Linux File Permissions

Project Description

This project demonstrates practical Linux administration skills by using core commands like ls and chmod to manage and understand POSIX permissions.

Step 1: Checking File and Directory Permissions

To check existing file permissions of the projects directory:

ls -la /home/user91/projects/

Sample output:

drwxr-xr-x 4 user91 researchers 4096 Feb 2 14:30 .
drwxr-xr-x 3 root        root        4096 Feb 10 14:30 ..
-rw-rw-r-- 1 user91 researchers 1024 Feb 2 14:30 project_a.md
-rw-r--r-- 1 user91 researchers 2048 Feb 2 14:30 .project_x.txt
drwxrwxr-x 2 user91 researchers 4096 Feb 2 14:30 drafts

Understanding the 10-Character Permission Strings

10-character string representation: drw-rw-r-x

1. First character: File type (- = regular file, d = directory)
2. Characters 2-4 (next 3): User permissions (read, write, execute).
3. Characters 5-7 (next 3): Group permissions (read, write, execute).
4. Characters 8-10 (last 3): Others permissions (read, write, execute)

Example: -rw-r--r--

• - indicates a regular file.
• rw- means the user can read and write.
• r-- means the group can only read.
• r-- means others can only read.

Step 2: Modifying File Permissions Using chmod

A. Removing Unauthorized Write Access

Problem: project_a.md has unsafe permission rw-rw-rw- (Group and others have write access to the file).

Solution:

chmod 644 /home/user91/project_a.md

This command sets the permissions to:

• User: Read and write (6 = 4 + 2)
• Group: Read only (4)
• Others: Read only (4)

After running the command, the file’s permissions were confirmed with:

ls -la /home/user91/project_a.md

Result:

-rw-r--r-- 1 user91 researchers 1024 Feb 2 14:30 project_a.md

B. Adjusting Permissions for a Hidden File

Problem: The research team archived the hidden file .project_x.txt. It should have no write permissions, with read permissions granted to the user and group. I used the following command:

Solution:

chmod u=r,g=r,o= /home/user91/.project_x.txt

This command updates the permissions as follows:

• Owner: Read only (4)
• Group: Read only (4)
• Others: No permissions (0)

Verify Permissions:

ls -la /home/user91/.project_x.txt

Result:

-r--r----- 1 user91 researchers 2048 Feb 2 14:30 .project_x.txt

C. Restricting Directory Access

Requirement: Only the user user91 should access the drafts directory.

Solution:

chmod 700 drafts/

This command ensures that:

• User (user91): Full access (read, write, execute)
• Group & Others: No access

Verifying the change:

ls -la /path/to/drafts

Result:

drwx------ 2 user91 researchers 4096 Feb 2 14:30 drafts

Summary

This project showcased the practical application of Linux commands to manage file permissions securely.

Which included:

1. Permission auditing using ls -la
2. Removing group write access from project files
3. Securing archived documents with proper hidden file permissions
4. Implementing strict directory access controls

This exercise not only reinforced my command-line skills but also highlighted the importance of proper authorization and principle of least privilege in maintaining system security.