The Linux administration interview will test your knowledge of operating systems and also your ability to think and sometimes act like an individual tasked with managing systems, troubleshooting problems like a system administrator, securing systems like an information security engineer and programming to automate processes like an application developer.
As a Linux administrator you are responsible for ensuring that servers are stable, secure, high-performance and available 24/7. The purpose of this guide is to prepare you for an interview in a rigorous manner and provide you with examples of scenarios you may encounter during an interview or during your real-world Linux admin experience.
This blog will provide you with examples of the types of interview questions you will face as well as practical answers to those questions to enable you to present yourself to the interviewer as someone who is confident, clear and knowledgeable about systems at a system level.
Linux is an open-source operating system designed for high reliability, high security, and high levels of flexibility and performance in a variety of applications. High tech companies use Linux for their server hosts, cloud infrastructure, virtualization, containers, databases, networking, and automation tools because of its proven ability to manage resources and provide a solid level of uptime at all times, compared to other operating systems available.
Linux administrators are responsible for managing all aspects of the server infrastructure, users, security, backups, patches, installations, networking, system performance, and automating daily processes. A Linux Admin is responsible for installing the operating system and/or services, configuring the operating system and/or services, monitoring for errors or anomalous events, troubleshooting system outages, overtime servers, and maintaining system security.
Initially the BIOS/UEFI initializes the computer's hardware then the bootloader (GRUB or LILO) loads the kernel into memory after reading configuration information about Linux. Once loaded, the kernel prepares the machine for use by initializing all of its hardware drivers and starting the init (or systemd) process that starts the services configured to run at boot. If you know what happens at each stage of the boot process you will be able to determine if something went wrong during the startup process of a Linux system.
The kernel is the core component of the operating system; it communicates with the physical hardware and manages system resources. While the kernel is how the operating system interacts with the physical hardware, the shell provides a way for users to interact with the operating system using a command line interface.
As the superuser, the root user has total administrative control over a Linux operating system. The root user will be able to change any file in the computer (including system files), install or remove applications, manage users, and control any and all running services. Because of this level of access, the root user should always exercise caution when using the root account to avoid damaging the computer.
In a hierarchical format, Linux organizes its files in a specific manner, beginning with the root directory. There are many other directories in the Linux file system; directories that are commonly encountered are as follows: Bin - Contains binary code; ECT - Configuration files; Home - Users' home directories; Var - Log files; USR - Applications; Boot - Kernel images.
A hard link is essentially an alternate name or references for the original file. It points directly back to the original file's inode, so if the name of the original file is changed or deleted, the hard link continues to work because it still references the same inode.
A soft link (also known as a symbolic link), is simply a shortcut or reference to the original file path (as opposed to referencing the original file's inode). Therefore, if the original file is deleted, the soft link becomes broken or invalid.
An inode is a data structure that contains all of the metadata for a file including the file permissions, owner, file size, and timestamps, but does not contain the name of the file nor its actual data.
To check disk usage, you can use disk utilization commands to display current file system or disk partition usage and directory usage. Typically administrators will constantly monitor disk space and disk usage levels as a way to prevent their systems from failing due to reaching full utilization of the storage space.
The LVM enables flexible management of storage systems/disk storage. It allows for current and future resizing of disk/partition sizes, dynamic addition of new storage volumes, and creation of snapshots of the logical volumes without taking any downtime.
Linux manages permission through three different permission types: read, write, and execute. A single permission may be granted to one or all three of the classes; they are classified as owner, group, and other. The three classes of users determine who can access or modify a file or directory.
"chmod" is the command used to modify the permission on files. It is typically used to either grant or deny access to files/directories.
"chown" is the command used to change ownership of a file. System administrators will use that command to change the owner of files, often to ensure that files are assigned to appropriate user and/or groups.
The command "su" (Substitue user) allows the user running the command to change their user identity completely. In contrast, "sudo" (Super User Do) allows users to run specific commands with elevated privileges. The execution of commands with the elevated privileges via "sudo" creates System Audit Logs.
"/etc/passwd" is a system file that contains user account data including the user's name, User ID, home directory, and terminal.
A process refers to an instance of a Program currently being run. Every Process occupies System Resources and an process has a unique Process ID.
Performance monitoring is done with a variety of methods such as CPU, Memory, Disk and process activity. Continuous System Monitoring prevents crashes and bottlenecking.
Load average indicates the system load over a period of time and indicates how many processes are currently waiting for CPU resources.
kill sends a signal to kill a process gracefully, while kill -9 will stop a process without giving it an opportunity to cleanup.
Nice is a command that will start a process at a certain priority while renice is a command to change the priority of a process that is already running in order to manage how much CPU time is allocated to that process.
Network Administrators use various tools for that to check an IP address, routing and interface status.
DNS is used to convert a domain name to an IP address to allow two systems to communicate on a Network.
TCP is a guaranteed, connection-oriented protocol. Whereas UDP is an unconnected, fast protocol that does not guarantee delivery of packets.
When troubleshooting a network issue, you should start by checking all aspects of your network for Connectivity, Routing, DNS resolution, Firewall Rules and Service Availability.
SSH is an encrypted connection to provide a secure method for remote login and transferring data.
These are applications that will install, update, delete, and maintain all the software on your system automatically.
Apt and yum are both Package Managers, they are used in Linux to add new software, and to update existing software.
Updates are meant to fix security holes, increase system stability, and improve system performance.
A firewall is a device that regulates the flow of all incoming and outgoing information over a network between a host and other devices by applying predetermined rules to prevent unauthorized individuals from accessing a computer or any of its data.
SELinux is a security program that implements a security policy to regulate how processes access the files and resources on a computer.
Disabling the root account, Enforcing Password Strength, Using Firewalls, Keeping All the Parts of Your System Updated, Reviewing Your Logs and Preventing Access to Authorized Users Only.
fail2ban is an application that protects the server from anyone who may be trying to get into the server by automatically blocking their access.
is that it protects your important data from being lost because of failure of your computer hardware, corruption, and/or unintentional deletions.
A full backup, in which everything is copied.
An incremental backup in which you only copy anything that has changed since the most recent backup.
A differential backup, where only what has changed since the last full backup is copied.
Restoring a system means returning the system and its data to the last known good configuration of that system as of its last full backup.
Inspect your disk for its available space and how much is currently being used; delete files that you no longer need; rotate out the older logs; delete any temporary files; add an additional hard drive or solid-state disk.
Review the server's CPU usage; review the server's memory usage; examine the server's disk I/O utilization; review the server's running processes; and review your server logs for clues as to what may be causing the performance issue.
Verify that your computer is connected to the network; check to ensure that the SSH has started; check for any firewall settings that would block SSH traffic; check the proper configuration of the SSH on the server.
Verify that the server is active, review the logs and verify what services are operating, confirm that there is adequate storage available, check for network connectivity issues, and Verify that your app is in good condition.
Automate scheduled tasks, for example create, read, update, delete, backup or maintain.
Systemd is an init system in many Linux distributions to manage system processes and start the Operating System.
Log rotation reduces the amount of disk space that will be consumed by logs.
Swap memory is the space that is used on a hard disk when there is no more RAM available.
Kernel tuning is making adjustments to your systems parameters in order to improve performance.
Be prepared to explain concepts and processes clearly, support these explanations with examples from your own experiences, communicate a troubleshooting methodology that demonstrates your understanding of how the commands you used worked, and demonstrate an awareness of security issues. Interviewers are much more interested in how you came to a solution than in memorized answers.
Yes, There Is High Demand For Linux Administrators in Cloud Computing, DevOps, Cybersecurity, and Enterprise IT.
No, You Don't Need To Be an Expert Coder, but Having Knowledge Of Basic Scripts Will Help Automate Your Workload.
There Are Many Good Distros Available To You To Help You Develop Your Administration Skill Set.
You Should Work With Your Hands Every Day To Develop Your Confidence, and To Help Improve Your Troubleshooting Skills When Things Go Wrong In the Real World.
Yes, most Cloud computing is done on Linux servers.
The profession of being a Linux administrator represents a very strong and secure career choice. You will be challenged in your Interviews with practical problems requiring thought as well as knowledge. You need to be able to demonstrate an understanding of the system, an effective approach to troubleshooting, your ability to implement and maintain security, and your ability to automate processes within the system. If you prepare properly, get experience with hands on activities, and have the proper confidence, you will be able to pass the Linux Administrator interview process and succeed in establishing your career as a system administrator within the fields of cloud infrastructure and DevOps.
You will master how to use Linux properly, think like a System Administrator, and be assured of eventual success.
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