Chmod calculator
Toggle Unix permission bits and inspect exact octal, symbolic and special-bit representations.
How it works & useful details
How it works & supported syntax
Toggle read(4), write(2) and execute/search(1) bits for owner, group and others. The leading optional octal digit encodes setuid(4), setgid(2) and sticky(1). Uppercase S or T means the special bit is set while execute is absent.
This calculates mode bits only. File type, ownership, ACLs, mount options and platform rules affect actual access. In particular, numeric chmod behavior for existing directory special bits varies. No file permissions are changed.
Local workspace
Your input stays in this page. These tools calculate or process text; they do not run commands, start containers, contact servers or change settings on your device.
Previews pause above 20,000 combined characters. Use the action to process the full supported input. Exports contain the complete result within the tool’s stated limits.
About this tool
Chmod calculator lets you toggle Unix permission bits for owner, group, and others, then shows the exact octal and symbolic representations plus the special bits. It prevents the usual mistakes when setting file modes by hand.
The tool does not touch any file on your system: it only computes the notation from the bits you select. Use the result in your own chmod command or deployment script.
How to use it
- Toggle read, write, and execute for owner, group, and others.
- Set special bits such as setuid, setgid, or sticky if you need them.
- Read the octal, symbolic, and special-bit forms.
- Copy the notation into your chmod command or configuration.
Worked examples
- 755 = rwxr-xr-x: the owner can read, write, and execute. Group and others can read and execute. This is the usual mode for directories and scripts.
- 644 = rw-r--r--: the owner can read and write, everyone else can only read. This is the usual mode for regular files.
- 600 = rw-------: only the owner can read and write. Use it for SSH private keys and files containing secrets. ssh refuses keys that are more open than this.
- 4750 = rwsr-x---: setuid plus 750. The program runs with the file owner's privileges, and others have no access.
Each octal digit is the sum of read (4), write (2), and execute (1) for one class: owner, group, others. So 7 = 4 + 2 + 1 and 5 = 4 + 1.
Special bits and directories
The optional leading digit sets the special bits: setuid (4) runs a program as its owner, setgid (2) runs it as its group or makes new files in a directory inherit the directory's group, and sticky (1) on a shared directory such as /tmp stops users from deleting each other's files. In symbolic form they replace the x with s or t. A capital S or T means the special bit is set without execute, which is usually a mistake.
On directories, execute means "search": you need it to enter the directory or access anything inside, even if you can read the listing. Avoid 777 on anything reachable by a web server. It lets every local user and process change the files.
Frequently asked questions
What do the special bits do?
Setuid and setgid change the effective user or group for execution, and the sticky bit restricts deletion inside shared directories. They are rarely needed and should be applied deliberately.
Why is a directory execute bit different from a file execute bit?
On directories, execute means the ability to enter or traverse the directory rather than to run it as a program.
Does this change permissions on my machine?
No. It is a calculator; you run the resulting command yourself.