Convert Unix permissions between symbolic and octal

Unix permissions are compact, but switching between forms can be surprisingly error-prone when you are reviewing a deployment, writing a chmod command, or documenting a security change. This converter accepts either a nine-character symbolic value such as rwxr-xr-- or a three-digit octal value such as 754, validates every position, and returns both representations. The conversion is deterministic and runs without network access, filesystem access, or interpretation of the permission against a real file. Malformed digits, misplaced letters, extra prefixes, whitespace, and incomplete values produce an explicit input error instead of a plausible but incorrect result.

Understand the two permission representations

A standard Unix permission value describes access for three audiences in a fixed order: the file owner, the owning group, and everyone else. Symbolic notation gives each audience a three-character block. The positions always mean read, write, and execute, so rwx grants all three permissions, r-x grants read and execute, and r-- grants read alone.

Octal notation compresses those same bits into one digit per audience. Read contributes four, write contributes two, and execute contributes one. Adding the enabled values produces a digit from zero through seven.

Therefore rwx becomes 7, r-x becomes 5, and r-- becomes 4, making rwxr-xr-- equivalent to 754. This converter preserves that exact owner-group-other ordering. It does not look up users, groups, access-control lists, or filesystem metadata.

Keeping the operation narrowly focused makes the result predictable and useful in scripts, reviews, runbooks, and educational material where a clear representation change is all that is needed.

Provide a strict symbolic or octal value

Enter exactly one permission string in the text field. For octal input, provide exactly three characters and use digits zero through seven, for example 640 or 755. For symbolic input, provide exactly nine characters, divided conceptually into owner, group, and other triplets.

Each triplet must place r in the read position, w in the write position, and x in the execute position; use a hyphen when that permission is absent. A value such as rw-r----- is valid, while wr-r----- is not, because the letters are in the wrong positions. Validation is intentionally strict.

The converter does not trim spaces, accept a chmod command, accept a leading file-type character from an ls listing, or silently discard a leading zero. It also excludes setuid, setgid, and sticky-bit notation because those special bits require additional symbolic rules. Rejecting unsupported forms prevents accidental normalization and makes malformed input visible immediately, which is safer when permission values are copied into deployment automation.

Use the result safely in operational work

The response identifies whether the submitted value was octal or symbolic and returns normalized fields for both forms. You can show the symbolic field to a reviewer who wants readable access rights, while using the octal field in a command, infrastructure template, or configuration record. Always remember that conversion is not authorization analysis.

A mathematically correct mode can still be inappropriate for a sensitive key, shared directory, executable, or service account. Before applying it, confirm who owns the target, whether directory execute permission is required for traversal, whether default ACLs add access, and whether the application expects special permission bits. This tool never changes a file and never claims that a mode is secure; it only converts a supplied value.

That separation is useful for change-control workflows because teams can validate formatting and compare representations before any privileged command runs.