Chmod Calculator
Convert Linux file permissions between different formats
Linux Permissions:
How to Use This Chmod Calculator
Check the desired boxes to set permissions for each user class (Owner, Group, Public). The calculator will automatically show you the numeric (octal) value, symbolic notation, and the chmod command.
Understanding Linux File Permissions
File permissions in Linux are managed in three distinct user classes: user/owner, group, and others/public. Each class can have read (r), write (w), and execute (x) permissions.
File permission can be represented in a symbolic (e.g., rwxr-xr--) or numeric (octal) format (e.g., 754).
What is a Linux Permissions Calculator?
A Linux permissions calculator is an online tool that helps you convert between different permission formats quickly and accurately. Instead of manually calculating chmod numbers, this file permissions calculator does the work for you, making it easier to change file permissions in Linux systems.
This tool is especially useful when you need to set precise permissions but aren't familiar with how octal permissions work or want to avoid errors when using the chmod command.
Understanding Linux Octal Permissions
Linux octal permissions use a three-digit number system where each digit represents permissions for owner, group, and others. Each permission has a numeric value:
- Read (r) = 4
- Write (w) = 2
- Execute (x) = 1
To calculate the permission value for each user class, simply add the numbers together. For example, read + write = 6, while read + write + execute = 7. This octal permissions calculator automatically performs these calculations as you select permissions.
Common Chmod Numbers Explained
- 755 - Owner can read, write, execute; Group and others can read and execute
- 644 - Owner can read and write; Group and others can only read
- 777 - Everyone has full permissions (not recommended for security)
- 600 - Only owner can read and write; No access for others
- 700 - Only owner has full permissions; No access for others
Linux Permissions Chart
This quick reference chart shows the most commonly used permission combinations in Linux systems:
| Octal | Symbolic | Description | Common Use |
|---|---|---|---|
| 777 | rwxrwxrwx | Full permissions for everyone | Avoid for security reasons |
| 775 | rwxrwxr-x | Owner and group have full access, others read/execute | Shared project directories |
| 755 | rwxr-xr-x | Owner has full access, others read/execute | Web directories, executable scripts |
| 750 | rwxr-x--- | Owner full access, group read/execute, no public access | Private scripts shared with team |
| 700 | rwx------ | Only owner has full access | Personal scripts and directories |
| 644 | rw-r--r-- | Owner can write, everyone can read | Regular files, web content |
| 640 | rw-r----- | Owner can write, group can read | Configuration files |
| 600 | rw------- | Only owner can read and write | Private files, SSH keys |
Use this calculator to convert any rwxr-xr-x format to its numeric equivalent, or vice versa. Understanding these permission patterns helps you secure your Linux system properly.
How to Change File Permissions in Linux
Changing file permissions in Linux is straightforward once you understand the chmod command. Here are practical examples you can use right away:
Basic Chmod Commands
chmod 755 script.sh- Sets executable permissions for a script (owner can modify, everyone can run)chmod 644 document.txt- Sets standard file permissions (owner can edit, others can read)chmod 600 private.key- Makes a file accessible only to the owner (common for SSH keys)chmod -R 755 /var/www/html- Applies permissions recursively to all files in a directory
Checking Current Permissions
Before changing permissions, it's good practice to check what they currently are:
ls -l filename- Shows permissions in symbolic format (rwxr-xr-x)stat filename- Displays detailed file information including octal permissionsls -la- Lists all files including hidden ones with their permissions
Using this chmod online calculator ensures you set the correct permissions before executing the command on your server. Simply select the desired permissions above, and copy the generated command.
Frequently Asked Questions
What does chmod 777 mean?
Chmod 777 gives full read, write, and execute permissions to everyone (owner, group, and public). While convenient, it's generally not recommended for security reasons as it allows anyone to modify or execute the file.
How do I check permissions of a file in Linux?
To check file permissions in Linux, use the ls -l filename command. This displays the permissions in symbolic format (like rwxr-xr-x). You can also use stat filename for more detailed information including the octal format. For directories, use ls -ld directory/ to check their permissions.
How do I convert rwxr-xr-x to a number?
To convert rwxr-xr-x to a number, break it into three groups of three characters. For rwxr-xr-x: rwx (4+2+1=7), r-x (4+0+1=5), r-x (4+0+1=5), giving you 755. Use this calculator to instantly convert any symbolic notation to its numeric equivalent.
How do I calculate Linux file permissions?
To calculate Linux file permissions, add the values for each permission type: Read (4) + Write (2) + Execute (1). Do this separately for owner, group, and public. This file permissions calculator automates the process for you.
What's the difference between 755 and 775 chmod?
With 755 chmod, the owner has full permissions (rwx), while group and others can only read and execute (r-x). With 775 chmod, both owner and group have full permissions (rwx), while others can only read and execute. Use 775 when you need to give write access to team members in the group.
What's the difference between symbolic and numeric permissions?
Symbolic notation uses letters (rwxr-xr--) while numeric notation uses three-digit octal numbers (754). Both represent the same permissions, but octal permissions are more commonly used with the chmod command.
Why use an octal permissions calculator?
An octal permissions calculator helps you avoid mistakes when setting file permissions. It visually shows which permissions are enabled and provides the correct chmod numbers, making system administration easier and reducing security risks.
Can I use this chmod online tool for server files?
Yes! This chmod online calculator helps you determine the correct permission values before applying them to your server files. Simply calculate the permissions here, then use the generated chmod command on your Linux server.
What are safe default permissions for files and directories?
For files, 644 is a safe default (owner can write, others can read). For directories, 755 is standard (owner has full access, others can read and navigate). For sensitive files, use 600 (only owner can access).
How do I check permissions in Linux using the command line?
The most common way to check permissions in Linux is using ls -l which shows permissions in symbolic format. For a more detailed view including octal permissions, use stat -c "%a %n" filename. To check multiple files at once, use ls -l /path/to/directory.