chmod Calculator

Check the permission bits, or type an octal mode. The symbolic form updates with it.

Read Write Execute Owner Group Other

What the mode means

A Unix file mode is nine rwx bits, plus setuid, setgid and the sticky bit. This page keeps the checkboxes, the octal number and the symbolic string on the same mode.

How to use it

  1. The grid is Owner, Group and Other, each with Read, Write and Execute. setuid, setgid and Sticky sit under the grid. The page opens at 644, symbolic rw-r--r--.
  2. Checking a box updates Octal and Symbolic. Typing 3 or 4 octal digits updates the boxes.
  3. The presets are 644, 755, 600, 700 and 777.
  4. Show Example sets Octal to 755 and Symbolic to rwxr-xr-x.
  5. Clear All sets 000 and ---------. Copy Result copies the symbolic string.

Octal and letters

Three digits are owner, group and other. A fourth digit on the left is setuid (4), setgid (2) and sticky (1). 4755 is rwsr-xr-x, 2755 is rwxr-sr-x, and 1755 is rwxr-xr-t.

When the execute bit is off, setuid or setgid is S and sticky is T. Digits must be 0 through 7. 888 is an error. A special bit makes the octal field four digits.

Where people use it

  • Checking that 755 is rwxr-xr-x before a chmod command.
  • Reading a four-digit mode that includes setuid.
  • Starting from 600 for a file only the owner should read.

Questions

Why is 644 not executable?

644 sets read and write for the owner, and read for group and other. Execute stays off.

Does this change a file on the server?

It only prints the mode. The chmod command is still run on the machine that has the file.