Here's a complete guide to the chown command in Linux, covering:
What it is
How it works
Syntax
Hands-on examples
Edge cases
20 FAANG-level interview Questions & Answers
🔧 What is chown?
The chown (change owner) command changes the ownership of a file, directory, or symbolic link.
It can change:
User ownership
Group ownership
Or both at the same time.
🧠 Syntax
chown [OPTIONS] USER[:GROUP] FILE...
Examples:
chown prakash file.txt → change owner to prakash
chown prakash:admin file.txt → change owner to prakash, group to admin
chown :admin file.txt → change group only
🧪 Practical Hands-On Examples
1. Change ownership of a file
chown prakash report.txt
Sets the user owner of report.txt to prakash.
2. Change user and group
chown prakash:devops script.sh
Changes the file script.sh to be owned by user prakash and group devops.
3. Change group only
chown :devops log.txt
4. Change ownership recursively
chown -R prakash:devops /home/prakash/project/
Changes ownership for all files and directories inside /home/prakash/project.
5. Use --from to change owner only if current owner matches
chown --from=root prakash file.txt
Changes owner only if the current owner is root.
6. Symbolic link behavior
chown prakash symlink
Changes the ownership of the target file, not the link.
To change the link itself:
chown -h prakash symlink
7. Change ownership using UID and GID
chown 1001:1002 file.txt
⚠️ Edge Cases and Pitfalls
🔍 Ownership Check Before and After
ls -l file.txt
🔐 Permissions Required
Only root or a user with CAP_CHOWN capability can:
Change file ownership
Change to another user
🧠 20 FAANG-Level Questions & Answers on chown
🔸 Q1. What’s the difference between chown and chmod?
A:
chown: Changes owner and group
chmod: Changes file permission bits (read/write/execute)
🔸 Q2. How do you change only the group of a file?
chown :groupname file
🔸 Q3. Can a non-root user change ownership of their own file to another user?
A: No, only root can change ownership to another user.
🔸 Q4. How to recursively change ownership of a directory and its contents?
chown -R user:group /path/
🔸 Q5. What happens when you run chown -h symlink?
A:
Changes the ownership of the symbolic link itself, not the target.
🔸 Q6. How can chown --from help in scripts?
A:
Ensures you only change ownership if the current owner matches, avoiding accidental overwrites.
🔸 Q7. How can you prevent chown from following symlinks recursively?
chown -hR user:group directory
🔸 Q8. What happens if chown is run on a mounted NFS filesystem?
A:
May fail depending on NFS server settings.
root_squash may map root to nobody.
🔸 Q9. How can find and chown be used together to change specific files?
find . -type f -name "*.log" -exec chown prakash:logs {} \;
🔸 Q10. Can you use chown with wildcards?
chown prakash:devops *.sh
✅ Yes, if the shell expands the pattern before passing it to chown.
🔸 Q11. How to log what chown is changing?
chown -v prakash file.txt
🔸 Q12. Why might chown silently fail in a Docker container?
A:
You may lack capabilities
Files are owned by read-only volume
UID/GID mismatch in base image
🔸 Q13. Can chown be used to remove group ownership?
A:
No. But you can set to a neutral group or use chmod to restrict group access.
🔸 Q14. How to debug chown failures on immutable files?
lsattr file.txt
chattr -i file.txt
chown prakash file.txt
🔸 Q15. Explain a real-world CI/CD scenario for using chown
A:
When building Docker containers, changing ownership of /app can prevent permission issues for apps running under a non-root user.
🔸 Q16. How does chown affect ACLs (Access Control Lists)?
A:
It changes the owning user but does not affect extended ACLs unless explicitly modified.
🔸 Q17. How do you use chown to match UID/GID of a remote system?
chown 501:1000 file.txt
🔸 Q18. Why use sudo chown in automation scripts?
A:
Ensure ownership is correct for system processes (like nginx writing to /var/www), and prevent permission denied issues.
🔸 Q19. Can you use chown inside a GitHub Action or Jenkins pipeline?
A:
Yes, to ensure build artifacts are owned by the runner user.
🔸 Q20. What’s the security risk of misusing chown?
A:
Changing ownership to a less privileged user might leak sensitive files, or allow malicious users to tamper with system binaries.
✅ Summary
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