You could be a seasoned Linux Sys Admin and still get cold feet the night before an interview.
Applying for jobs is never easy. But it’s even harder to gear yourself up to face an interviewer, let alone a full panel of them, and answer questions in a way that demonstrates your capabilities.
This is especially true because of the importance of the role.
As Larry LaBas says, on Taos.com, ‘a good system administrator can mitigate or prevent issues like system breakdowns, software malfunctions and security breaches, making them a jack of all trades’. (Click To tweet)
Here’s a list of commonly-asked interview questions to help you get through the hiring process with confidence.
Popular skills for Linux System Administrators
- What is the core of the Linux OS?
This question is fairly basic, so apart from mentioning that the core is Kernel, you should also mention its component parts.
This would include Shell, Command, Script, and Terminal. Also add a brief explanation of what each component is.
- What is the difference between Linux and UNIX?
Here, you’ll have to remember to mention that Linux is based on UNIX, apart from the fact that it is an open source software, while UNIX is not.
- What is BASH?
You probably know that BASH is short for Bourne Again Shell. When interviewers ask you this, mention that Steve Bourne wrote it, and how it differs from the original shell.
If the interviewer asks you to elaborate further, you could talk about the differences between the BASH and DOS consoles.
- Explain the boot process of the Unix system
This is a fairly open-ended question, but as Allen Wittenauer points out, ‘open-ended questions are asked so you can demonstrate your familiarity and knowledge of the system’. (Click To Tweet)
When you answer this question, talk about the BIOS, MBR, LILO, and GRUB.
- What is your favourite shell and why?
Just about any platform discussing interview questions for Linux system administrators mentions this, including the list of questions to ask interviewees by Chander Shivdasani.
Whether you go with tcsh, csh, or BASH, make sure you’re clear on the features of all and are able to support your preference with facts and examples.
- What is the swap space?
The swap space is used by Linux to hold programmes that are running concurrently when the RAM runs out of space.
Discuss the different kinds of swap space, as well as the advantages and disadvantages of swapping when you’re answering this particular question.
- How do you change permission in Linux?
As Elvis Ibrahimi says, ‘changing permissions in Linux/Unix is something that you’re going to be doing on a daily basis, so you should be able to describe the process clearly and in as much detail as you can’.
Talk about the basic Read, Write, and Execute rights, using permission parameters, and describe how you can view the permissions of a file or folder.
- Discuss IPtables
This is a very important question that is commonly asked by interviewers, because as a system administrator, you’ll need to be very familiar with IPtables, the Linux firewall.
Describe the different policy chains used—the input, forward, and output chains. Mention how you would list and flush the IPtables, and how you would add rules to it.
- What is a zombie process?
You should be able to describe it as one where the child process is terminated before the parent process, leaving it running on the process table.
Also brush up on how you would resolve it, and if the resolution is even necessary, because this question crops up fairly often in interviews.
- List out the differences between Softlink and Hardlink
This is another common question most interviewers ask.
You should begin by describing both softlink and hardlink. Then, succinctly list out the differences in a few basic points like Bobbin Zachariah has in this article.
- Why is LVM required?
It’s a fairly simple answer. First, tell the interviewer that it stands for Logical Volume Manager.
Then, all you have to tell them is that you need an LVM partition in Linux if you want to resize a file system online.
- How to upgrade Kernel in Linux?
This one is a trick question, because you should never directly upgrade Linux Kernel.
Always install the new kernel using the rpm command. Also communicate to your interviewer that upgrading the existing kernel wrongly can send your Linux into an unbootable state.
- What are manifests in Puppet?
Start off by talking about the puppet server and how it’s an IT automation software that pushes configuration to its clients using code.
You can then tell them that Manifests in Puppet are the files in which client configuration is specified.
- How to change the default runlevel in Linux?
Begin by saying that you have to edit the file—/etc/inittab.
You’ll also have to tell the interviewer how to change the runlevel using the ‘init’ command. For example, ‘init 3’ will move the system to runlevel 3.
- What is the advantage of open source?
The best thing about open source is the fact that it allows people to create forks and distribute their own version of the software, leading to versatility.
People can then debug the code and make it run better before distributing it again. A greater number of people working on the code means that it’s more likely that bugs will be identified and squashed.
You should explain to your interviewer how open source benefits everyone involved.
- What are symbolic links?
You need to know that symbolic links are similar to shortcuts on Windows.
You can also tell your interviewer that they allow instant access to programs, files, and directories without having to go to the pathname.
- How do you share a program across different virtual desktops under Linux?
The answer to this is fairly straightforward. But break down the process by starting with the icon that looks like a pushpin on the upper left corner.
Tell them how pressing this button will “pin” that application in place, making it appear in all the virtual desktops, in the same position on screen.
- What are the kinds of permissions under Linux?
Speak about the 3 different kinds of permissions on Linux.
- Read: users can read the files or list the directory
- Write: users may write to the file or add new files to the directory
- Execute: users may run the file or lookup a specific file within a directory
- What could possibly be the problem when a command that was issued gave a different result from the last time it was used?
Explain how since Linux is case sensitive. The command in question was probably entered in a different format.
Cite an example of how you should type ‘ls’ to list all the files in a directory. Using ‘LS’ could produce a different result.
- How do you terminate an ongoing process?
Explain how every process in the system is identified by a unique process id or pid.
Using the ‘kill’ command followed by pid terminates that process. You can add a line on how to terminate all processes at once, by using kill 0.
- What are filenames that are preceded by a dot?
It’s basic knowledge that filenames that are preceded by a dot are hidden files.
You can tell your interviewer how these files may hold important data or setup info, and hiding them makes it less likely that they’ll get accidentally deleted.
- What are the different modes when using vi editor?
Remember, there are 3 modes under vi:
- Command mode: the mode you start in
- Edit mode: the mode that allows text editing
- Ex mode: the mode where you interact with vi to process a file
- What is redirection?
It’s a fairly simple process, allowing you to direct data from one output to another. You can also use it to direct an output as an input to another process.
- How do you insert comments in the command line prompt?
All you need to do is type the ‘#’ symbol before you type a piece of text. Explain to your interviewer how typing ‘#’ tells the shell to completely ignore what follows.
- Describe the root account
The root account is like a systems administrator account, and allows you full control of the system.
You can go on to explain how you can create and maintain user accounts, assigning different permissions for each account.
And there you have it. 25 of the most commonly asked interview questions for aspiring Linux system administrators.
With all the new methods of recruitment out there, you need to brush up on these questions to be able to handle the gruelling interview sessions that you may face.