Linux File Permissions Cheat Sheet

What Are File Permissions?

Linux file permissions control who can read, write, or execute a file or directory. They are set for three user groups:

• Owner: The file creator.
• Group: A user group that can access the file.
• Others: All other users.

Viewing File Permissions

Use the ls -l command to display file permissions:

ls -l

Example Output:

-rwxr-xr-- 1 user group 1234 Nov 16 14:00 file.txt

Permission Breakdown

Each permission has three parts:

[Type][Owner][Group][Others]

Changing File Permissions

1. Using chmod (Symbolic Mode):
   

   
   chmod [permissions] [file]
   
   

   Example: Add execute permission to the owner:
   

   
   chmod u+x file.txt
   
   

   Symbol	Meaning
   u	User (owner).
   g	Group.
   o	Others.
   a	All (user, group, others).

   Actions:

   Symbol	Action
   +	Add permission.
   -	Remove permission.
   =	Set exact permission.

   Example: Remove write permission for others:
   

   
   chmod o-w file.txt
   
   

1. Using chmod (Numeric Mode):

   Each permission level is represented by a number:

   Permission	Value
   r (read)	4
   w (write)	2
   x (execute)	1
   - (none)	0

   Combine values to set permissions:

   Owner (u)	Group (g)	Others (o)	Command
   rwx (7)	r-x (5)	r-- (4)	chmod 754 file.txt

Changing Ownership

1. Change file owner:
   

   
   chown [owner] [file]
   
   

   Example:
   

   
   sudo chown user file.txt
   
   

2. Change group:
   

   
   chown :[group] [file]
   
   

   Example:
   

   
   sudo chown :staff file.txt
   
   

3. Change both owner and group:
   

   
   chown [owner]:[group] [file]
   
   

   Example:
   

   
   sudo chown user:staff file.txt
   
   

Recursive Changes

To apply changes to all files and directories:

1. Change permissions recursively:
   

   
   chmod -R [permissions] [directory]
   
   

   Example:
   

   
   chmod -R 755 /path/to/folder
   
   

2. Change ownership recursively:
   

   
   chown -R [owner]:[group] [directory]
   
   

   Example:
   

   
   sudo chown -R user:staff /path/to/folder
   
   

Testing Permissions

Create a test file or directory to practice:

touch test.txt
chmod 600 test.txt  # Owner can read/write, others denied.
chmod 755 test.txt  # Everyone can read, owner can write.
chmod -R 770 /test  # Owner/group full access, others denied.