Quickly calculate and understand Unix/Linux file permissions with our free chmod calculator.
Simply select the permissions you need to instantly generate octal notation, symbolic representation, and chmod commands.
Chmod (change mode) is a Unix and Linux command used to change the access permissions of files and directories. It controls who can read, write, or execute a file. Understanding and properly setting file permissions is crucial for system security and proper file access management.
Using our chmod calculator is simple and straightforward:
Select Owner Permissions: Choose read, write, and execute permissions for the file owner
Select Group Permissions: Set permissions for users in the same group
Select Others Permissions: Configure permissions for all other users
View Results: Instantly see the chmod number (e.g., 755) and full command
Copy Command: Click the copy button to use the chmod command in your terminal
Unix and Linux file permissions are divided into three categories:
Owner (User): The person who owns the file
Group: Users who are members of the file's group
Others (World): All other users on the system
Each category can have three types of permissions:
Read (r): Permission to read or view the file content (value: 4)
Write (w): Permission to modify or delete the file (value: 2)
Execute (x): Permission to run the file as a program (value: 1)
777 (rwxrwxrwx): All permissions for everyone (not recommended for security)
755 (rwxr-xr-x): Owner has full control, others can read and execute
644 (rw-r--r--): Owner can read/write, others can only read
600 (rw-------): Only owner can read and write
750 (rwxr-x---): Owner full control, group can read/execute, others no access
700 (rwx------): Only owner has full control
444 (r--r--r--): Everyone can only read (write-protected)
400 (r--------): Only owner can read
Chmod uses octal (base-8) notation where each digit represents permissions for owner, group, and others respectively. The digit is calculated by adding:
4 for read permission
2 for write permission
1 for execute permission
0 for no permission
For example, chmod 755 means:
7 (4+2+1): Owner has read, write, and execute
5 (4+0+1): Group has read and execute
5 (4+0+1): Others have read and execute
Besides octal notation, chmod also supports symbolic notation:
u = user/owner, g = group, o = others, a = all
Operators: + (adds), - (removes), = (sets exact)
Examples: chmod u+x filename (adds execute for owner); chmod o=r filename (sets others to read-only).
Eliminating calculation errors when converting permissions to octal
Providing instant visual feedback and ready-to-use commands
Helping beginners understand structures and saving time for pros
Reducing security risks from incorrect permissions
Follow the principle of least privilege:
Never use 777 unless absolutely necessary
Use 644 for regular files and 755 for directories/scripts
Use 600 or 400 for sensitive configuration files
Regularly audit permissions for security vulnerabilities
Permissions work differently for directories:
Read (r): Allows listing directory contents
Write (w): Allows creating, deleting, or renaming files
Execute (x): Allows accessing/entering the directory
chmod 644 document.txt — Readable by all, writable by owner
chmod 700 ~/.ssh — Secure SSH directory
chmod -R 755 /var/www/html — Recursively set permissions for web directory
Permission Denied: Check read/execute permissions
Script Won't Execute: Ensure chmod +x is set
Web Server 403 Error: Verify files are 644 and directories are 755
Instant calculation with a visual selection interface
Octal and symbolic notation display
Privacy-focused: calculations are done in your browser
Chmod 755 gives the owner read, write, and execute permissions (7), while group and others get read and execute permissions (5 each). This is commonly used for executable files and directories.
644 is for regular files (owner can modify, others can read), while 755 is for executables and directories (owner can modify, others can read and execute).
Yes, chmod 777 gives everyone full permissions and is a security risk. It should be avoided except in specific temporary testing scenarios.
Use the command: ls -l filename
Chmod is specific to Unix/Linux systems. Windows uses a different permission system (ACLs).
Typically 644 for HTML/PHP files and 755 for directories. Never use 777 for web-accessible files.
Use the -R flag: chmod -R 755 /path/to/directory
Umask sets default permissions for newly created files. It works inversely to chmod - it specifies permissions to be removed.
Our chmod calculator makes it easy to calculate and understand Unix and Linux file permissions. Whether you're securing sensitive files, setting up web server permissions, or managing system files, this tool helps you generate the correct chmod commands quickly and accurately. Bookmark this page for quick access whenever you need to work with file permissions.