Chmod / Permission Calculator
Toggle read, write, execute permissions for owner, group, and others. Get the octal value, symbolic notation, and chmod command instantly.
chmod 755 rwxr-xr-xOwner: read, write, execute
Group: read, execute
Others: read, execute
Frequently Asked Questions
What does chmod mean?
chmod stands for 'change mode' — a Unix command that modifies the read, write, and execute permissions of files and directories. Every file on a Unix-like system (Linux, macOS) has three permission sets: one for the owning user, one for the owning group, and one for everyone else (others).
What is the difference between octal and symbolic notation?
Octal notation represents permissions as a three-digit number (e.g., 755), where each digit is the sum of read (4), write (2), and execute (1) for owner, group, and others respectively. Symbolic notation uses letters — rwx for read/write/execute and a dash for absent permissions — arranged as a nine-character string such as rwxr-xr-x. Both represent the same permissions; octal is shorter to type while symbolic is easier to read.
What do the common permission values mean?
755 (rwxr-xr-x) is the standard for executable files and directories — owner can do everything, group and others can read and execute. 644 (rw-r--r--) is typical for regular files — owner can read and write, everyone else can only read. 600 (rw-------) restricts access entirely to the owner, suitable for private key files. 777 grants full permissions to everyone and should be avoided in production.
Why do file permissions matter?
Incorrect permissions are a common security vulnerability. Setting a private key or config file to 777 means any user on the system can read or modify it. Web servers, SSH, and many other tools will refuse to use files with overly permissive settings. Using the correct permissions limits the blast radius of a compromised account or process.