What do chmod values like 755 and 644 mean?

Each digit maps to owner, group, and other permissions. 7 means read+write+execute, 6 means read+write, 5 means read+execute, 4 means read only. So 755 is rwx for owner and r-x for group/other; 644 is rw- for owner and r-- for group/other.

What is symbolic notation for file permissions?

Symbolic notation uses rwx groups, such as rwxr-xr-x. It can also be expressed as u=rw,g=r,o=r style directives. Octal notation is compact for scripting; symbolic notation is human-readable for audits.

What permissions are usually safe for files and folders?

Common defaults are 644 for regular files and 755 for directories, depending on environment and ownership strategy. Executable scripts often use 755. Avoid overly permissive settings like 777 unless absolutely required and short-lived.

Why does incorrect chmod break deployments?

If permissions are too strict, apps cannot read config, write cache, or execute scripts. If too open, you increase security risk. Correct permissions are necessary for both runtime stability and least-privilege security practices.

Free tools

Free Chmod Calculator

Calculate chmod permissions with checkbox controls and convert between octal values and symbolic notation.

Copy-paste outputs

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Tool 01

Chmod Calculator

Convert Unix file permissions between octal and symbolic notation.

How it works

Chmod Calculator: methodology and worked example

How this tool computes its result

Models Unix file permissions as a 3×3 grid (owner/group/other × read/write/execute) of checkboxes. The octal digit for each scope is the sum of fixed weights for its checked permissions (read=4, write=2, execute=1); the symbolic string is built as "rwx"/"r-x"/etc. per scope directly from the same checkbox state. It also works in reverse: typing a 3-digit octal string (non-0-7 characters are stripped as you type and input is capped at 3 characters) and clicking Apply decodes each digit back into checkboxes using a bitwise AND against 4, 2, and 1.

Worked example

Starting from the tool's default state — owner read/write/execute all on, group and other read+execute on but write off — the octal readout is "755" and the symbolic readout is "rwxr-xr-x." Typing "644" into the octal box and clicking Apply decodes digit 6 for owner (6 & 4 = read on, 6 & 2 = write on, 6 & 1 = execute off → "rw-") and digit 4 for both group and other (4 & 4 = read on, write and execute off → "r--" each), producing the symbolic string "rw-r--r--" and updating the "Copy chmod command" button to copy "chmod 644 <file>".

When not to use this tool

It only covers the standard three-scope, three-permission octal model — there's no support for the special setuid/setgid/sticky bit (the leading fourth digit), symbolic modification syntax like u+x or go-w, or recursive/directory-vs-file semantics.

Common mistakes

- Typing an octal value that isn't exactly 3 digits (e.g. "75" or "7550") — the Apply button stays disabled until the input field holds exactly 3 characters, so partial input does nothing rather than applying a partial permission set.
- Entering digits outside the 0-7 octal range — the input handler strips any character that isn't 0-7 as you type, so typing "895" silently becomes "95" while waiting for one more valid digit, with no visible error.
- Toggling individual checkboxes and expecting the octal text field to update automatically — it doesn't; the octal/symbolic summary panel reflects live checkbox state, but the octal input box itself keeps whatever you last typed until you click Apply again.

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