Linux, Security & Troubleshooting

What is Linux?

An open-source operating system commonly used for servers, cloud environments, and enterprise infrastructure.

Why is Linux commonly used on servers?

It is stable, secure, efficient, and highly customizable.

What does ls do?

Lists files and directories in the current directory.

What does pwd do?

Displays the current working directory.

What does cd do?

Changes the current working directory.

What does mkdir do?

Creates a new directory.

What does rm do?

Deletes files or directories.

What does cp do?

Copies files or directories.

What does mv do?

Moves or renames files and directories.

What does cat do?

Displays the contents of a file.

What does grep do?

Searches files or text for a specified word or pattern.

What does chmod do?

Changes file or directory permissions.

What does ps do?

Displays currently running processes.

What does top do?

Displays real-time system resource usage and running processes.

What does kill do?

Terminates a running process.

What is a process?

A running instance of a program.

What is a service?

A background program that performs system tasks and supports applications.

What are file permissions?

Rules that determine who can read, write, or execute a file.

What is encryption?

The process of converting readable data into unreadable data using an algorithm and key.

Why is encryption important?

It protects sensitive information from unauthorized access.

What is hashing?

A one-way process that converts data into a fixed-length value used for verification.

What is logging?

Recording system or application events for monitoring and troubleshooting.

Why are logs important?

They help identify errors, debug issues, monitor activity, and investigate security incidents.

What is debugging?

The process of finding, analyzing, and fixing software defects.

What is troubleshooting?

A systematic process for identifying and resolving technical problems.

What is the first step in troubleshooting?

Understand and clearly identify the problem before attempting a solution.

What should you check if an application suddenly stops working?

Check logs, verify configuration, inspect error messages, test network connectivity, and verify dependent services are running.

What is a dependency?

A software component or service that another application relies on to function.

What is monitoring?

Continuously observing the health and performance of systems and applications.

What is uptime?

The amount of time a system remains operational without interruption.

What is downtime?

The period when a system or application is unavailable.

How would you troubleshoot a slow application?

Check CPU and memory usage, review logs, verify database performance, inspect network latency, and identify recent configuration changes.

How would you troubleshoot a service that won't start?

Check the service status, review logs, verify configuration files, confirm dependencies are running, and restart the service after resolving any issues.

How would you troubleshoot a database connection failure?

Verify the database server is running, confirm the connection string and credentials, check firewall and network connectivity, and review application logs for errors.

How do logs help during troubleshooting?

They provide timestamps, error messages, and execution details that help identify the root cause of a problem.