Essential CentOS, Database, and Networking Interview Topics

Linux CentOS Interview Topics

This section lists core Linux commands grouped by categories such as file and directory operations, file viewing and editing, system information and process management, network-related commands, user and permission management, and other common utilities. Each command includes its function, common options, and usage examples wrapped in

tags.</p>
<ul>
<li><strong>File and Directory Operations</strong>: <code>ls -lh

, cd /etc, pwd, mkdir -p dir1/dir2/dir3, rm -rf file.txt, cp -r file1 file2, mv file1 /dir File Viewing and Editing : cat file.txt , less file.txt , head -n 5 file.txt , tail -f file.log , vi / vim with insert ( i ), exit ( Esc ), save and quit ( :wq ) System Information & Process Management : uname -a , df -h , du -sh /dir , ps aux , top , kill -9 PID , nice -n 10 command , systemctl restart service Network Commands : ip a , ping -c 4 8.8.8.8 , ss -tuln , curl -O http://example.com/file.zip User & Permission Management : whoami , who , su - , useradd username , passwd username , chmod 755 file.txt , chown user:group file.txt Other Common Commands : grep "pattern" file.txt , find / -name "file.txt" , history , man ls Additional interview tips cover bulk file deletion ( rm -f *.log or find /path -type f -name "*.log" -exec rm -f {} \; ), safe use of rm -rf (prefer rm -i ), differences between cp and mv , real‑time log monitoring with tail -f and grep , and advanced less / more usage.

Database Installation & Configuration

The guide outlines MySQL setup on CentOS, including installation via yum , service management with systemctl , and verification commands.

Install MySQL: sudo yum install -y mysql-community-server Start and enable service: sudo systemctl start mysqld and sudo systemctl enable mysqld Check service status: sudo systemctl status mysqld Supplementary interview points discuss checking installation success ( rpm -q mysql-community-server ), viewing service dependencies ( systemctl list-dependencies mysqld ), secure installation ( sudo mysql_secure_installation ), editing /etc/my.cnf for datadir , port , and bind-address , and configuring character sets (utf8mb4) in client, mysql, and mysqld sections. Additional tips include verifying the current character set ( SHOW VARIABLES LIKE 'character_set_server'; ), dynamically changing settings ( SET GLOBAL max_connections = 1000; ), locating data, config, and log directories ( /var/lib/mysql , /etc/my.cnf , /var/log/mysql/ ), and using logrotate for log rotation.

Computer Networking Overview

The networking portion provides a layered breakdown from link layer to application layer, each with core concepts, common protocols, and typical interview questions with concise answers.

Link Layer

Core concepts: framing, physical transmission, error detection (CRC), flow control, MAC addressing.

Key protocols: Ethernet (frame structure), WLAN (IEEE 802.11), PPP.

Sample interview Q&A: Ethernet frame structure, CRC error handling, MAC address purpose, minimum Ethernet frame size (64 bytes), CSMA/CD role.

Network Layer

Core concepts: IP addressing, routing, fragmentation, logical addressing.

Key protocols: IPv4, IPv6, ICMP, ARP.

Sample interview Q&A: IPv4 vs IPv6, subnet mask purpose, viewing routing table ( route -n or ip route), CIDR explanation, NAT purpose.

Transport Layer

Core concepts: reliable (TCP) vs unreliable (UDP) transport, ports, flow and congestion control.

TCP details: three‑way handshake, four‑way termination, sliding‑window protocol, congestion control phases (slow start, avoidance, fast retransmit, fast recovery).

UDP details: connectionless nature, typical use cases (video, voice, DNS), simple data transfer with nc -u -l 1234 and nc -u server_ip 1234.

Interview Q&A cover TCP/UDP differences, handshake steps, sliding‑window purpose, congestion mechanisms, and suitable UDP scenarios.

Application Layer

Core concepts: providing interfaces for applications, common protocols (HTTP, FTP, SMTP, DNS).

HTTP deep dive: statelessness, request/response model, methods, headers, status code categories (1xx‑5xx), and differences between HTTP and HTTPS (TLS encryption, ports 80 vs 443).

Interview Q&A include HTTP vs HTTPS, common status codes, DNS purpose, RESTful API characteristics, and web caching benefits.

Throughout the guide, each protocol or command is accompanied by practical examples and interview‑style questions to help candidates prepare for technical screenings.