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Linux File Permissions

·432 words·3 mins·
Linux Security Courses GoogleCybersecurityProgram
Table of Contents

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.