17 Essential Linux Sysadmin Commands to Boost Productivity

Overview

The following collection presents seventeen frequently used Linux command‑line techniques that address common administrative tasks such as file management, text processing, system monitoring, and security configuration.

1. Move all *.tar files to a backup directory

find . -name "*.tar" -exec mv {} ./backup/ ;

2. Batch unzip all *.zip files to a target directory

for i in `find . -name "*.zip" -type f`; do
  unzip -d $i /data/www/img/
 done

3. Common sed operations (example file: test.txt)

Remove the first character of each line: sed -i 's/^./ /' test.txt Delete the leading dot: sed -i 's/^\.//' test.txt Prepend an a to each line: sed -i 's/^/a/' test.txt Append an a to each line: sed -i 's/$/a/' test.txt Insert c after a matching pattern: sed -i '/wuguangke/a c' test.txt Replace a pattern globally:

sed -i 's:/user/local:/tmp:g' test.txt

4. Test for a directory and create it if missing

if [ ! -d /data/backup/ ]; then
  mkdir -p /data/backup/
else
  echo "The Directory already exists, please exit"
fi

5. Monitor root partition usage and email when ≥90%

# Print usage percentage
df -h | sed -n '/\//p' | awk '{print $5}' | awk -F'%' '{print $1}'
# Loop and send alert
while sleep 5m; do
  for i in `df -h | sed -n '/\//p' | awk '{print $5}' | sed 's/%//g'`; do
    if [ $i -ge 90 ]; then
      echo "More than 90% Linux disk space, please check!" | mail -s "Warn Linux Disk $i%" [email protected]
    fi
  done
done

6. List top 20 IPs from Nginx access log

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

7. Change SELinux mode to disabled

sed -i '/SELINUX/s/enforcing/disabled/' /etc/selinux/config

8. Print maximum and minimum values from a file

# Max value
cat a.txt | sort -nr | awk 'NR==1{print}'
# Min value
cat a.txt | sort -n | awk 'NR==1{print}'
# One‑liner using sed and sort
sed 's/ / /g' a.txt | sort -nr | sed -n '1p;$p'

9. Retrieve SNMP v2c data (example host)

snmpwalk -v2c -c public 192.168.0.241

10. Replace lines ending with jk by yz

sed -e 's/jk$/yz/g' b.txt

11. Basic tcpdump captures

# Capture traffic to 192.168.56.7 on port 80
tcpdump -nn host 192.168.56.7 and port 80
# Exclude host 192.168.0.22 on port 80
tcpdump -nn host 192.168.56.7 or ! host 192.168.0.22 and port 80

12. Show the 20 most frequently used commands

cat .bash_history | grep -v '^#' | awk '{print $1}' | sort | uniq -c | sort -nr | head -20

13. Delete *.log files older than 3 days

find . -mtime +3 -name "*.log" | xargs rm -rf {} ;

14. Move files larger than 100 KB to /tmp

find . -size +100k -exec mv {} /tmp ;

15. Simple firewall allowing only remote access to port 80

iptables -F
iptables -X
iptables -A INPUT -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -p tcp -j REJECT

16. Nginx log analysis – top 10 IPs

cd /home/logs/nginx/default
sort -m -k4 -o access.logok access.1 access.2 access.3 ...
cat access.logok | awk '{print $1}' | sort -n | uniq -c | sort -nr | head -10

17. Replace directory paths in a file

sed -i 's:/user/local:/tmp:g' test.txt

These snippets provide a quick reference for everyday Linux administration, helping engineers automate routine tasks, monitor system health, and enforce basic security policies.