The Art of File Permissions – Guarding Your Secrets

In the land of Linux, files and directories have strict rules about who can read, write, and execute them. If you don’t understand these rules, you might accidentally expose your secrets—or lock yourself out!

Today, we unlock the mysteries of file permissions and ownership.

Understanding File Permissions

Run this command on any file:

ls -l

You'll see something like this:

-rwxr-xr--  1 noob users  1234 Mar 10  noob_script.sh

Breaking it down:

🔢 Position	🧐 Meaning
-	Type (file - or directory d)
rwx	Owner (user) permissions
r-x	Group permissions
r--	Others (everyone else)

Translation:

• The owner (noob) can read (r), write (w), and execute (x) the file.
• The group (users) can read and execute it.
• Everyone else can only read it.

Changing Permissions – Becoming a Gatekeeper

To change permissions, use chmod:

chmod u+x my_noob_script.sh  # Give the owner execute rights
chmod g-w my_noob_script.sh  # Remove write rights from the group
chmod o-r my_noob_script.sh  # Others can’t read it anymore!

If you need to grant full power:

chmod 777 my_noob_script.sh  # Warning: anyone can do anything!

Better idea:

chmod 755 my_noob_script.sh  # Owner: all, Group & Others: read & execute

The Magic of Numeric Permissions

Instead of rwx, you can use numbers:

🔢 Number	🎭 Permission
7	rwx (Read, Write, Execute)
6	rw- (Read, Write)
5	r-x (Read, Execute)
4	r-- (Read only)
0	--- (No permissions)

Example:

chmod 750 secret.txt

• Owner: Full control (7)
• Group: Read & execute (5)
• Others: No access (0)

Translation: Only the owner and their group can read/execute. Everyone else? No access! 🥷

Changing Ownership

Sometimes, files end up owned by the wrong user. To fix that:

sudo chown noob myfile.txt        # Give ownership to 'noob'
sudo chown noob:users myfile.txt  # Change owner & group

Special Permissions – The Secret Techniques

Sometimes, normal permissions aren’t enough. Meet setuid, setgid, and sticky bit!

🏆 Permission	🧐 Meaning
setuid (4)	Runs as the file owner (used for system commands like passwd)
setgid (2)	Runs with the group’s permissions (useful for shared directories)
sticky bit (1)	Only the owner can delete files in a directory (used in /tmp)

Examples:

chmod u+s my_noob_script.sh   # Enable setuid
chmod g+s shared_folder       # Enable setgid
chmod +t /tmp                 # Enable sticky bit