Chmod Calculator

Calculate Unix file permissions

This chmod calculator converts between the three ways Unix and Linux describe file permissions: the checkboxes you tick, the three-digit octal number such as 755 or 644, and the symbolic string such as rwxr-xr-x. Editing any of them updates the others live, so you can start from whichever representation you already have. The result includes a ready-to-paste chmod command line.

Permissions are grouped into three classes — owner (the user who owns the file), group (users in the file’s group), and others (everyone else) — and each class has three bits: read (r = 4), write (w = 2), and execute (x = 1). Adding the bits for a class gives its octal digit, so rwx = 7, r-x = 5, and rw- = 6. Common modes are 644 for regular files (owner can edit, everyone can read) and 755 for scripts and directories (owner can edit, everyone can read and run).

FAQ

What does chmod 755 mean? The owner gets read, write, and execute (7); the group and others get read and execute (5 and 5). It is the typical mode for executable scripts and for directories you want others to enter.

What is the difference between 644 and 755? Both give the owner read and write, but 755 also adds the execute bit for everyone, which is what makes a file runnable or a directory listable. Use 644 for data and text files, 755 for programs and folders.

How does octal map to rwx? Each digit is the sum of read (4), write (2), and execute (1) for one class. So 7 = 4+2+1 = rwx, 6 = 4+2 = rw-, 5 = 4+1 = r-x, and 0 = no permissions.

Why does the execute bit matter for directories? On a directory, the execute bit grants permission to enter it and access files inside, rather than to run it. A directory usually needs execute wherever it has read, which is why 755 is common for folders.