Welcome_To_JavaWorld/linux commands at main · polakiganeshkumar/Welcome_To_JavaWorld · GitHub

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1. Basic File System Navigation
How do you list all files in a directory, including hidden ones?
Answer: ls -a

How do you change to the parent directory?
Answer: cd ..

What does pwd do?
Answer: Prints the current working directory.

How do you navigate to the home directory?
Answer: cd ~ or just cd

How do you create an empty file named test.txt?
Answer: touch test.txt

How do you create a directory named projects?
Answer: mkdir projects

How do you recursively copy a directory?
Answer: cp -r source_dir destination_dir

How do you rename a file from old.txt to new.txt?
Answer: mv old.txt new.txt

How do you forcefully delete a directory and its contents?
Answer: rm -rf dir_name

3. File Permissions & Ownership
How do you give the owner execute permission on a script?
Answer: chmod u+x script.sh

How do you change the owner of a file to user1?
Answer: chown user1 file.txt

What does chmod 755 file.sh do?
Answer: Owner gets rwx, group and others get r-x.

How do you change the group of a file to developers?
Answer: chgrp developers file.txt

4. Searching & Finding Files
How do you find all .log files under /var/log?
Answer: find /var/log -name "*.log"

How do you search for "error" in all .txt files?
Answer: grep "error" *.txt

How do you find files modified in the last 7 days?
Answer: find /path -type f -mtime -7

How do you locate the binary path of python?
Answer: which python or whereis python

5. System Monitoring & Processes
How do you list all running processes?
Answer: ps aux or top

How do you kill a process with PID 1234?
Answer: kill 1234 (or kill -9 1234 for force kill)

How do you check disk space usage?
Answer: df -h

How do you check memory usage?
Answer: free -m

How do you check CPU information?
Answer: lscpu or cat /proc/cpuinfo

6. Text Processing
How do you display the first 10 lines of a file?
Answer: head -10 file.txt

How do you display the last 15 lines of a file?
Answer: tail -15 file.txt

How do you count lines, words, and characters in a file?
Answer: wc file.txt

How do you replace "old" with "new" in a file?
Answer: sed 's/old/new/g' file.txt

7. Networking
How do you check open ports?
Answer: netstat -tuln or ss -tuln

How do you ping google.com 5 times?
Answer: ping -c 5 google.com

How do you check the IP address?
Answer: ip a or ifconfig (deprecated)

How do you download a file from the internet?
Answer: wget URL or curl -O URL

8. User & Group Management
How do you add a new user john?
Answer: sudo adduser john

How do you add a user to the sudo group?
Answer: sudo usermod -aG sudo username

How do you list all users?
Answer: cat /etc/passwd or getent passwd

How do you change a user’s password?
Answer: passwd username

9. Compression & Archiving
How do you create a .tar.gz archive?
Answer: tar -czvf archive.tar.gz /path

How do you extract a .tar.gz file?
Answer: tar -xzvf archive.tar.gz

How do you zip a directory?
Answer: zip -r archive.zip /path

10. Advanced Commands
How do you run a command in the background?
Answer: Append & (e.g., sleep 60 &)

How do you check command history?
Answer: history

How do you schedule a job to run daily at 3 AM?
Answer: crontab -e → 0 3 * * * /path/script.sh

Bonus: Scenario-Based Questions
A file is taking too much disk space. How do you find the largest files?
Answer: find / -type f -exec du -h {} + | sort -rh | head -n 10

A service is not starting. How do you check logs?
Answer: journalctl -u service_name or cat /var/log/syslog

How do you check if a remote server is reachable on port 22?
Answer: nc -zv hostname 22 or telnet hostname 22

Final Tips:
Know flags (e.g., -r for recursive, -f for force).

Understand pipes (|) and redirections (>, >>).

Be familiar with Vim (basic editing: i, :wq, :q!).