DevOps Linux Interview Answers
Linux Interview Questions
1 How many flavours of Linux you have worked on?
Ans Ubuntu, Debian, RHEL, Fedora, Kali Linux, CentOS etc..
2 What is a difference between hard link and soft link.
Ans Hardlink - ln , same properties as linked files, inode number is same , even if original file is deleted we can access link
Softlink - ln-s, not same properties as linked files, inode number is different , utilize less space, if original file is deleted we cannot access link
3 Can you explain Linux directory structure.
Ans Starting from the root
/bin /dev /etc /usr /home /lib /sbin /tmp /var/
1: bin- contains all executables for many shell commands like cp,cd and many more
2: dev- Contains special files, including those related to devices like this are virtual devices and not physical devices on disk.
3: etc- contains configuration files of system. mostly used by admin for password files and networking files. if you want to change system config come here.
4: usr- container all executalbe file, libraries, source of most of the system programs.
again usr is divided into sub commands like:
/usr/bin: contains basic user commands
/usr/sbin: containes additional commands for admin
/usr/share: contains documents to all libraries
5: home- contais personal directories of specific users.
example if you create to user ram and shyam: there location will be: /home/ram & /home/shyam
6: lib- contains codes and executable binaries.
7: sbin- contains system binaries
8: tmp- directory holds temoporary files. temprary means when system restarts all files are gone/deleted.
9: var- contains program runtime info like logging, user track, caches, here files are not deleted automatically because its crucial info like logs history of sytem.
10: mnt- used by sys admin to mount and add new filsystem
11: proc- contains info about current running process and kernel.
12: media- points to removable disks, like usb, sd card, etc
13: srv- contains services provided by system. for ex: http server
4 What is the home directory of root user.
Ans /root
5 Command to check whether specific port is enabled or not.
Ans netstat -tuln | grep :port_number
lsof -i :port_number
nmap -p port_number localhost
6 What are daemon services in Linux.
Ans Daemon simply means background processes that runs continuously in Linux, like cron jobs.
7 How can you provide root privileges to any user.
Ans add user in /etc/sudoers file using Visudo
8 How would you check the current running processes on a Linux system?
Ans ps aux, ps -ef , htop
9 Explain the concept of file ownership in Linux and how it relates to permissions.
Ans So when the file is create the user who created file has full control on it.
if a file is assigned to a group all users in that group share the same permissions.
you can do ls -la to see permission of file. and ls -l filename to see ownership
ls -l filename command will give you owner name group name etc info.
so when a Alice user create a file named demo.txt he had read write permission and group and others had read only permission.
permission for normal file: for user read and write
for group only read
for others only read
permission for executable file: for user read and write
for group only read
for others only read
we need to make file executable manually like
chmod u+x filename
if you want to change owner of file:
sudo chown bob demo.sh just an example demo.sh ownership is change to bob.
read r - 4
write w - 2
execute x - 1
chmod 777 devops.txt - read , write and execute permissions to user, group and others
10) Describe the process of setting up passwordless SSH between two Linux systems.
Ans) ssh-keygen -t rsa -b 4096 in one server
copy public key to another server
sudo nano /etc/ssh/sshd_config in same server where you copied key
Set PasswordAuthentication no
restart sshd service
11) How would you manage system updates and patches on Linux servers.
Ans) for ubuntu based os
update package -- sudo apt update
upgrade all packages -- sudo apt upgrade -y
remove old packages -- sudo apt autoremove -y
check updated logs -- car /var/log/apt/history.log
reboot if required -- sudo reboot
12) How would you regain access of Linux server if key is lost.
Ans) Stop the instance (don’t terminate it).
Detach the root volume from the instance.
Attach the volume to another instance that you can access.
Once attached, mount the volume on the new instance and navigate to the ~/.ssh/authorized_keys file of the root (or relevant) user on the attached volume.
Add your new SSH key to the authorized_keys file.
Detach the volume from the second instance and reattach it to the original instance as the root volume.Start the instance again and log in using the new SSH key
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