System Administrators -- DevOps -- Site Reliability Engineers -- Infrastructure Engineers
The majority of the questions were collected from:
- https://github.com/gurmeet1109/docgurmeet/tree/master/InterviewQuestionsSamples
- https://github.com/kylejohnson/linux-sysadmin-interview-questions/blob/master/test.md
- https://github.com/chassing/linux-sysadmin-interview-questions
- General Questions
- Simple Linux Questions
- Medium Linux Questions
- Hard Linux Questions
- Expert Linux Questions
- Networking Questions
- DevOp Questions
- Fun Questions
- Demo Time
- Other Great References
####[⬆] Contributors:
- What did you learn yesterday/this week?
- Talk about your preferred development/administration environment. (OS, Editor, Browsers, Tools etc.)
- Tell me about the last major Linux project you finished.
- Tell me about the biggest mistake you've made in [some recent time period] and how you would do it differently today. What did you learn from this experience?
- What function does DNS play on a network?
- What is HTTP?
- What is an HTTP proxy and how does it work?
- What is SMTP? Give the basic scenario of how a mail message is delivered via SMTP!
- What is RAID? What is RAID0, RAID1, RAID5, RAID10?
- What is a level 0 backup? What is an incremental backup?
- Describe the general file system hierarchy of a Linux system.
####[⬆] Simple Linux Questions:
- What is the name and the UID of the administrator user?
- How to list all files, including hidden one, in a directory?
- What is the Unix/Linux command to remove a directory and its contents?
- Which command will show you free/used memory? Does free memory exist on Linux?
- How to search for the string "my konfi is the best" in files of a directory recursively?
- How to connect to a remote server or what is SSH?
- How to get all environment variables and how can you use them?
- I get "command not found" for
ifconfig -a. What can be wrong? - What happens if I type TAB-TAB?
- What command will show the available disk space on the Unix/Linux system?
- What command is used to lookup DNS records?
- What Unix/Linux commands will alter a files ownership, files permissions?
- What does
chmod +x FILENAMEdo? - What does the permission 0750 on a file mean?
- What does the permission 0750 on a directory mean?
- How to add a new system user without login permissions?
- How to add/remove a group from a user?
- What is a bash alias?
- How do you set the mail address of the root/a user?
- What does CTRL-c do?
- What is in /etc/services?
- How to redirect STDOUT and STDERR in bash? (> /dev/null 2>&1)
- What is the difference between UNIX and Linux
- What is the difference between Telnet and SSH?
- Explain the three load averages and what do they indicate
####[⬆] Medium Linux Questions:
- What do the following commands do?
teeawktrcuttaccurlwgetwatchtail- What does a
&after a command do? - What does
& disownafter a command do? - What is a packet filter and how does it work?
- What is swap and what is it used for?
- What is an A record, an NS record, a PTR record, a CNAME record, an MX record?
- Are there any other RRs and what are they used for?
- What is the sticky bit?
- What is the difference between hardlinks and symlinks? What happens when you remove the source to a symlink/hardlink?
- What is an inode and what fields are stored in an inode?
- Howto force/trigger a file system check on next reboot?
- What is SNMP and what is it used for?
- What is a runlevel and how to get the current runlevel?
- What is SSH port forwarding?
- What is the difference between local and remote port forwarding?
- What steps to add a user to a system without using useradd/adduser?
- What is MAJOR and MINOR numbers of special files?
- Describe a scenario when you get a "filesystem is full" error, but 'df' shows there is free space.
- Describe a scenario when deleting a file, but 'df' not showing the space being freed.
- Describe how 'ps' works.
- What happens to a child process that dies and has no parent process to wait for it and what’s bad about this?
- How to know which process listens on a specific port?
- What is the difference between processes and threads?
- What is a tunnel and how you can bypass a http proxy?
- What is the difference between IDS and IPS?
- What shortcuts do you use on a regular basis?
- What is the Linux Standard Base?
- What is an atomic operation?
- Your freshly configured http server is not running after a restart, what can you do?
- What kind of keys are in ~/.ssh/authorized_keys and what it is this file used for?
- I've added my public ssh key into authorized_keys but I'm still getting a password prompt, what can be wrong?
- Did you ever create RPM's, DEB's or solaris pkg's?
- What does
:(){ :|:& };:do on your system and why you would care about that? - How trace system call and signal?
- What's happening when the Linux kernel is starting the OOM killer, how does it choose which process to kill first.
- Describe the linux boot process with as much detail as possible, starting from when the system is powered on and ending when you get a prompt.
- What's a chroot jail?
- When trying to umount a directory it says it's busy, how to find out which PID holds the directory?
####[⬆] Expert Linux Questions:
- A running process gets
EAGAIN: Resource temporarily unavailableon reading a socket. How you can close this bad socket/file descriptor without killing the process?
- What is localhost and why would
ping localhostfail? - What is the similarity between "ping" & "traceroute" ? How is traceroute able to find the hops.
- What command is used to show all open ports and/or socket connections on a machine?
- Is 300.168.0.123 a valid IPv4 address?
- Which IP ranges/subnets are "private" or "non-routable" (RFC 1918)?
- What is a VLAN?
- What is ARP and what is it used for?
- What is the difference between TCP and UDP?
- What is the purpose of a default gateway?
- What command is used to show the route table for a machine?
- A TCP connection on a network can be uniquely defined by 4 things. What are those things?
- When a client running a web browser connects to a web server, what is the source port and what is the destination port of the connection?
- How do you add an IPv6 address to a specific interface?
- You have added an IPv4 and IPv6 address to interface eth0. A ping to the v4 address is working but a ping to the v6 address gives yout the response
sendmsg: operation not permitted. What could be wrong?
####[⬆] DevOp Questions:
- Can you describe your workflow when you create a script?
- What is GIT?
- What is a dynamically/statically linked file?
- What does "configure && make && make install"?
- What is puppet/chef/ansible used for?
- How do you create a new mysql user?
- How do you create a new postgres user?
- What is a virtual IP address? What is a cluster?
- How print the strings of printable characters in files?
- How look shared library dependencies?
- What is Automake and Autoconf?
- ./configure shows an error that libfoobar is missing on your system, how could you fix this, what could be wrong?
- Advantages/disadvantages of script vs compiled program.
- What is the difference between fork and thread? And parent and child process in fork system call?
- What's the relationship between continuous delivery and DevOps
- How is securing a cloud environment different than a hardware environment?
- How do you handle prioritizing your tasks when you're interrupted with ah-hoc issues?
- What are the important aspects of a system of continous integration and depolyment?
- How would you deal with the eventual consistency model that Amazon Web Services uses in the cloud model?
- Tell me about one of your favorite command line tools, such as nc, curl, tail, and something interesting that you'v done with that utility.
- How do you handle revision control?
- In Git, what's the difference between merge and rebase?
- Describe a pipeline for updating Apache to 100 cloud servers. How would that evolve for 1000 servers?
####[⬆] Fun Questions:
- A careless sysadmin executes the following command:
chmod 444 /bin/chmod- what do you do to fix this? - I've lost my root password, what can I do?
- I've rebooted a remote server but after 10 minutes I'm still not able to ssh into it, what can be wrong?
- If you were stuck on a desert island with only 5 command-line utilities, which would you choose?
- You come across a random computer and it appears to be a command console for the universe. What is the first thing you type?
- Tell me about a creative way that you've used SSH?
####[⬆] Demo Time:
- Unpack test.tar.gz without man pages or google.
- Remove all "*.pyc" files from testdir recursively?
- Search for "my konfu is the best" in all *.py files.
- Replace the occurrence of "my konfu is the best" with "I'm a linux jedi master" in all *.txt files.
⁉️ more on files ... cut, tr, awk ...- Test if port 443 on a machine with IP address X.X.X.X is reachable.
- Get http://myinternal.webserver.local/test.html via telnet.
- How to send an email without a mail client, just on the command line?
- Write a
get_primmethod in python/perl/bash/pseudo. - Find all files which have been accessed within the last 30 days.
- Explain the following command
(date ; ps -ef | awk ‘{print $1}’ | sort | uniq | wc -l ) >> Activity.log - Write a script to list all the differences between two directories.
- Write a program in any language you choose, to reverse a file.
- In a log file with contents as
<TIME> : [MESSAGE] : [ERROR_NO] - Human readable textdisplay summary/count of specific error numbers that occured every hour or a specific hour
####[⬆] Other Great References:
Some questions are 'borrowed' from other great references like:
- https://github.com/darcyclarke/Front-end-Developer-Interview-Questions
- https://github.com/kylejohnson/linux-sysadmin-interview-questions/blob/master/test.md
- https://github.com/gurmeet1109/docgurmeet/tree/master/InterviewQuestionsSamples
- http://slideshare.net/kavyasri790693/linux-admin-interview-questions