45 Essential Linux Commands Every Sysadmin Should Master

Compiled in a "command combo + real‑world scenario" format, this cheat sheet lists the 45 most commonly used and efficient Linux commands for daily operations, covering file manipulation, search and cleanup, system monitoring, network troubleshooting, log analysis, text processing, and disk cleanup, which together address about 99% of typical sysadmin needs.

1. Batch File Operations

Batch create files: touch haodao{1..100}.py Generate large files quickly: dd if=/dev/zero of=test.txt bs=1M count=1024 Five ways to empty a file: > file, truncate -s 0 file, cat /dev/null > file, etc.

2. Advanced find Search and Cleanup

Search by name, type, permissions, size, or time: find . -name "*.py" (by suffix) find . -type f -perm 777 (by permission) find . -size +100M -size -1G (by size range) find . -mtime +7 -name "*.py" | xargs rm -rf (by time + name for cleanup)

3. System Resource Monitoring

View CPU model and core count: cat /proc/cpuinfo | grep name | uniq -c Top 20 processes by memory usage: ps aux | sort -rnk 4 | head -20 Top 20 processes by CPU usage: ps aux | sort -rnk 3 | head -20 Run commands in background:

nohup cmd > /dev/null 2>&1 &

4. Log and Access Analysis

Tomcat log analysis examples

Count unique IPs in a time window: awk '{print $4,$1}' access.log | grep "11/Dec/2022:09" Top 20 visiting IPs:

awk '{print $1}' access.log | sort | uniq -c | sort -nr | head -20

Pages visited by a specific IP:

grep ^IP access.log | awk '{print $7}'

5. Text Processing with sed

Replace a string: sed -i 's/haodao/HAODAO/g' file.py Replace a path: sed -i 's:/etc/dhcp:/home:g' file.py Various tricks: add content at line start/end, delete comments, insert before/after specific lines, etc.

6. Network Capture and Port Analysis

Precise packet capture with tcpdump:

Capture a specific port: tcpdump -i ens33 port 8080 -n Capture a range of ports: tcpdump portrange 80-443 -i ens33 -n Capture ICMP from a source IP: tcpdump icmp and src 192.168.20.231 -i ens33 -n Top IPs connecting to a port:

netstat -anlp | grep 80 | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c | sort -nr | head -15

7. Disk and Directory Cleanup

Identify large files in /var: du -xBM --max-depth=2 /var | sort -rn | head -20 Top 10 large files in current directory:

du -s * | sort -n | tail

One‑Sentence Summary

These 45 command combos form a full‑stack operations toolbox—covering file handling, system monitoring, log analysis, network troubleshooting, text processing, and disk cleanup—that can solve roughly 99% of everyday Linux sysadmin scenarios, and are worth bookmarking and mastering.