Day 6 : File Permissions and Access Control

Hello everyone! On Day 6 of my #90DaysOfDevOps challenge, I learned about file permissions and access control lists (ACL) in Linux. These are crucial concepts for managing who can access and change files on a system. Here’s what I did today:

What Are File Permissions? 🛡️

In Linux, every file has permissions that decide who can read, write, or run it. There are three categories of users:

1. Owner: The person who created the file.

2. Group: Other users who have special access to the file.

3. Others: Everyone else who uses the system.

Tasks for the Day:

1. Create a File and Check Permissions

I created a simple file and used this command to check the permissions:

ls -ltr

This showed me who can access the file and what they can do with it.

2. Change Ownership and Permissions

• I used chown to change who owns the file:

chown newowner filename.txt

• I used chgrp to change the group permissions:

chgrp newGroup filename.txt

• I used chmod to change the file's permissions. For example, to give only the owner read and write permissions:

chmod 600 filename.txt

3. Learn About Access Control Lists (ACL)

ACLs give more detailed control over who can access files. I used these commands:

• Set permissions for a specific user:

setfacl -m u:username:rwx my_directory

• Check the ACL permissions:

getfacl my_directory

Extra Tasks:

4. Change Permissions for Multiple Files

I wrote a script to change permissions for all files in a directory at once:

#!/bin/bash 
echo "Enter permission (e.g., 755):" 
read perm 
chmod $perm * 
echo "Permissions updated for all files."

5. Set ACL for a User via Script

Another script I made sets ACL permissions for a user on a file:

#!/bin/bash 
echo "Enter the filename:" 
read filename 
echo "Enter the username:" read username 
setfacl -m u:$username:rw $filename 
echo "ACL set for $username on $filename."

6. Learn About Sticky Bit, SUID, and SGID

I explored some special permissions:

• Sticky Bit: Only the file owner can delete files in a directory.

chmod +t /shared/directory

• SUID: Files can run with the file owner’s permissions.

chmod u+s /usr/bin/someprogram

• SGID: Files in a directory inherit the group of that directory.

chmod g+s /shared/directory

Backup and Restore File Permissions 💾

I also wrote scripts to back up and restore file permissions:

• Backup permissions:

ls -l > permissions_backup.txt

• Restore permissions:

while read line; do chmod $line; done < permissions_backup.txt

---

Final Thoughts🎶

Today’s tasks were all about controlling file access in Linux, which is super important for keeping systems secure. I’m learning so much as I continue this journey!