Essential Linux Commands Every Ops Engineer Needs (2W+ Salary Guide)

2W+ Salary Ops Engineer Linux Command List (Save for Reference)

As an operations engineer, mastering Linux commands is fundamental. Whether for daily maintenance or interview assessments, these commands are indispensable. This article systematically organizes essential Linux commands from a practical perspective, illustrating usage with real-world scenarios.

1. File and Directory Operations: The Basics

1.1 File Viewing Commands

# View file content
cat /etc/passwd
# Show full file content
more /var/log/messages
# Paginated view of large files
less /var/log/syslog
# Flexible pagination
head -20 /var/log/nginx.log
# Real‑time log monitoring
tail -f /var/log/apache.log

Interview question: What is the difference between more and less? more can only scroll forward, while less can scroll both forward and backward. less uses less memory, suitable for large files. less supports searching (e.g., /keyword).

1.2 File Search Commands

# Advanced find usage
find /var/log -name "*.log" -mtime -7   # logs modified in last 7 days
find /home -type f -size +100M          # files larger than 100 M
find /etc -name "*.conf" -exec grep -l "port" {} \;  # config files containing "port"

# locate (requires updatedb)
updatedb
locate nginx.conf

# which and whereis
which python3
whereis nginx

1.3 File Permission Management

# View and modify permissions
ls -la /etc/passwd
chmod 755 /usr/local/bin/script.sh
chmod u+x,g+r,o-w filename
chown nginx:nginx /var/www/html
chgrp www-data /var/log/nginx/

# Special permissions
chmod +t /tmp      # sticky bit
chmod +s /usr/bin/passwd   # SUID

2. System Monitoring and Performance Analysis

2.1 System Resource Monitoring

# CPU and memory
 top
 htop
 ps aux | grep nginx
 ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head -10

# Memory analysis
 free -h
 cat /proc/meminfo
 vmstat 1 5

2.2 Disk Space Management

# Disk usage
 df -h
 du -sh /var/log/*

# Find largest files/directories
 du -ah /home | sort -rh | head -20

# Disk I/O monitoring
 iostat -x 1
 iotop

2.3 Network Monitoring

# Connection status
 netstat -tulpn
 ss -tulpn
 lsof -i :80

# Traffic monitoring
 iftop
 nethogs
 tcpdump -i eth0 port 80

3. Text Processing and Log Analysis

3.1 Text Processing Trio

# grep examples
grep -r "error" /var/log/
grep -i "failed" /var/log/auth.log
grep -v "INFO" /var/log/app.log | head -20
grep -E "192\.168\.1\.[0-9]+" access.log

# sed examples
sed 's/old/new/g' file.txt
sed -n '10,20p' file.txt
sed -i 's/DEBUG/INFO/g' config.conf
sed '/^#/d' config.conf

# awk examples
awk '{print $1}' /var/log/nginx/access.log
awk -F: '{print $1}' /etc/passwd
awk '$3 > 100 {print $0}' data.txt

3.2 Log Analysis Practice

# Top IPs
awk '{print $1}' access.log | sort | uniq -c | sort -nr | head -10

# Count 404 errors
awk '$9 == 404 {print $0}' access.log | wc -l

# Time distribution
awk '{print $4}' access.log | cut -d: -f2 | sort | uniq -c

# Status code counts
awk '{print $9}' access.log | sort | uniq -c | sort -nr

4. Process Management and Service Control

4.1 Process Management

# Kill processes
kill -9 PID
killall nginx
pkill -f "python script"
pgrep -f nginx

# Background jobs
nohup command &
jobs
bg %1
fg %1

4.2 System Service Management

# systemd
systemctl start nginx
systemctl stop nginx
systemctl restart nginx
systemctl reload nginx
systemctl enable nginx
systemctl disable nginx
systemctl status nginx

# View logs
journalctl -u nginx
journalctl -f -u nginx

5. Network Configuration and Troubleshooting

5.1 Network Configuration

# IP configuration
ip addr show
ip route show
ip link show

# Traditional commands
ifconfig eth0
route -n
arp -a

5.2 Network Troubleshooting

# Connectivity tests
ping -c 4 google.com
traceroute google.com
mtr google.com

# Port tests
telnet 192.168.1.1 80
nc -zv 192.168.1.1 80

6. Compression and Backup

6.1 File Compression

# tar
 tar -czf backup.tar.gz /var/www/
 tar -xzf backup.tar.gz
 tar -tzf backup.tar.gz
 tar -czf backup-$(date +%Y%m%d).tar.gz /etc/

# zip
 zip -r backup.zip /var/www/
 unzip backup.zip
 gzip file.txt
 gunzip file.txt.gz

6.2 Data Synchronization

# rsync
 rsync -avz /var/www/ user@remote:/backup/
 rsync -avz --delete /var/www/ /backup/
 rsync -avz --exclude='*.log' /var/www/ /backup/

7. System Security and User Management

7.1 User Management

# User operations
useradd -m -s /bin/bash username
usermod -aG sudo username
passwd username
userdel -r username

# View user info
id username
who
w
last

7.2 System Security

# Log inspection
 tail -f /var/log/auth.log
 grep "Failed password" /var/log/auth.log
 grep "sudo" /var/log/auth.log

# File integrity
 md5sum file.txt
 sha256sum file.txt

8. Advanced Command Techniques

8.1 Command Pipelines

# Complex pipeline example
ps aux | grep nginx | grep -v grep | awk '{print $2}' | xargs kill -9

# Top requesting IPs
cat /var/log/nginx/access.log | grep "GET" | awk '{print $1}' | sort | uniq -c | sort -nr | head -10

# Find logs containing "error"
find /var/log -name "*.log" -exec grep -l "error" {} \; | xargs ls -la

8.2 Scripting for Ops

# One‑click system info script
#!/bin/bash
echo "=== System Info ===" > system_info.txt
uname -a >> system_info.txt
echo "=== CPU Info ===" >> system_info.txt
cat /proc/cpuinfo | grep "model name" | head -1 >> system_info.txt
echo "=== Memory Info ===" >> system_info.txt
free -h >> system_info.txt
echo "=== Disk Info ===" >> system_info.txt
df -h >> system_info.txt
echo "=== Network Info ===" >> system_info.txt
ip addr show >> system_info.txt

9. Common Interview Questions

9.1 Performance Tuning

Q: How to view system load?

uptime
cat /proc/loadavg
w

Q: How to troubleshoot high CPU usage?

top -p PID
strace -p PID
perf top

9.2 Storage Management

Q: How to find the largest files?

du -ah /var | sort -rh | head -20
find /var -type f -size +100M -exec ls -lh {} \;

Q: How to monitor filesystem usage?

df -h
inotifywait -m /var/log/

10. Practical Scenario Exercises

10.1 Server Fault‑Diagnosis Workflow

# Basic checks
uptime && free -h && df -h

# Process check
ps aux | head -20
top -n 1 | head -20

# Network check
netstat -tulpn | grep LISTEN
ss -tulpn

# Log check
tail -50 /var/log/messages
journalctl -xe

10.2 Daily Maintenance Script

#!/bin/bash
LOG_FILE="/var/log/health_check.log"
DATE=$(date '+%Y-%m-%d %H:%M:%S')
echo "[$DATE] Starting system health check" >> $LOG_FILE

# Disk usage warning
DISK_USAGE=$(df -h | grep -E "8[0-9]%|9[0-9]%|100%")
if [ -n "$DISK_USAGE" ]; then
  echo "[$DATE] Warning: High disk usage" >> $LOG_FILE
  echo "$DISK_USAGE" >> $LOG_FILE
fi

# Memory usage warning
MEM_USAGE=$(free | grep Mem | awk '{print ($3/$2) * 100.0}')
if (( $(echo "$MEM_USAGE > 90" | bc -l) )); then
  echo "[$DATE] Warning: High memory usage: $MEM_USAGE%" >> $LOG_FILE
fi

# Load average warning
LOAD_AVG=$(uptime | awk -F'load average:' '{print $2}' | cut -d, -f1 | tr -d ' ')
if (( $(echo "$LOAD_AVG > 2.0" | bc -l) )); then
  echo "[$DATE] Warning: High load average: $LOAD_AVG" >> $LOG_FILE
fi

echo "[$DATE] System health check completed" >> $LOG_FILE

Conclusion

Mastering these Linux commands will not only help you stand out in interviews but also boost efficiency in real‑world operations, enabling rapid problem identification and resolution. Remember, commands are tools; true expertise lies in understanding system principles and applying them flexibly.

As an operations engineer, you should:

Practice hands‑on in test environments.

Understand the underlying mechanisms of each command.

Combine commands to improve workflow.

Prioritize system security and adopt good operational habits.

Continuously learn new tools and technologies.