How to Use chmod Command in Linux: Syntax and Examples

Use the chmod command in Linux to change file or directory permissions by specifying the permission mode and target file. The syntax is chmod [options] mode file, where mode can be symbolic (like u+r) or numeric (like 755).

Syntax

The basic syntax of the chmod command is:

• chmod: The command to change permissions.
• [options]: Optional flags like -R for recursive changes.
• mode: The permission settings, either symbolic (e.g., u+x) or numeric (e.g., 755).
• file: The file or directory to change permissions on.

bash

chmod [options] mode file

Example

This example shows how to give the owner execute permission on a file named script.sh using symbolic mode, and how to set full permissions for the owner and read-execute for group and others using numeric mode.

bash

touch script.sh
chmod u+x script.sh
ls -l script.sh
chmod 755 script.sh
ls -l script.sh

Output

-rw-r--r-- 1 user user 0 date script.sh
-rwxr--r-- 1 user user 0 date script.sh
-rwxr-xr-x 1 user user 0 date script.sh

Common Pitfalls

Common mistakes include:

• Using numeric mode without understanding what each digit means.
• Forgetting to use -R when changing permissions recursively on directories.
• Setting permissions too open (like 777) which can be a security risk.

Example of a wrong and right way:

bash

chmod 777 myfile.txt  # Too open, risky
chmod 755 myfile.txt  # Safer, common setting

Quick Reference

Permission	Symbolic	Numeric	Description
Read	r	4	Allows reading the file or listing directory contents
Write	w	2	Allows modifying the file or directory contents
Execute	x	1	Allows running the file or entering the directory
Owner	u	-	User who owns the file
Group	g	-	Users in the file's group
Others	o	-	Everyone else

Key Takeaways

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

Numeric mode uses three digits representing owner, group, and others permissions.

Use -R option to apply changes recursively to directories.

Avoid setting permissions to 777 to keep your system secure.

Check permissions with ls -l after changing them.