Essential Linux Command Cheat Sheet for Ops and Developers

1. Files and Directories

ls -lah

– List directory contents with detailed info; use --time-style=long-iso for standardized timestamps. cd - – Return to the previous directory. pwd – Show the current working directory (useful for script location). cp -rv source dest – Copy files/directories recursively while showing progress. mv source dest – Move or rename files; mv file /tmp can act as a quick delete. rm -rf path – Force delete (use with caution; consider trash as a safer alternative). find -name "*.log" – Search for files; combine with -exec rm for batch deletion.

2. Text Viewing and Processing

cat a.txt b.txt > c.txt

– Concatenate and view files. less file – Paginated view with search (e.g., /error). head -n 50 log.txt – Show the first N lines. tail -f /var/log/syslog – Follow the last N lines in real time. grep -ri error /var/log – Recursively search for a keyword. awk '{print $1,$3}' log.txt – Extract specific columns. sed -i 's/old/new/g' file – In‑place text replacement. jq '.key' config.json – Parse JSON data.

3. System Management

ps aux

– List all running processes. kill -9 1234 – Force‑terminate a process by PID. top / htop – Real‑time system resource monitoring (htop offers a more intuitive UI). df -h – Show disk usage; combine with ncdu for detailed analysis. du -sh /var/* – Display directory size summaries. free -h – Display memory usage and check for OOM conditions. uptime – Show system uptime and load average (load > 1 may need investigation). iostat -dx 2 – Monitor disk I/O (requires sysstat package).

4. Networking and Connectivity

ping 8.8.8.8

– Test network reachability. curl -I https://example.com – Perform HTTP request testing. wget https://file.com/app.tar.gz – Download files. ss -lntp – List listening TCP ports. scp file user@host:/path – Securely copy files to a remote host. ssh user@host – Open a remote shell session. telnet host 80 – Test TCP port connectivity.

5. Compression and Archiving

tar -czvf file.tar.gz dir/

– Create a gzipped tar archive. tar -xzvf file.tar.gz – Extract a gzipped tar archive. zip -r file.zip dir/ – Create a zip archive. unzip file.zip – Extract a zip archive. tar --exclude='*.log' -czvf backup.tar.gz data – Archive while excluding log files.

6. Permissions and User Management

chmod 755 file

– Change file permissions. chown user:group file – Change file ownership. sudo command – Execute a command with elevated privileges. su - user – Switch to another user account. useradd -m user – Create a new user with a home directory. passwd user – Change a user's password.

7. Software Management

Debian/Ubuntu: apt install pkg / apt remove pkg CentOS/RHEL: yum install pkg / yum remove pkg Generic RPM: rpm -ivh pkg.rpm /

rpm -e pkg

8. Command Composition and Redirection

# Real‑time log + keyword filter
 tail -f /var/log/syslog | grep --color=always error

# Write both stdout and stderr to a file
 command > out.log 2>&1

# Delete log files older than 30 days
 find /var/log -name "*.log" -type f -mtime +30 -exec rm -f {} \;

9. Lesser‑Known but Powerful Tools

ncdu – Interactive disk usage analyzer.

bat – Cat with syntax highlighting.

ag – Ultra‑fast code/text search.

tmux – Terminal multiplexer for multiple sessions.

htop – Enhanced version of top.

10. Everyday Troubleshooting Quick‑Reference

Permission denied – Fix with sudo chmod 755 file and chown as needed.

Garbage characters (Chinese garbled) – Set locale: export LANG="en_US.UTF-8".

Accidental file deletion – Recover using extundelete (unmount the partition first).

Port already in use – Identify with ss -lntp.