Chmod Calculator
Build Unix file permissions visually and get the octal and symbolic notation for chmod.
| Role | Read (4) | Write (2) | Execute (1) |
|---|---|---|---|
| Owner | |||
| Group | |||
| Others |
chmod 755
-rwxr-xr-x
About the Chmod Calculator
Unix file permissions control who can read, write, and execute a file, split across three roles: the owner, the owning group, and everyone else. The chmod command sets them, most often using octal notation where each digit is the sum of read (4), write (2), and execute (1) for one role.
This calculator works in both directions: click the checkboxes to build a permission set and read off the octal, or click a preset to see what those familiar numbers (755, 644, 600) actually grant. The symbolic form, the rwxr-xr-x string that ls -l shows, updates alongside.
The presets cover the cases that matter: 755 for directories and executables (everyone can enter or run, only the owner can modify), 644 for regular files, 600 for private files like SSH keys, which refuse to work if permissions are looser. And 777, which grants everything to everyone and is almost always the wrong answer to a permissions problem.
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Frequently asked questions
What do 755 and 644 mean?
755 is rwxr-xr-x: the owner can do everything, everyone else can read and execute but not write. 644 is rw-r--r--: the owner can read and write, everyone else can only read. They are the standard permissions for executables/directories and regular files respectively.
Why does execute matter for directories?
For a directory, execute means "can enter it and access things inside." A directory with read but not execute lets you list names but not open anything. Directories almost always need execute wherever they have read.
Why is chmod 777 a bad idea?
It lets every user and process on the system modify the file. It "fixes" permission errors by removing all protection, including from malware and buggy scripts. The right fix is identifying which user needs access and granting only that.