100+ Linux System Administrator Interview Questions and Answers

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

The command used to check memory status is 'free'.

• The 'free' command displays the total amount of free and used physical and swap memory in the system.

• It also shows the buffers and cache used by the kernel.

• The output of the 'free' command can be customized using various options like '-h' for human-readable format and '-s' for a continuous display.

• Another command that can be used to check memory status is 'top', which displays the memory usage of individual processes in real-t...read more

The question is about Linux System Administration and covers various topics such as Apache virtualization, Tomcat installation and configuration, AWS EC2 and S3 bucket, VMware management, database migration, LVM configuration and management, SSL configuration, ISCSI server and client configuration, haproxy configuration and management, and database replication.

• Apache virtualization

• Tomcat installation and configuration

• AWS EC2 and S3 bucket

• VMware management

• Database migration (M...read more

The maximum size of a filename in Linux is 255 bytes.

• The maximum length includes the entire path and filename.

• The limit is imposed by the file system, not the operating system.

• Some file systems, such as ext4, support longer filenames with special configuration.

• Long filenames can cause issues with some applications and scripts.

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

SSH port number is 22 by default. RPM is a package manager for Red Hat-based systems, while YUM is a higher-level package manager that uses RPM as its backend. To remove a text file in Linux, you can use the 'rm' command. Chmod is a command used to change the permissions of a file or directory.

• SSH port number is typically 22, but it can be changed in the SSH server configuration file.

• RPM is a low-level package manager used for installing, upgrading, and removing software pack...read more

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

To configure Apache server in Red Hat 7.9, follow these steps:

• Install Apache using yum package manager

• Start Apache service and enable it to start at boot

• Configure firewall to allow HTTP traffic

• Create virtual hosts for multiple websites

• Configure SSL/TLS encryption for secure connections

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

To create a blank file in RHEL, you can use the 'touch' command.

• Open the terminal in RHEL.

• Use the 'touch' command followed by the desired file name to create a blank file.

• For example, to create a file named 'example.txt', you would run: touch example.txt

• The 'touch' command can also be used to update the timestamp of an existing file.

lsblk command is used to list block devices in RHEL.

• Displays information about all available or the specified block devices.

• Shows the device name, size, mount point, and file system type.

• Can be used to identify unmounted disks or partitions.

• Can also be used to check the status of a disk or partition.

• Example: lsblk -a -o NAME,SIZE,MOUNTPOINT,FSTYPE

LVM (Logical Volume Manager) is configured by creating physical volumes, volume groups, and logical volumes.

• Create physical volumes using the 'pvcreate' command

• Create volume groups using the 'vgcreate' command

• Create logical volumes using the 'lvcreate' command

• Format the logical volumes with a file system using the 'mkfs' command

• Mount the logical volumes to desired mount points using the 'mount' command

• Update the '/etc/fstab' file to mount the logical volumes at boot

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

The pink command is not a valid Linux command.

• There is no pink command in Linux.

• It is possible that the interviewer is testing the candidate's honesty and ability to admit when they don't know something.

• The candidate should respond honestly and explain that they are not familiar with the pink command.

• Alternatively, the candidate could ask for clarification or context to better understand the question.

To kill a process in RHEL 7.2, use the 'kill' command followed by the process ID.

• Identify the process ID using 'ps' command

• Use 'kill' command followed by the process ID to terminate the process

• Use 'kill -9' command to force kill the process if it doesn't respond to regular kill command

Patching physical servers involves identifying vulnerabilities, testing patches, scheduling downtime, and applying patches.

• Identify vulnerabilities through vulnerability scanning or manual review

• Test patches in a non-production environment to ensure compatibility and stability

• Schedule downtime with stakeholders and communicate the impact of the patching

• Apply patches using a patch management tool or manually

• Verify the success of the patching and monitor for any issues post-pat...read more

To migrate a SUSE enterprise server from SLES 12 SP2 to SLES 15 SP2, you can use the online migration method.

• Ensure that the server meets the minimum requirements for SLES 15 SP2

• Backup all important data before starting the migration process

• Use the 'zypper' package manager to perform the online migration

• Follow the official SUSE documentation for detailed steps and best practices

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

To take a snapshot of a machine, you can use the built-in tools provided by the virtualization platform or third-party software.

• Use the snapshot feature provided by the virtualization platform such as VMware vSphere or Hyper-V.

• For Linux machines, you can use tools like LVM (Logical Volume Manager) to create snapshots of the filesystem.

• Third-party backup and snapshot tools like Veeam or Acronis can also be used for taking snapshots.

• Ensure that the machine is in a stable state ...read more

Netstat is a command-line tool used to display network connections, routing tables, and network interface statistics.

• Displays active network connections and their status

• Shows routing tables and network interface statistics

• Can be used to troubleshoot network issues

• Can be used to identify open ports and listening services

• Syntax: netstat [options]

FSMO stands for Flexible Single Master Operations. It is a role in Active Directory that controls specific domain-wide operations.

• FSMO roles are divided into two categories: forest-wide and domain-wide.

• There are five FSMO roles: Schema Master, Domain Naming Master, RID Master, PDC Emulator, and Infrastructure Master.

• The Schema Master controls all updates and modifications to the schema.

• The Domain Naming Master controls the addition or removal of domains in the forest.

• The RID ...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.

Cron tab is a time-based job scheduler in Linux used to automate repetitive tasks. It runs in the background and executes commands at specified intervals.

• Cron tab is configured using the 'crontab' command

• Each user has their own crontab file located in /var/spool/cron/crontabs/

• The syntax for setting up a cron job is: * * * * * command-to-be-executed

• The five asterisks represent the minute, hour, day of the month, month, and day of the week respectively

• Examples: 0 0 * * * /path/...read more

Patching is the process of applying updates or fixes to software or systems to address vulnerabilities or improve functionality.

• Patching involves downloading and installing updates provided by software vendors.

• It helps to fix bugs, security vulnerabilities, and improve performance.

• Patches can be applied to operating systems, applications, or firmware.

• Regular patching is crucial to maintain system integrity and protect against cyber threats.

• Examples include applying security p...read more