What does chmod 755 mean?

755 gives the owner read, write and execute (7 = 4+2+1), and the group and other read and execute only (5 = 4+1). It is the typical permission for directories and executable scripts that everyone may run but only the owner may change.

How is the octal value calculated?

Each scope adds read (4), write (2) and execute (1). So read plus write is 6, read plus execute is 5, and all three is 7. The three digits are owner, group and other in that order, optionally preceded by a fourth digit for the special bits.

What does chmod 644 mean?

644 gives the owner read and write (6 = 4+2), and the group and other read only (4). It is the standard permission for regular files that should not be executable, such as documents, images and config files.

What is the difference between octal and symbolic notation?

Octal uses three or four digits — each a sum of read 4, write 2 and execute 1 — for example 755. Symbolic spells out the same bits as a nine-character string like rwxr-xr-x. Both describe identical permissions, and this tool converts freely between them in either direction.

What are setuid, setgid and the sticky bit?

They are the fourth (leading) octal digit: setuid (4000) runs an executable as its owner, setgid (2000) runs it as its group or makes new files in a directory inherit the group, and the sticky bit (1000) on a shared directory like /tmp stops users deleting each other's files. In symbolic notation they show as s, s and t in the execute column (uppercase S or T when the underlying execute bit is off).

Does this tool send my permissions anywhere?

No. The calculator runs entirely in your browser, so nothing you select, type or copy is uploaded to any server.

Chmod Calculator — Gera Tools

The Unix chmod command sets file permissions, but its octal numbers are easy to get wrong and even easier to misread. This calculator removes the guesswork: tick read, write and execute for owner, group and other, and it instantly shows the octal value, the symbolic notation (rwxr-xr-x), the matching chmod command in both forms, and an ls -l style preview. It works in both directions — apply a preset, paste an octal value like 4755, or type a symbolic string like rwxr-xr-x and watch every checkbox snap into place. It also handles the three special bits (setuid, setgid and the sticky bit) that most online calculators ignore, so it is genuinely useful for real-world cases like setuid binaries and shared directories. Whether you are hardening a server, writing a deployment script, debugging a “permission denied” error, or just trying to remember what chmod 600 means, this gives you a correct, copy-ready answer in seconds.

How it works

Each of the three scopes (owner, group, other) gets one octal digit, formed by adding the permission bits it has: read = 4, write = 2, execute = 1. So read+write is 6, read+execute is 5, and all three is 7. The three digits are concatenated in the order owner-group-other. A fourth, leading digit encodes the special bits — setuid = 4, setgid = 2, sticky = 1 — and is shown only when one of them is set. Symbolic notation expresses the same nine bits as a string, with a letter (r, w, x) where the bit is set and a dash where it is not; special bits replace the relevant execute character with s, s or t (uppercase S/T when the execute bit underneath is off). When you type an octal or symbolic value, the tool parses and validates it, then mirrors it back through the checkboxes.

Permission	Octal	Symbolic
read	4	r—
read + write	6	rw-
read + execute	5	r-x
read + write + execute	7	rwx

Example

For owner = read+write+execute, group = read+execute, other = read+execute:

owner 4+2+1 = 7, group 4+1 = 5, other 4+1 = 5 → 755 → rwxr-xr-x → chmod 755 filename

This is the usual permission for directories and executable scripts. Add the setuid bit and the value becomes 4755 → rwsr-xr-x, the classic permission for a program that must run with its owner’s privileges. Presets cover everyday cases — 644 for files, 755 for executables and directories, 600 for private files, 640 for group-readable config, 1777 for a sticky shared directory like /tmp — and you can always fine-tune from there. Everything runs in your browser; nothing is uploaded.