Sysadmin Linux Theory

chown

Changing file and directory ownership using the chown command for system administration and security management

The chown command changes file and directory ownership in Linux. It’s essential for system administration, security management, and proper file permissions. Only root or the current owner can change ownership.

Key Concepts

  • Owner: User who owns the file/directory
  • Group: Group that owns the file/directory
  • UID/GID: Numeric user and group identifiers
  • Recursive: Apply changes to directories and contents
  • Symbolic Links: How ownership changes affect links

Command Syntax

chown [options] owner[:group] file(s)

  • Changes user ownership, optionally group too
  • Can use usernames or numeric IDs
  • Supports multiple files and wildcards

Common Options

-R - Recursive (include subdirectories) -v - Verbose (show changes made) -c - Show only actual changes --reference=file - Copy ownership from reference file -h - Change symbolic links, not targets

Practical Examples

Example 1: Change user ownership 

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chown alice file.txt
ls -l file.txt
-rw-r--r-- 1 alice users 1024 Dec 15 10:30 file.txt

Changes file owner to user ‘alice’

Example 2: Change user and group 

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chown bob:developers project/
ls -ld project/
drwxr-xr-x 2 bob developers 4096 Dec 15 10:35 project/

Sets owner to ‘bob’ and group to ‘developers’

Example 3: Recursive ownership change 

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chown -R www-data:www-data /var/www/html/

Changes ownership of web directory and all contents

Example 4: Using numeric IDs 

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chown 1001:1001 database.db

Uses numeric user ID 1001 and group ID 1001

Example 5: Copy ownership from reference 

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chown --reference=template.conf new.conf

Copies ownership from existing file

Use Cases

  • Setting up web server file permissions
  • Fixing ownership after file transfers
  • Preparing files for specific applications
  • System administration and user management
  • Securing sensitive files and directories

chgrp - Change group ownership only chmod - Change file permissions ls -l - View current ownership and permissions id - Show user and group IDs stat - Display detailed file information

Tips & Troubleshooting

Permission Issues:

  • Only root can change ownership to different users
  • Regular users can only change group to groups they belong to
  • Use sudo when permission denied

Common Mistakes:

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# Wrong - missing colon for group-only change
chown :group file.txt  # Correct syntax

# Be careful with recursive operations
chown -R user:group /  # NEVER do this!

Security Notes:

  • Verify ownership changes with ls -l
  • Be cautious with recursive operations
  • Don’t change system file ownership unless necessary
  • Use principle of least privilege

Backup Important Files:

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# Before major ownership changes
cp -p original.file backup.file

The -p preserves original ownership and permissions