I've been in tech for a long time and have interviewed quite a bit from small to very large companies. All of the questions mentioned on this page are ones I have been asked for IT-related positions. Each time a question was asked, I'd write it down. I thought I would share these with all of you for those who are wanting to study for their next interview. Enjoy!

  • User says their internet is slow and that it takes ages to get to websites. What steps would you do to troubleshoot?
  • Tell me five ways to find the current date and time on a Linux system.
  • How would you delete a file called -f on a Linux system?
  • Can you explain the difference between a hub, a router, and a switch.
  • What are the layers of the OSI model and describe each one?
  • How would you find a device on a network?
  • How does traceroute work? How is it different from ping?
  • What is ping?
  • Draw an entire network (very broad, but will allow you to show everything you know about one)
  • What is DHCP? How does it work? What is assigned to the computer that requested an address?
  • What is ARP?
  • How does a switch work?
  • What are some ways you can kill a program that is not responding? (think of the command line as well)
  • On a Linux machine, how would you find the drive you just plugged in? How would you mount it?
  • With the kill command what does -9 do (kill -9)? How is it different than kill -11?
  • What is DNS?
  • On a mac, what are some ways you can transfer data from one computer to another?
  • What is the PRAM and SMC reset do? What do each reset?
  • Say that I opened my browser and went to www.google.com. Describe what exactly happens in order for the page to display in my browser? In detail: https://github.com/alex/what-happens-when
  • What is an inode? What metadata does it contain?
  • What is the difference between a hard link and a soft link (symlink)?
  • What is the Windows registry? How does linux do the same thing? Mac?
  • What is the bootup process of a machine of your choice?
  • What are the differences between 802.11 a,b,g, and n?
  • What is in an IP header? TCP Header?
  • What is the difference between a public IP and a private IP?
  • What port is SMTP? Is there more than one port used for SMTP?
  • What is an MX record?
  • Describe the TCP Handshake
  • What is the difference between TCP and UDP?
  • A user has a machine that shows no output on the monitor. How to you troubleshoot? How can you see the state of the boot sequence without replacing the graphics card?
  • How do you define the following types of malware: a worm, a trojan, a rootkit?
  • How are ICMP packets denoted in the IP header? How are ICMP echo and reply denoted?
  • What routing protocol do you think Google uses and why?
  • You have 2 linux machines. How would you copy host A's disk0 to host B's disk1 and verify it copied correctly?
  • A user with a Windows laptop says that whenever they try to visit a particular website they instead see some strange Russian website they're not expecting. How would you troubleshoot this?
  • In linux, you want to unmount a filesystem but it is in use. Can you fix this without rebooting the machine?
  • What is RAID? Describe RAID 0, 1, 5, 6, and 10
  • Your machine needs to send data to a host with an IP address on the same LAN. How does it specify the address the data should go to?
  • Be prepared to talk about any acronyms you mention
  • How do you start a website using Apache? Nginx?
  • You are a new consultant at a company and you are to give the company new internet. What up and down speeds would you provide and why?
  • What is OWFS?
  • What is Journaling? Why is it useful?
  • What is HTTPS? How does it work?
  • How do private and public keys work?
  • Does DNS use TCP or UDP? Why?
  • What is QoS?
  • What is a VLAN?
  • What is TLS?
  • What is ICMP?
  • What is a fork bomb?
  • How would you test if a port is open on a remote server?
  • You opened a port on a server, but from the outside, you cannot connect to that port. What might the problem be?
  • A fellow technician says that a Windows machine they're working on has an IP address of, and asks you to help him troubleshoot. What do you do?
  • What are IPTables? What are the different things you can do with them?
  • On a Linux machine, how can you spin up a webserver? What is a vhost? Where do the configuration files live?
  • Name a few HTTP requests.
  • List some ports and define what they are used for.
  • What command would you use to list the number of threads for a running process?
  • How would you find the system load average WITHOUT causing more load?
  • What are some of the default Linux system variables?
  • What is garbage collection?
  • Using bash, how would you output a specific column in a file?
  • What's the difference between bootp and DHCP?
  • What is Immutable Infrastructure? How does it differ from Mutable Infrastructure and what are some advantages of having an Immutable Infrastructure?
  • Name a few data structures.
  • What tool would you use to sniff DNS traffic?
  • What tool would you use to view disk IO?
  • What is a CDN?
  • What is Puppet, Ansible, Chef, Saltstack and what are they used for?

More questions: https://github.com/chassing/linux-sysadmin-interview-questions


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Joseph Ziegler

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