Advanced Linux Commands for the Modern Hacker
Linux, the backbone of most modern servers and a favorite amongst the hacker community, offers a robust collection of commands that grant unparalleled access to a computer’s inner workings. Whether you’re a penetration tester, ethical hacker, or just a Linux enthusiast, understanding advanced commands is essential to mastering Linux and its potential.
Disclaimer:The information provided here is meant for educational purposes only. Unauthorized hacking is illegal, and understanding these tools doesn’t grant license to misuse them.
1. Netcat (`nc`)
Overview: Netcat is a versatile networking utility. It can read from and write to TCP and UDP sockets, making it an essential tool for network debugging and exploration.
Use Cases: Creating chat systems, port scanning, banner grabbing, backdoors, file transfers.
Examples:
Simple Chat System:
1. Host: `nc -lvp 8080`
2. Client: `nc [host_ip] 8080`
File Transfer:
1. Receiver: `nc -lvp 8080 > received_file.txt`
2. Sender: `nc [receiver_ip] 8080 < send_file.txt`
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2. Tcpdump
Overview: Tcpdump captures packets that traverse a network interface. It’s invaluable for network troubleshooting and understanding traffic patterns.
Use Cases: Traffic analysis, malicious activity detection, debugging.
Examples:
Capture first 10 packets on eth0:
`tcpdump -i eth0 -c 10`Capture HTTP requests:
`tcpdump -i eth0 ‘port 80’`
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3. Nmap
Overview: A powerful network scanning tool, Nmap can discover devices running on a network and find open ports along with various attributes of the network.
Use Cases: Network inventory, maintenance, vulnerability detection.
Examples:
OS Detection:
`nmap -O [target_ip]`Aggressive Scan:
`nmap -A [target_ip]`
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4. Chroot
Overview: Chroot changes the apparent root directory for the current process and its children.
Use Cases: Creating an isolated environment for software compilation, testing, or service segregation.
Examples:
Isolate a Service:
1. `mkdir /srv/newroot`
2. `chroot /srv/newroot /usr/bin/someservice`
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5. Strace
Overview: Strace intercepts and logs system calls made and signals received by a process.
Use Cases: Debugging, performance profiling, error tracking.
Examples:
Track File Access:
`strace -e trace=file [command]`
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6. Lsof
Overview: Lsof lists open files, revealing the file descriptors used by a process.
Use Cases: Detecting rogue processes, security audits, system investigation.
Examples:
Find Processes Using a Directory:
`lsof +D /path/to/directory`
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7. Iptables
Overview:The user-space utility to configure the IP packet filter rules of the Linux kernel.
Use Cases:Building firewalls, IP masquerading, network translation.
Examples:
Allow Traffic on Port 80:
`iptables -A INPUT -p tcp — dport 80 -j ACCEPT`
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8. Grep
Overview: Grep searches input files for a pattern.
Use Cases: Data retrieval, log analysis, scripting.
Examples:
Find Errors in a Log File:
`grep “ERROR” /var/log/syslog`
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9. Sed & Awk
Overview: Sed and Awk are stream editors for filtering and transforming text.
Use Cases:Text processing, data extraction, report generation.
Examples:
Replace ‘old’ with ‘new’ in a File using Sed:
`sed ‘s/old/new/g’ filename`Print the Second Column of a CSV using Awk:
`awk -F, ‘{print $2}’ filename.csv`
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10. Find
Overview: Find searches for files in a directory hierarchy.
Use Cases: System cleanup, data location, permission checks.
Examples:
Find Files Larger Than 100MB:
`find / -type f -size +100M`
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Extra : Cron
Overview: Cron is a time-based job scheduler.
Use Cases: Automating scripts, backups, notifications.
Examples:
Run a Script Every Day at 3 AM:
Add to crontab: `0 3 * * * /path/to/script.sh`
Conclusion:
These commands form the bedrock of Linux system management and networking. Mastery requires not just reading but hands-on practice. Use them wisely and always ensure you have permissions, especially when working on live environments or networks. The Linux command line is a world of endless possibilities, so never stop exploring!
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