Master Linux Interview Questions: From Boot Process to Advanced Server Commands

Linux Fundamentals

Describe the Linux boot process (BIOS → MBR → bootloader → kernel → init), the meaning of runlevels 0‑6, and the components of a Linux system (kernel, shell, file system, applications). Explain differences between ext2, ext3, and ext4, inode storage, and common commands for killing processes, packaging (tar, gzip, bzip2, zip, rar, etc.), and file system checks (e2fsck).

System Commands and Utilities

Provide examples for counting established connections ( netstat -an | grep ESTABLISHED | wc -l), finding files by modification time, using find with -exec, creating cron jobs, and querying inodes ( ls -i, stat).

Linux Server Topics

Discuss Nginx performance tuning (minimize HTTP, use CDN, enable gzip, set cache headers, reduce redirects, optimize TCP stack). Show Nginx access‑control rules, expiration settings for favicon.ico and robots.txt, custom cache rules, IP‑based access with password protection, and HTTP‑to‑HTTPS redirection.

Explain cookie vs. session mechanisms, load‑balancing strategies (round‑robin, weighted, least connections), making HTTP stateful, TCP reliability versus UDP, CDN principles, DNS resolution flow, CNAME usage, and differences between A and NS records.

Database Fundamentals

Cover MySQL concepts such as SELECT syntax differences, data migration, load‑balancing, transaction properties (ACID), isolation levels, lock types (optimistic vs. pessimistic), common anomalies (dirty read, non‑repeatable read, phantom read), binlog formats (statement, row, mixed), binlog cleanup, replication architecture, and backup/restore techniques (mysqldump with --single-transaction, --master-data, selective table restore).

Shell Script Examples

# Kill a process by name
ps -ef | grep process_name | grep -v grep | awk '{print $2}' | xargs kill -9

# Add 20 users with random passwords
#!/bin/bash
for i in $(seq -f "%02g" 1 20); do
  useradd user$i
  echo "user$i-$(echo $RANDOM | md5sum | cut -c1-5)" | passwd --stdin user$i > /dev/null 2>&1
done

# Check online IPs in 192.168.1.0/24
#!/bin/bash
for ip in $(seq 1 255); do
  ping -c 1 192.168.1.$ip > /dev/null 2>&1 && echo 192.168.1.$ip UP || echo 192.168.1.$ip DOWN
done &

Docker Essentials

Differentiate docker exec (run a new command in a running container) from docker attach (attach to the main process). Explain CMD vs. ENTRYPOINT, and docker stop (graceful SIGTERM then SIGKILL) vs. docker kill (immediate SIGKILL). Provide a volume‑backup example:

docker run --volumes-from AAA -v /tmp:/backup --name BACKUP ubuntu tar cvf /backup/AAA.tar /DATA

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