Linux chmod Command

last modified March 3, 2025

The chmod command in Linux is used to change file permissions. It allows users to control who can read, write, or execute a file. This tutorial covers basic and advanced usage of chmod with examples.

File permissions in Linux are represented by three types: read (r), write (w), and execute (x). These permissions are assigned to three categories: owner, group, and others.

Basic Syntax

The basic syntax of chmod is:

chmod [options] permissions filename

permissions can be specified using symbolic or numeric notation.

Example 1: Change Permissions Using Symbolic Notation

This example adds execute permission for the owner of a file.

chmod u+x filename.txt

Here, u stands for the owner, and +x adds execute permission.

Example 2: Change Permissions Using Numeric Notation

This example sets read, write, and execute permissions for the owner, and read-only permissions for others.

chmod 744 filename.txt

The number 744 represents rwxr--r-- in permissions.

Example 3: Remove Write Permission for Group

This example removes write permission for the group.

chmod g-w filename.txt

Here, g stands for the group, and -w removes write permission.

Example 4: Recursively Change Permissions

This example changes permissions for all files and directories within a folder.

chmod -R 755 /path/to/directory

The -R option applies the changes recursively.

Example 5: Set Permissions for Owner and Group

This example sets read and write permissions for the owner and group.

chmod ug=rw filename.txt

Here, ug refers to the owner and group, and =rw sets read and write permissions.

Example 6: Set Default Permissions with umask

This example uses umask to set default permissions for new files.

umask 022

The umask value 022 ensures new files have rw-r--r-- permissions.

Best Practices for chmod

• Use Numeric Notation: Use numeric notation for precise control over permissions.
• Be Cautious with Recursive Changes: Use -R carefully to avoid unintended changes.
• Check Current Permissions: Use ls -l to verify permissions before making changes.
• Limit Execute Permissions: Only grant execute permissions when necessary for security.

Source

GNU chmod Manual

In this article, we have explored various examples of using the chmod command to manage file permissions, including symbolic and numeric notation.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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