Top Linux Interview Questions: A Guide for Aspiring IT Professionals

Linux: An open-source operating system modeled on UNIX. It’s free to use, modify, and distribute. Known for its stability, security, and flexibility.
Differences: Unlike Windows, Linux offers a variety of distributions catering to different needs. It’s widely used in servers and cloud environments due to its robustness and adaptability.

The Linux file system is arranged in a hierarchical structure. The root (/) is at the top, followed by directories like /bin (essential user binaries), /etc (system configuration files), /home (user directories), /var (variable files), and more.

ls lists directory contents.
cp copies files or directories.
mv moves or renames files or directories.
rm removes files or directories.
mkdir creates a new directory.

chmod Command: File permissions are set using the chmod command, indicating what the owner, group, and others can do with the file (read, write, execute permissions).

Root User: The root is the superuser with full access to the system. It can execute any command and is essential for administrative tasks.

Hard Links: Direct pointers to the data on the disk, sharing the same inode.
Soft Links (Symbolic): Point to other files or directories. They are separate files and have different inodes.

top and htop provide real-time system statistics.
vmstat shows virtual memory statistics.
iostat for CPU and input/output statistics.

ps displays current processes.
top shows real-time process activity.
kill sends signals to terminate processes.
nice changes the priority of a process.

System Logs: Located in /var/log. They record system, application, and security logs. Managed using logrotate.

Boot Process: Involves several stages, including BIOS initialization, MBR loading, GRUB (boot loader) execution, kernel loading, and execution of init scripts.

1. Regular system updates.
2. Configuring firewalls (like iptables).
3. Securing SSH access.
4. Using tools like SELinux for enhanced security.

Uses disk swap space to extend RAM, allowing more processes to run simultaneously.

Process Scheduling: Uses algorithms like Completely Fair Scheduler (CFS) to allocate CPU time to processes.

Distributions: Vary in package management systems (like APT, YUM), desktop environments, and stability vs. cutting-edge software (Ubuntu vs. Fedora, for example).

Scripting: Writing shell scripts (usually Bash) to automate tasks. Scripts can handle file management, system monitoring, and more.

Configuration: Use ifconfig or the ip command to configure network interfaces.

ping to check connectivity.
traceroute to trace the path to a host.
netstat for network statistics.

SSH (Secure Shell): Provides secure remote access to Linux servers.

Use iptables or ufw to manage network traffic rules.

This file maps hostnames to IP addresses. It’s used for local DNS-like resolution, often for testing or managing network devices without a DNS server.

Check for high CPU or memory usage using tools like top or htop. Examine logs for errors. Identify the problematic process/service and investigate further, possibly updating or reconfiguring it.

If a backup isn’t available, tools like testdisk can be used to recover deleted files from the filesystem. It’s important to stop writing to the disk to avoid overwriting the deleted data.

Implement caching mechanisms, use a load balancer, optimize web server settings (Apache/Nginx), and ensure database optimization. Regular monitoring for potential bottlenecks is also essential.

Immediately isolate affected systems. Analyze logs to understand the breach extent. Patch the vulnerability and change all passwords. Restore data from backups if necessary and consider informing affected users.