Linux Administrator Interview Questions and Answers for Freshers & Experianced

By | December 24, 2013

Here are a list of linux administrator interview questions and answers that can help you crack interviews. We are listing questions and answers for both freshers and experienced. The list has questions asked at Wipro technologies, TCS, CSS CORP, Polaris and few others. If you are a linux admin, you can also help and support the community by adding the questions you faced or the questions you generally ask in an interview. So, here is my list.

These are some of the questions I and some of my friends faced. These are real time questions and a well prepared candidate should definitely be able to answers most of these questions. In this article, I will do my best to explain the concepts behind every question. In the mean while, I will also post some links that can help you answer the questions mentioned here. So here we go..

Note: This article needs to be updated. Check the existing questions until we are completely done with answers.

Linux Administrator Interview Questions and Answers

These are some of the questions my friend was asked at CSS CORP.

Que:1: How do you monitor or measure performance of a Linux server which is running for more than 5 years with out a break?

Ans: These are the commands that can help.

top, sar, vmstat, iostat, free

More detailed explanation of about these commands is here.

Que:2: Explain how DNS works, and talk about DNS Table?

Ans: This video here gives you the basic understanding of DNS. However, you should check this article here to understand the theory part better. More about DNS tables is explained here.

Ques:3: Talk about the boot process?

Ans: Boot process follows 6 major steps. Starting with BIOS > MBR > GRUB > KERNEL > INIT > RUN LEVELS

This image here (taken from the geek stuff) should give you a better idea. linux-boot-process

Ques:4: Explain the concept behind BIND and tell us how it works?

Ans: Coming  soon!

Ques:5: How do you monitor the status of an application that’s running on a Linux box?

Ans: Coming  soon!

TCS Linux Administrator Interview QUESTIONS and ANSWERS

Ques:6: How to Check Performance of Server? (Linux commands)

Ans: Coming  soon!

Ques:7: Command to check the total hardware in system?

Ans: Coming  soon!

Ques:8: Increase the size of lvm disk? (Command)

Ans: Coming  soon!

Ques:9: What is the ibm server console and how to work with it?

Ans: Coming  soon!

Ques:10: System down, how do you debug?

Ans: Coming  soon!

Ques:11: How to check disk performance, command?

Ans: Coming  soon!

Ques:12: How do you check the health of the hard disk?

Ans: Coming  soon!

Ques:13: Command to find bad sectors in hard disk?

Ans: Coming  soon!

Ques:14: ls command not working (showing io error) what do you do, how to debug?

Ans: Coming  soon!

Ques:15: How do you debug when the system is taking long time to authenticate or logging into server?

Ans: Coming  soon!

Wipro Technologies Linux Admin Questions and Answers:

Que:16: How do you restart network red hat? (freshers)

Ans: service network restart

Que:17: What are the types of red hat installation? I mean, what are the ways to install a Red Hat Server?\

Ans: So, red hat can be installed in many ways.

1: Installing through DVD or CD installation.

Any other modes (Network, raid and others) of installation requires usage of askmethod.

2: Network Installation with Networking.

–>  Download iso dvd on a network server.

–> Mount ISO file on webserver directory, so that it can be accessed via http.

mount -t iso9660 -o loop redhat-source.iso /srv/www/domain.com/RH (Enable directory browsing)

–> Create boot cd-rom using http://ip-of-network-server/RH/images/boot.img and boot using that or you can use Red hat dvd to boot.

–> Use ‘linux askmethod text’ at beginning to prompt us a method of installation which also includes network installation using http. FTP, NFS, Hard Drive and DVD-ROM installations are available too.

–> When promoted, select the HTTP install and include the directory path of the iso image http://ip-of-network-server/RH/

–> The installation should start normally from here on.

3: Network Installation with RAID5.

–>  Download iso dvd on a network server.

–> Mount ISO file on webserver directory, so that it can be accessed via http.

mount -t iso9660 -o loop redhat-source.iso /srv/www/domain.com/RH (Enable directory browsing)

–> Needs 3 hard drives.

–> While booting, type in ‘linux askmethod’ to ask for a method of installation.

–> Since we have image on http, we select http when it prompts for method of installation. (RAID installation via network)

–> Create a software raid partition on all 3 / more disks individually. Now, create a raid device (/dev/md0) using the three software raid partitions available. And make the mount point of that raid device as root partion (/).

–> Now continue the installation normally to bring a server up and running on a raid device.

4: LVM Network Installation.

–>  Download iso dvd on a network server.

–> Mount ISO file on webserver directory, so that it can be accessed via http.

mount -t iso9660 -o loop redhat-source.iso /srv/www/domain.com/RH (Enable directory browsing)

–> As mentioned above, use http://ip-of-network-server/RH/images/boot.img to boot the system and while booting, type in ‘linux askmethod’ to ask for a method of installation.

–> Select HTTP network installation and specify the location where the installation source is available.

–> Create a boot partition with 100MB of memory, using the /dev/sda disk and create physical volumes with the rest of the disk space available on /dev/sda. Create two other physical volumes with other two disks available.

–> Now, create a logical volume associated with a group.  Create separate partition for separate logical volumes. This screenshot shows 60G logical volume allocated for root partition. Do the same for /home/, /var/ /swap/, /tmp/ and others.

–> Once done, you can click on next to step in for next level of installation.

5: Kickstart Install

–>  Download iso dvd on a network server.

–> Mount ISO file on webserver directory, so that it can be accessed via http.

mount -t iso9660 -o loop redhat-source.iso /srv/www/domain.com/RH (Enable directory browsing)

– -> Use system-config-kickstart to create a kickstart file. Save it as “anaconda-ks.cfg” and publish it to http root directory of the iso image.

–> During install, in the main menu use the following…

‘linux ks=http://ip-of-server/anaconda-ks.cfg’

–> If the kickstart file is created properly and placed at the right location, the installation process should go on without any halt.

6: FTP Install

–>  Download iso dvd on a network server.

–> Mount ISO file on webserver directory, so that it can be accessed via http.

mount -t iso9660 -o loop redhat-source.iso /srv/www/domain.com/RH (Enable directory browsing)

–> To initiate the ftp install, its important to create a user without shell access for security reasons. You should also set the root directory of the user to the http directory where the linux iso image is mounted. This can be done using the following command. Please note that the user we are adding is ‘installuser’

useradd -s /bin/false -d /srv/www/domain.com installuser

Once user is added, use passwd command to set a password.

Use http://ip-of-network-server/RH/images/boot.img to boot the system and while booting, type in ‘linux askmethod’ to ask for a method of installation.

select ftp when prompted, and select location of server when asked for “ftp sitename”. After that when prompted, enter username and password of ftp server. Once entered, the installation is carried normally provided there is not network issues.

Que:18: How to  add a new Service to the Startup?

Ans: Using chkconfig command should help you add a new service to startup. Note that the service must be installed before using the command.

chkconfig –add iptables

To check the status, use the following command.

chkconfig –list | grep iptables

Use the following command to remove the service.
chkconfig –del iptables

This article here has more practice examples for chkconfig.

Que:19: How do you find the release version in linux red hat?

Ans: In red hat enterprise 5, check the file (/etc/redhat-release).  (I failed to answer this one in the interview.)

Can you explain the difference between, ext2 and ext3 file system?

Que:20: What are the codenames of Red Hat Enterprise Linux 5 and 6?

Ans: Red Hat EL5 is codenamed ‘Tikanga’ and Reh Hat EL6 is named ‘Santiago’.  Red Hat Enterprise Linux 7 (future version) is named – ‘Maipo’.

Polaris Linux Administrator Questions and Answers:

Ques:21: Tell me the booting process in Linux?

Ans: Verify Ques:3: 

Ques:22: lvm–> How to create logical volume and how to resize?

Ans: Coming  soon!

Ques:23: Shell program to remove all files older than 3 months.

Ans: Coming  soon!

Symantec Linux Admin Interview Question

Ques:24: How do you reset the root password of linux server?

Ans: Coming  soon!

Ques:25: How do you start linux red hat 5 in rescue mode?

Ans: At the beginning of the boot, use [F5] functional key to use Linux rescue mode.

Ques:26: How do you start a service on boot as default?

Ques:27: How to check the status of CRON JOBS? Are there any logs associated with it, if so what are they?

Ques:28: What is NFS? Explain.

Ques:29: How do you partition hard disk? Explain in detail.

Other possible interview questions and answers

Ques: How to display OS/Kernel information on a linux Redhat, Debian, Fedora, Ubuntu and CentOS?

Ans: use the command ‘uname -a’.  The command works on all the versions of Linux systems mentioned above.

Ques: How to find exact version of the kernel?

Ans: ‘uname -r’ displays kernel info with distribution info. Anything upto 3rd number is kernel version, and the rest is patched by the distributor.

[root myserver ~]# uname -r
3.12.6-34.EL

3.12.6 is the linux version. 3.12 is the major version and .6 being the minor version.

34.EL is patched by the distributor. EL stands for Enterprise Linux. Indicates the changes done by the distributor to the original version.

Ques: How do you mount iso image?

Ans: Here is the command. ‘mount -t iso9660 -o loop redhat-source.iso destination-directory’

Ques:  What is the significance of dev tree in linux (/dev/)?
Ans: /dev/ is a special directory that has special device files that can help accessing hardware devices connected to linux systems.

Ques: Explain in detail about disk Partitions?

Ans:  Disk Partitions – Check this to understand them.

Ques: Talk about inodes in linux.

Ans: Check this to understand inodes.

Ques: Difference between 32 bit and 64 bit OS?

Ans: These videos (this one and this one) should help.

Get started with bash shell scripting from here.

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