Linux Interview Questions and Answer

What do the following commands do and how would you use them?
tee
awk
tr
cut
tac
curl
wget
watch
head
tail
less
cat
touch
sar
netstat
tcpdump
lsof
What does an & after a command do?
What does & disown after a command do?
What is a packet filter and how does it work?
What is Virtual Memory?
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 a Split-Horizon DNS?
What is the sticky bit?
What does the immutable bit do to a file?
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?
How to 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 are the steps to add a user to a system without using useradd/adduser?
What is MAJOR and MINOR numbers of special files?
Describe the mknod command and when you’d use it.
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?
Explain briefly each one of the process states.
How to know which process listens on a specific port?
What is a zombie process and what could be the cause of it?
You run a bash script and you want to see its output on your terminal and save it to a file at the same time. How could you do it?
Explain what echo “1” > /proc/sys/net/ipv4/ip_forward does.
Describe briefly the steps you need to take in order to create and install a valid certificate for the site https://foo.example.com.
Can you have several HTTPS virtual hosts sharing the same IP?
What is a wildcard certificate?
Which Linux file types do you know?
What is the difference between a process and a thread? And parent and child processes after a fork system call?
What is the difference between exec and fork?
What is “nohup” used for?
What is the difference between these two commands?
myvar=hello
export myvar=hello
How many NTP servers would you configure in your local ntp.conf?
What does the column ‘reach’ mean in ntpq -p output?
You need to upgrade kernel at 100-1000 servers, how you would do this?
How can you get Host, Channel, ID, LUN of SCSI disk?
How can you limit process memory usage?
What is bash quick substitution/caret replace(^x^y)?
Do you know of any alternative shells? If so, have you used any?
What is a tarpipe (or, how would you go about copying everything, including hardlinks and special files, from one server to another)?
How can you tell if the httpd package was already installed?
How can you list the contents of a package?
How can you determine which package is better: openssh-server-5.3p1-118.1.el6_8.x86_64 or openssh-server-6.6p1-1.el6.x86_64 ?
Can you explain to me the difference between block based, and object based storage?

I’m Rajesh Kumar, a DevOps, SRE, DevSecOps, Cloud, and Platform Engineering expert passionate about sharing practical knowledge, real-world experiences, and industry best practices. I have worked at Cotocus and regularly write about technology, travel, investing, health, product reviews, and digital marketing through my various platforms.

I publish technical articles at DevOps School, travel stories at Holiday Landmark, stock market insights at Stocks Mantra, health and fitness guidance at My Medic Plus, product reviews at TrueReviewNow, and SEO and digital marketing strategies at Wizbrand.