in file “A” and 5 lines in file “B”, which command syntax to use that will combine into one file of 3+5 = 8 lines cat fileA >> fileB
  53. What is echo command used for? To output to a screen
  54. What does the following command do? echo This year the summer will be great > file1 It will create a new file “file1” with the content as “This year the summer will be great”
  55. Which file to modify to allow users to run root commands /etc/sudoers
  56. You need to modify httpd.conf file but you cannot find it, Which command line tool you can use to find file? find / -name “httpd.conf”
  57. Your system crashed and being restarted, but a message appears, indicating that the operating system cannot be found. What is the most likely cause of the problem? The /boot file is most likely corrupted

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