🔐 Secure Shared Logging: Creating a Centralized Logs Directory for Multiple Linux Users

🎯 Objective

In multi-user Linux environments, there are often requirements where several users must be able to submit logs or reports in a shared location — without having the ability to modify or delete each other’s files. This project demonstrates how to configure such a secure, centralized directory called /central_logs.

🔍 Project Overview

We aim to:

• Create a shared directory /central_logs
• Allow all users to write (add) their own files
• Prevent users from modifying or deleting each other’s files
• Let all users list the contents of the directory

To simulate this, we will create two test users: user1 and user2.

⚙️ Step-by-Step Implementation

1️⃣ Create the Central Directory

sudo mkdir /central_logs

2️⃣ Create Test Users

sudo useradd user1
sudo useradd user2
# Set passwords
sudo passwd user1
sudo passwd user2

✅ Note: If the users already exist, skip this step.

3️⃣ Set Group Ownership and Permissions

We’ll use the Sticky Bit concept — commonly used in directories like /tmp.

sudo chmod 1777 /central_logs

🔍 What does 1777 mean?

• 1 – Sticky Bit: Only the file's owner or root can delete or rename their own files.
• 7 – Read, write, execute for owner
• 7 – Read, write, execute for group
• 7 – Read, write, execute for others

This allows:

• All users to write to the directory
• Only the owner of a file to modify or delete it

🧪 Testing and Verification

✅ Switch to user1 and Create a File

su - user1
echo "Log file from user1" > /central_logs/user1_log.txt

✅ Switch to user2 and Try to Delete user1's File

su - user2
rm /central_logs/user1_log.txt

Output:

rm: cannot remove '/central_logs/user1_log.txt': Operation not permitted

🎉 Success! user2 cannot delete user1's file.

✅ Now, Let user2 Create Their Own File

echo "Log file from user2" > /central_logs/user2_log.txt

✅ Both Users Can List Files

ls -l /central_logs

Example output:

-rw-r--r-- 1 user1 user1 23 May 13 15:00 user1_log.txt
-rw-r--r-- 1 user2 user2 23 May 13 15:01 user2_log.txt

📘 Real-World Use Cases

• Log aggregation from multiple users/applications
• Shared reporting directory
• Assignment submissions in training environments
• Secure drop folders in enterprise settings.

🧠 Bonus Tips

• Use ACLs (Access Control Lists) for even more granular permission control
• Monitor file activity using tools like auditd or inotify

📌 Conclusion

This setup offers a simple yet powerful way to allow multiple users to collaborate by writing to a shared directory without compromising file integrity or security. Sticky Bit is your friend in scenarios like this!