How to Change File Permissions in Linux: Simple Guide

To change file permissions in Linux, use the chmod command followed by permission settings and the file name. Permissions can be set using symbolic (e.g., u+rwx) or numeric modes (e.g., 755).

Syntax

The basic syntax of the chmod command is:

• chmod [options] mode file

Here, mode defines the permissions to set, and file is the target file or directory.

Modes can be symbolic (like u+rwx) or numeric (like 755).

bash

chmod [options] mode file

Example

This example shows how to give the owner full permissions and others read and execute permissions on a file named script.sh using numeric mode.

bash

chmod 755 script.sh
ls -l script.sh

Output

-rwxr-xr-x 1 user user 0 Jun 10 12:00 script.sh

Common Pitfalls

Common mistakes include:

• Using incorrect numeric codes that don't match desired permissions.
• Forgetting to specify the file name.
• Not having the required permissions to change the file mode.
• Confusing symbolic operators like +, -, and =.

Example of wrong and right usage:

bash

chmod 777 script.sh  # Gives all permissions to everyone (usually unsafe)
chmod u=rwx,g=rx,o=rx script.sh  # Safer, explicit permissions

Quick Reference

Symbolic Mode	Meaning	Numeric Mode
u	User (owner)
g	Group
o	Others
r	Read permission	4
w	Write permission	2
x	Execute permission	1
+	Add permission
-	Remove permission
=	Set exact permission
7	rwx (read, write, execute)	7
6	rw- (read, write)	6
5	r-x (read, execute)	5
4	r-- (read only)	4
0	--- (no permission)	0

Key Takeaways

Use the chmod command with symbolic or numeric modes to change file permissions.

Numeric mode uses digits 0-7 to represent read, write, and execute permissions.

Symbolic mode uses letters u, g, o and operators +, -, = to modify permissions.

Always verify permissions with ls -l after changing them.

Avoid using overly permissive settings like 777 for security reasons.