Top 200 Latest Linux Interview Questions Answers

We have creating following list for Linux  Interview questions and best possible answers.

Q1. When you login you get “$” prompt, what is the prompt for root?
Answer: #
2. Explain the difference between grep and egrep?
3. What is the port # for DNS, NTP and NFS?
Answer: 53,123 and 111/2049
4. What is the configuration file name of DNS and where is it located?
Answer: /etc/named.conf
5. How many new directories will be created after running the following command
 mkdir {a..c}{1..3}
Answer: 9
6. Your PC is configured with a DNS server address but not the default gateway. Can the PC access internet?
Answer: No
7. What is the difference between IP and Gateway?
8. Can you assign one static IP to 2 computers, if not then why?
Answer: No because it will create IP conflict
9. How to change IPs address to static?
Answer: 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?
Answer: Check for /etc/hosts or DNS to see if it has hostname to IP entry
11. Explain the difference between relative and absolute path?
Answer: Absolute path starts from / where relative path is your current directory
12. List 3 different methods of adding user?
13. What is the command to change file/directory ownership and group?
Answer: chown and chgrp
14. List any 3 type of filesystem?
Answer: 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?
Answer: /etc/motd
16. What is /bin directory used for?
17. What are the different types of DNS Server
Answer: Master and secondary
18. How to change a user password?
Answer: passwd username
19. What is the version of Redhat Linux you have experience with?
Answer: 7.4
20. List any 4 linux distributions?
Answer: Redhat, CentOS, Ubuntu and SUSE
21. How to logoff from the system?
Answer: exit
22. Give any 3 examples of operating systems?
Answer: Windows, Linux and MAC
23. How to create a directory?
Answer: mkdir
24. Where are the zone files located for DNS service?
Answer: /var/named/zonefiles
25. How to check kernel version?
Answer: uname –a
26. Which directory has all the configuration files?
Answer: /etc
27. How to become root user from a regular user?
Answer: su –
28. How many mega bytes in 1 giga bytes?
29. What is the purpose of having different network ports?
Answer: So the communication of each application goes through a dedicated port
30. How to display first column of a file?
Answer: cat filename | awk ‘{print $1}’
31. What is the name of DNS rpm package?
Answer: bind
32. What is the difference between nslookup and dig commands?
33. How to check your user id and group id?
Answer: id
34. How to check a file’s permission?
Answer: ls –l
35. What is the difference between “kill” and “kill -9” command?
36. What is subnet?
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?
Answer: tar (compress) the entire /etc directory and ftp
38. What is root home directory?
Answer: /root
39. What is rsyslogd deamon and its purpose?
40. Your company has terminated a server administrator. What is first thing as an administrator you should do to enhance the security?
Answer: Change root password
41. How to check the computer name or host name in Linux?
Answer: hostname
42. Which permission allows a user to run an executable with the permissions of the owner of that file?
Answer: First 3 bits should have x
43. What is the command to untar a tarred file?
Answer: untar
44. What is /proc directory used for?
45. What is the purpose of nsswitch.conf file
Answer: It tells the system where to go to resolve hostnames
46. List 3 basic commands to navigate the filesystem?
Answer: cd, pwd and ls
47. Which service/daemon should be running on the server that allows you to connect remotely?
Answer: sshd
48. What is the purpose of firewall?
49. List any 3 IT components?
Answer: Hardware, OS and Applications
50. Which directory has all the commands we use, e.g. ls, cd etc.?
Answer: /usr/bin or /bin
51. What is the difference between memory, virtual memory and cache?
52. Which of the following is correct?

  •  Hardware  Operating System  Users
  • Operating System  Users  Hardware
  • Database  Hardware  Users

53. Which of the following is a communication command?

  • grep
  • mail
  • touch
  • cd

54. How to rename a file or directory?
Answer: mv
55. How to change a hostname in Linux?
56. How to check network interfaces in Linux?
Answer: ifconfig
57. Why is “tail –f logfilename” command used most often and what does it do?
Answer: It will output all incoming logs in real time
58. What type of hardware have you worked on?
Answer: You should get yourself familiar with Dell, HP and UCS hardware by going online and check the vendor websites
59. How to sort a file in reverse order?
Answer: cat filename | sort –r
60. What is the name of operating system that runs Unix?
Answer: Solaris, HP-UX etc.
61. List all byte sizes from smallest to largest?
62. How to check the total number of partition in Linux?
Answer: fdisk -l
63. How to access a linux system from a linux system?
Answer: ssh
64. Explain the procedure of bonding 2 NICs or interfaces together?
65. What is the exact command syntax to list the 5th column of a file and cut the first 3 letters?
Answer: cat filename | awk ‘{print $5}’ | cut –c1-3
66. What is /etc/hosts file used for?
Answer: To resolve hostnames with IP address
67. List any 3 options of ‘df’ command and what they are used for?
68. What is the command to change file/directory permissions?
Answer: chmod
69. What is the purpose of pipe (|)?
Answer: To combine multiple commands
70. What is /etc directory used for?
Answer: For configuration files
71. Which command is used to list files in a directory?
Answer: ls –l
72. There is a command which gives you information about other commands, please explain that command and what is it used for?
Answer: man
73. How to delete a file and a directory?
Answer: rm filename and rmdir dirname
74. What is the difference between “tail” and “tail -10”?
Answer: None
75. List 4 commands to display or read a file contents?
Answer: cat, more, less, vi
76. Which command is used to read the top 5 lines of a file?
Answer: head -5 filename
77. What are the different commands or methods to write to a file?
Answer: echo > filename and vi filename
78. What is swap space and how to check swap space?
79. What is inode and how to find an inode of a file?
80. Which file to edit for kernel tuning?
81. What is the latest version of Redhat?
82. Name the command to find specific word from a file?
Answer: grep word filename
83. 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

84. How to check system hardware information?
Answer: dmidecode
85. How to check network interface MAC address?
Answer: ifconfig
86. If I don’t want others to read my file1, how to do that?
Answer: Remove r from the last 3 bits of file permission
87. What is the purpose of “uniq” and “sed” command?
88. 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?
Answer: ls –ltr
89. What is the difference between tar, gzip and gunzip?
90. What are the different ways to install and OS?
Answer: DVD, DVD iso and network boot
91. How to view difference between two files?
Answer: diff file1 and file2
92. 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

93. How to check Redhat version release?
Answer: uname –a or /etc/redhat-release
94. What is the difference between TCP and UDP?
95. What is a zombie process?
96. How do you search for a pattern/word in a file and then replace it in an entire file?
Answer: sed command
97. Explain the purpose of “touch” command?
Answer: To create an empty file
98. If a command hangs, how to stop it and get the prompt back?
Answer: Ctrl C
99. Which command is used to count words or lines?
Answer: wc
100. How to check the number of users logged in?
Answer: who
101. What is the command to view the calendar of 2011?
Answer: cal 2011
102. Which command is used to view disk space?
Answer: df –h
103. How to create a new group in Linux?
Answer: groupadd
104. What is the command to send a message to everyone who is logged into the system?
Answer: wall
105. Which command is used to check total number of disks?
Answer: fdisk –l
106. What is an mail server record in DNS?
Answer: MX
107. What does the following command line do?
Answer: ps -ef | awk ‘{print $1}’ | sort | uniq
List the first column of all running processes, sort them and remove duplicates
108. You get a call that when a user goes to 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

109. List 4 different directories in /?
Answer: /etc, /bin, /tmp, /home
110. What is the output of the following command:
Answer: $tail -10 filename | head -1
It will show the first line from the last 10 lines of a file
111. What are the different fields in /etc/passwd file?
112. Which command is used to list the processes?
Answer: ps –ef
113. What is the difference between “hostname” and “uname” commands?
Answer: Hostname will give you system name and uname will give you OS information
114. How to check system load?
Answer: top and uptime command
115. How to schedule jobs?
Answer: crontab and at
116. What is the 3rd field when setting up crontab?
Answer: Day of the month
117. What is the command to create a new user?
Answer: useradd
118. What is the “init #” for system reboot?
Answer: 6
119. How to restart a service?
Answer: systemctl restart servicename
120. How to shutdown a system?
Answer: shutdown or init 0
121. What is “ftp” command used for?
Answer: To transfer files from one computer to another
122. Explain cron job syntax? First is minute, second is..?
Answer: Min, house, day of the month, month, day of the week and command
123. How to delete a package in Linux?
Answer: rpm –e packagename
124. What is the file name where user password information is saved?
Answer: /etc/shadow
125. Which command you would use to find the location of chmod command?
Answer: which chmod
126. Which command is used to check if the other computer is online?
Answer: ping other computer
127. Please explain about LAN, MAN and WAN?
128. How to list hidden files in a directory?
Answer: ls –la
129. What is the difference between telnet and ssh?
Answer: ssh is secure where telnet is not
130. How to run a calculator on Linux and exit out of it?
Answer: bc and quit
131. List any 4 commands to monitor system?
Answer: top, df –h, iostat, dmesg
132. 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

133. What is difference between static and DHCP IP?
134. How to write in vi editor mode?
Answer: i = insert, a = insert in next space, o = insert in new line
135. What is the difference between “crontab” and “at” jobs?
Answer: crontab is for repetitive jobs where at is for one time job
136. What is vCenter server in VMWare?
137. What is “dmidecode” command used for?
Answer: To get system information
138. What is the difference between SAN and NAS?
139. What is the location of system logs? E.g. messages
Answer: /var/log directory
140. How to setup an alias and what is it used for?
Answer: alias aliasname=”command”
It is used to created short-cuts for long commands
141. What is the purpose of “netstat” command?
142. What are terminal control keys, list any 3?
Answer: Crtl C, D and Z
143. Which command(s) you would run if you need to find out how many processes are running on your system?
Answer: ps –ef | wc –l
144. What are the different types of shells?
Answer: sh, bash, ksh, csh etc.
145. How to delete a line when in vi editor mode?
Answer: dd
146. Which is the core of the operating system?
a) Shell
b) Kernel
c) Commands
d) Script
147. Which among the following interacts directly with system hardware?
a) Shell
b) Commands
c) Kernel
d) Applications
148. How to save and quit from vi editor?
Answer: Shift ZZ or :wq!
149. What is the difference between a process and daemon?
150. What is the process or daemon name for NTP?
Answer: ntpd
151. What are a few commands you would run if your system is running slow?
Answer: top, iostat, df –h, netstat etc.
152. How to install a package in Redhat Linux?
yum install packagename
153. What is the difference between “ifconfig” and “ipconfig” commands?
Answer: ifconfig for Linux and ipconfig for Windows
154. What is the first line written in a shell script?
Answer: Define shell
e.g. #!/bin/bash
155. Where is the network (Ethernet) file located, please provide exact directory location and file name?
Answer: /etc/sysconfig/network-scripts/ifcfg-nic
156. Why do we use “last” command?
Answer: To see who has logged in the system whether active or logged off
157. What is RHEL Linux stands for?
158. To view your command history, which command is used and how torun a specific command?
Answer: history and history #
159. What is NTP and briefly explain how does it work and where is theconfig files and related commands of NTP?
160. How to disable firewall in Linux?
161. How to configure mail server relay for sendmail service?
Answer: Edit /etc/mail/ file and add SMART_HOST entry
162. Where is samba log file located?
Answer: /var/log/samba
163. What is mkfs command used for?
Answer: To create a new filesystem
164. If you create a new group, which file does it get created in?
165. Which file has DNS server information (e.g. DNS resolution)?
Answer: /etc/resolv.conf
166. What are the commands you would run if you need to find out the version and build date of a package (e.g. http)?
Answer: rpm –qi http
167. On the file permissions? What are the first 3 bits for and who is it for?
Answer: Read, write and execute. They are used for the owner of the file
168. How to create a soft link?
Answer: ln –s
169. How to write a script to delete messages in a log file older than 30 days automatically?
170. How to quit out of “man” command?
Answer: q
171. Which command is used to partition disk in Linux?
Answer: fdisk
172. What is the difference between “shutdown” and “halt” command?
173. What is the exact syntax of mounting NFS share on a client and also how to un-mount?
174. What experience do you have with scripting, explain?
Answer: if-the, do-while, case, for loop scripts
175. How to get information on all the packages installed on the system?
Answer: rpm –qa
176. Explain VMWare?
177. 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?
Answer: grep for error, warning, failure etc. in /var/log/messages file
178. What is /etc/fstab file and explain each column of this file?
179. What the latest version of Windows server?
180. What is the exact command to list only the first 2 lines of history output?
Answer: history | head -2
181. How to upgrade Linux from 7.3 to 7.4?
Answer: yum install update
182. How to tell which shell you are in or running?
Answer: $0
183. 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?
Answer: – – – – – – – r – x
184. What is CNAME record in DNS?
Answer: Entry for hostname to hostname
185. What is the name of VMWare operating system?
Answer: ESXi
186. What is the client name used to connect to ESXi or vCenter server?
Answer: vSphere client
187. 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?
Answer: Give write permission on the first 3 bits
188. What is the latest version of VMWare?
189. What is the name of firewall daemon in Linux?

Answer: firewalld
190. Which command syntax you can use to list only the 20th line of a file?
191. What is the difference between run level 3 and 5?
Answer: 3 = Boot system with networking, 5 = boot system with networking and GUI
192. List a few commands that are used in troubleshooting network related issue?
Answer: netstat, tcpdump etc.
193. What is the difference between domain and nameserver?
194. 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?
Answer: more or less
195. How to start a new shell. E.g. start a new ksh shell?
Answer: Simply type ksh, or bash
196. How to kill a process?
Answer: kill processID
197. How to check scheduled jobs?
Answer: crontab –l
198. How to check system memory and CPU usage?
Answer: free and top
199. Which utility could you use to repair the corrupted file system?
Answer: fsck
200. What is the command to make a service start at boot?
Answer: systemctl enable servicename
201. 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
Answer: cat fileA >> fileB
202. What is echo command used for?
Answer: To output to a screen
203. What does the following command do?
Answer: 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”
204. Which file to modify to allow users to run root commands
Answer: /etc/sudoers
205. 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”
206. 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?
Answer: The /boot file is most likely corrupted

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