20+ Linux System Administrator Interview Questions and Answers for Freshers

Possible causes of user not able to login to an application

• Incorrect username or password

• Account locked or disabled

• Expired password

• Network connectivity issues

• Application server down

• Incorrect permissions or access rights

• Firewall blocking access

• Authentication server issues

• Application configuration errors

A user can be created in a single line command using the 'useradd' command in Linux.

• Use the 'useradd' command followed by the username to create a user.

• Specify additional options like home directory, shell, etc. if required.

• Example: useradd john -m -s /bin/bash

A cron job is a scheduled task that runs automatically at specific intervals on a Linux system.

• Cron jobs are managed by the cron daemon, which reads a configuration file called crontab.

• To write a cron job, you need to edit the crontab file using the 'crontab' command.

• Each line in the crontab file represents a separate cron job and follows a specific format.

• The format consists of five fields: minute, hour, day of month, month, and day of week.

• You can use various symbols and op...read more

To set the password for a newly created user in Linux, use the 'passwd' command followed by the username.

• Open the terminal or SSH into the Linux system

• Run the 'passwd' command followed by the username of the new user

• Enter and confirm the new password when prompted

To reset the root password, you can use the single-user mode or a bootable Linux distribution.

• Boot into single-user mode by interrupting the boot process and appending 'init=/bin/bash' to the kernel command line.

• Remount the root filesystem as read-write using the 'mount -o remount,rw /' command.

• Change the root password using the 'passwd' command.

• Alternatively, boot from a bootable Linux distribution like a Live CD or USB and mount the root partition to reset the password.

Decommission is the process of retiring a system or service, while recommission is the process of bringing it back into service.

• Decommission involves shutting down and removing a system or service from operation.

• Recommission involves restoring a decommissioned system or service back into operation.

• Decommission and recommission are common processes in IT infrastructure management.

• Examples include retiring an old server and replacing it with a new one, or taking a website offli...read more

LVM (Logical Volume Manager) is a disk management tool used in Linux systems to manage storage devices and create logical volumes.

• LVM allows for easy management of storage by abstracting physical storage devices into logical volumes.

• It provides features like volume resizing, snapshots, and striping for improved performance and flexibility.

• LVM enables dynamic allocation of storage space, making it easier to add or remove storage devices without disrupting the system.

• It allows ...read more

NFS allows remote access to files and directories, providing centralized storage and easy sharing.

• Enables sharing of files and directories across multiple systems

• Reduces storage costs by centralizing data on a single server

• Improves data availability and reliability through redundancy

• Simplifies administration by allowing for centralized management

• Examples: Sharing files between a web server and a database server, sharing user home directories across a network

LVM (Logical Volume Manager) allows flexible disk management in Linux, enabling dynamic resizing and efficient storage allocation.

• LVM abstracts physical storage into logical volumes, allowing for easier management.

• It consists of Physical Volumes (PVs), Volume Groups (VGs), and Logical Volumes (LVs).

• Example: Create a PV with 'pvcreate /dev/sdb1', then a VG with 'vgcreate myvg /dev/sdb1'.

• Logical Volumes can be resized with commands like 'lvextend' and 'lvreduce'.

• LVM supports sn...read more

An I node number is a unique identifier assigned to each file in a Unix-like file system.

• I node number is also known as index node number.

• It contains metadata about the file such as ownership, permissions, timestamps, etc.

• It is used by the operating system to locate and access the file on the disk.

• The command 'ls -i' can be used to display the I node number of a file.

Hard links point to the same inode, while soft links (symlinks) point to the file name, allowing for different behaviors.

• Hard links share the same inode number, meaning they reference the same data on disk.

• Soft links (symlinks) are separate files that point to the original file's path.

• Deleting the original file does not affect hard links, but it breaks soft links.

• Example of hard link: 'ln file1.txt link_to_file1.txt'

• Example of soft link: 'ln -s file1.txt symlink_to_file1.txt'

The kernel is the core component of an operating system, managing hardware and software interactions.

• Acts as a bridge between applications and hardware.

• Manages system resources like CPU, memory, and I/O devices.

• Handles process management, including scheduling and multitasking.

• Provides system calls for applications to interact with hardware.

• Examples include Linux kernel, Windows NT kernel, and macOS XNU kernel.

Linux is an open-source operating system, while Windows is a proprietary operating system developed by Microsoft.

• Linux is open-source and free to use, while Windows is proprietary and requires a license.

• Linux is highly customizable and can be modified by users, while Windows has limited customization options.

• Linux is known for its stability and security, while Windows is more vulnerable to viruses and malware.

• Linux uses a command-line interface (CLI) as its primary interface,...read more

LVM (Logical Volume Manager) is a tool used to manage disk storage in Linux systems by creating logical volumes from physical volumes.

• LVM allows for dynamic resizing of logical volumes without the need to unmount the filesystem.

• It provides features like striping, mirroring, and snapshotting for better data management.

• Commands like pvcreate, vgcreate, lvcreate are used to create physical volumes, volume groups, and logical volumes respectively.

tar is a command-line utility used for archiving files and directories into a single file.

• Can be used to compress and decompress files

• Can preserve file permissions and ownership

• Can create and extract archives in various formats

• Commonly used with gzip and bzip2 for compression

• Example: tar -cvzf archive.tar.gz /path/to/directory

CTC stands for Cost to Company, which is the total salary package offered to an employee by the company.

• CTC includes salary, bonuses, benefits, and any other perks offered by the company.

• It is the total amount of money a company is willing to spend on an employee.

• CTC is often used as a benchmark to compare job offers from different companies.

DNS servers are responsible for translating domain names into IP addresses, enabling communication between devices on the internet.

• DNS servers store and manage a database of domain names and their corresponding IP addresses.

• They facilitate the process of resolving domain names to IP addresses, allowing devices to communicate with each other.

• DNS servers use a hierarchical structure, with root servers, top-level domain servers, and authoritative name servers.

• They support variou...read more

DNS server is a computer server that contains a database of public IP addresses and their associated hostnames.

• DNS stands for Domain Name System

• It translates domain names into IP addresses

• It helps in resolving internet requests

• Examples of DNS servers are Google DNS, OpenDNS, etc.

The Linux kernel is the core component of the Linux operating system, responsible for managing hardware resources and providing essential services.

• Manages hardware resources such as CPU, memory, and peripherals

• Provides essential services like process management, file system support, and networking

• Open-source and constantly updated by a community of developers

• Examples: Linux kernel versions 2.6, 3.0, 4.0, etc.

To add a user in Linux, use the 'useradd' command followed by the username.

• Use the 'useradd' command followed by the desired username to add a user.

• You can specify additional options such as the user's home directory and default shell.

• For example, to add a user named 'john' with home directory '/home/john' and default shell '/bin/bash', use: useradd -d /home/john -s /bin/bash john

Expected CTC depends on experience, skills, location, and company size.

• CTC can vary based on the level of experience - junior, mid-level, senior.

• Skills such as expertise in Linux, scripting, networking, and cloud platforms can impact CTC.

• Location plays a role - CTC in metropolitan areas may be higher than in rural areas.

• Company size and industry also influence CTC - tech companies may offer higher salaries.

• Negotiation skills can help in getting a better CTC offer.

SELinux (Security-Enhanced Linux) is a security module for the Linux kernel that provides access control security policies.

• SELinux is a mandatory access control (MAC) system implemented in the Linux kernel.

• It provides fine-grained access control policies, allowing administrators to define rules for how processes and users can interact with files, directories, and other system resources.

• SELinux policies are defined in a set of rules called security contexts, which specify the ...read more

yum is a package manager for Red Hat-based systems, while wget is a command-line tool for downloading files from the internet.

• yum is used for installing, updating, and removing packages on Red Hat-based systems

• wget is used for downloading files from the internet, supports HTTP, HTTPS, and FTP protocols

• yum command example: yum install httpd

• wget command example: wget https://example.com/file.zip

The boot process is the sequence of steps that a computer system goes through to start up and load the operating system.

• BIOS/UEFI initialization

• Boot loader selection and execution

• Kernel initialization

• Init process startup

• User space initialization

Check communications in Linux using tools like ping, traceroute, and netstat to diagnose network issues.

• Use 'ping' to test connectivity to a host: `ping google.com`.

• Use 'traceroute' to see the path packets take to a destination: `traceroute google.com`.

• Use 'netstat' to display network connections and listening ports: `netstat -tuln`.

• Check firewall rules with 'iptables': `iptables -L`.

• Use 'curl' or 'wget' to test HTTP connections: `curl -I http://example.com`.

Linux commands are used to interact with the operating system and perform various tasks.

• Commands are case-sensitive

• Most commands have options and arguments

• Common commands include ls, cd, pwd, mkdir, rm, cp, mv, grep, ps, top, systemctl

• Use man command_name to get more information about a specific command