Chmod Calculator
Instantly convert Linux permissions between octal (e.g., 755) and symbolic (e.g., rwxr-xr-x) notation.
Chmod Calculator
Articles
Linux File Permissions
Chmod Symbolic Notation Explained: A More Readable Way to Set Permissions
Tired of memorizing octal codes like 755? Learn how chmod's symbolic notation (u,g,o,a) offers a more readable and precise way to manage Linux file permissions.
Linux File Permissions
How to Fix "chmod: operation not permitted" (3 Common Causes)
Stuck on the "chmod: operation not permitted" error? Our expert guide diagnoses the 3 common causes (ownership, immutability, read-only filesystems) and gives you the exact commands to fix it.
Linux File Permissions
How to Use Chmod Recursively (-R) Without Breaking Your Server
Learn how to use chmod -R safely. Our expert guide reveals the critical mistake most people make and shows you the correct find command to recursively change permissions.
Linux File Permissions
Chmod 777: What It Means & Why You Should Never Use It
Tempted to use 'chmod 777' to fix a permission error? Stop. A 15-year sysadmin explains the massive security risks and shows you the professional way to solve it.
Linux File Permissions
Chmod 644 Explained: The Secure Default for Your Web Files
Why do web files use 'chmod 644'? Our expert guide explains what it means, why it's the secure standard for files like HTML & images, and how to use it.
Linux File Permissions
Chmod 755 Explained: The Only Permission You Need for Web Servers?
Confused by 'Permission denied'? Our expert guide breaks down what 'chmod 755' means, why it's the standard for web servers, and when you should use it.
Understanding the Chmod Command
The `chmod` (change mode) command is a fundamental utility in Linux and Unix-like systems. It's the key to controlling who can read, write to, and execute your files and directories, forming the bedrock of your system's security and integrity.
What Permissions Are You Controlling?
Every file and directory has three basic permissions that you can assign to three different classes of users (Owner, Group, and Others).
- Read (r): The ability to view the contents of a file or list the contents of a directory.
- Write (w): The ability to modify or delete a file, or create and delete files within a directory.
- Execute (x): The ability to run a file as a program or script, or to enter (cd into) a directory.
Frequently Asked Questions (FAQ)
What do the numbers in chmod (like 755 or 644) mean?
The numbers are an octal (base-8) representation of the permissions. Each permission has a value: Read (r) = 4, Write (w) = 2, and Execute (x) = 1. You add these values together for each user class (Owner, Group, Others). For example:
- 755 (rwxr-xr-x): The most common setting for directories and executable files. Owner gets full permissions (4+2+1=7), while Group and Others can read and execute (4+0+1=5).
- 644 (rw-r--r--): The standard for non-executable files like web pages or text files. Owner can read and write (4+2+0=6), while everyone else can only read (4+0+0=4).
How do I make a file executable?
The simplest way is to add the execute permission for the user. Open your terminal and type the command: chmod +x your_script.sh. The `+x` flag adds the execute permission to the file for the owner, group, and others, allowing it to be run as a program.
Why do I get a "Permission Denied" or "Operation Not Permitted" error?
This usually happens for one of two reasons: 1) You are not the owner of the file and do not have the necessary permissions to change it, or 2) The file is owned by the root user. In most cases, you can solve this by using the `sudo` command to run `chmod` with administrative privileges, like this: sudo chmod 755 your_file.txt.