tryb

tryb.dev / tool

Chmod Calculator

Convert Unix modes between octal and symbolic notation and surface risky write or privileged-execution bits.

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Transform chain

Apply an exact order locally. Each step receives the previous step's output.

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Unix modes encode read, write, and execute bits for owner, group, and other. A leading octal digit carries set-user-ID, set-group-ID, and sticky bits.

A mode is not the whole access decision. Ownership, directory traversal, umask, ACLs, capabilities, mount options, and platform policy can change effective access.

World-writable and privileged-execution bits deserve review but are not automatically vulnerabilities. Context distinguishes a shared sticky directory from a writable executable.

Edge cases worth knowing

Special execute notation
Symbolic s/S and t/T preserve whether the corresponding execute bit is also set.
Three versus four octal digits
755 and 0755 describe the same permissions; 4755 additionally sets set-user-ID.
Owner has no access
A valid mode can deny the owner while granting group or other access; tryb surfaces this unusual configuration.

Common mistakes

  • Using chmod 777 instead of correcting ownership or deployment policy.
  • Ignoring special bits because only the final three octal digits were reviewed.
  • Assuming the displayed mode includes ACLs, capabilities, or mount restrictions.
  • Confusing an octal mode with an ordinary decimal number.