Chmod Calculator

About Chmod Calculator

Unix file permissions control who can read, write, and execute a file. Permissions are set separately for the owner, the group, and everyone else, and are written either as a three-digit octal number such as 755 or in symbolic form such as rwxr-xr-x.

This calculator lets you toggle permissions visually and shows both the numeric and symbolic notation, ready to use with the chmod command. Being able to see both forms makes it easier to understand what a value like 644 actually grants.

Common use cases

• Working out the number for a permission set before running chmod.
• Decoding a value such as 750 to see who can do what.
• Choosing safe permissions for scripts, web files, and SSH keys.
• Teaching or reviewing Unix permissions.

Frequently asked questions

What does 755 mean?

The owner can read, write, and execute; the group and others can read and execute.

What permissions should an SSH private key have?

Typically 600, so only the owner can read and write it. SSH may refuse keys that are more open.

Is 777 ever a good idea?

Rarely. It lets every user modify the file and is a common source of security problems.

What are the special bits (the leading fourth digit)?

setuid (4xxx) runs the file as its owner, setgid (2xxx) runs it as its group, and the sticky bit (1xxx) restricts deletion in a shared directory to the file's owner.