Understanding File Permissions and Ownership in Linux Print

File permissions and ownership are fundamental parts of Linux security and user management. Understanding how they work helps you control who can read, write, or execute files on your VPS.

This guide will explain how to view and modify file permissions and ownership using simple Linux commands.

1. How to View File Permissions

Use the ls -l command to view detailed file permissions:

ls -l filename

Example output:

-rw-r--r-- 1 root root 4096 Mar 27 12:00 example.txt

Breakdown:

• -rw-r--r-- → File permissions

• 1 → Number of hard links

• root → File owner

• root → File group

• 4096 → File size (in bytes)

• Mar 27 12:00 → Last modified date/time

• example.txt → File name

2. Understanding Permission Flags

The first 10 characters indicate the file type and permissions.

Example: -rwxr-xr--

Permission Types:

• r = read

• w = write

• x = execute

3. Changing File Permissions with chmod

Symbolic Method:

• Add execute permission for owner:

chmod u+x filename

• Remove write permission for group:

chmod g-w filename

• Add read for others:

chmod o+r filename

Numeric (Octal) Method:

Each permission is assigned a value:

• Read = 4

• Write = 2

• Execute = 1

Combine values to set permissions:

chmod 755 filename

This sets:

• Owner: 7 → read (4) + write (2) + execute (1)

• Group: 5 → read (4) + execute (1)

• Others: 5 → read (4) + execute (1)

Common permission sets:

• 755 → typical for scripts or binaries

• 644 → typical for text files (readable by all, writable by owner)

4. Changing Ownership with chown

Change file owner:

chown username filename

Change owner and group:

chown username:groupname filename

Example:

chown john:john example.txt

5. Changing Group Ownership with chgrp

To change only the group:

chgrp groupname filename

6. Recursively Change Permissions or Ownership

To apply changes to a directory and all its contents:

chmod -R 755 /path/to/directory
chown -R user:group /path/to/directory

7. Default Permissions with umask

umask defines default permissions for newly created files and directories.

Check current umask:

umask

Default file permissions are calculated as:

666 - umask value (for files)
777 - umask value (for directories)

Conclusion

Understanding and managing file permissions and ownership is critical for keeping your VPS secure and organized. Always assign the minimum permissions needed for a file or directory to function correctly.

For help with permissions issues or troubleshooting, feel free to contact Hosteons Support.