MundoKit

Chmod calculator

Enter an octal starting mode and optional symbolic changes. See the resulting bits, readable permissions and an explicit chmod command.

Inputs
One to four octal digits. Exact bits; no directory preservation rules.
Explicit u, g, o or a required. Examples: u+x,g-w or g=u. Empty means inspect only.

Results

Resulting octal mode
0744
Symbolic permissions
rwxr--r--
Explicit mode command
chmod 0744 PATH
Permission bits
ClassReadWriteExecute / search
OwnerYesYesYes
GroupYesNoNo
OthersYesNoNo
  • setuid: off; setgid: off; sticky: off.
  • GNU symbolic calculation, including directory setuid/setgid preservation. OS policy, ownership, ACLs and filesystem restrictions may change the actual effect. Directory =mode uses the GNU explicit-reset syntax.

Results update as you type. The share link stores your inputs after the # in the address, which is not sent to our server, but anyone you send it to can read them.

How it works

Each octal permission digit adds read = 4, write = 2 and execute = 1. The three low digits describe owner, group and others. A leading digit adds setuid = 4, setgid = 2 and sticky = 1. On executable files, setuid and setgid request the file owner or group as the effective identity on execution. The sticky bit restricts directory entry removal. These are exact bit operations, so no rounding occurs.

Symbolic clauses run left to right against the current mode. Explicit u, g, o or a is required, avoiding omitted-who umask effects. Operators +, - and = add, remove or replace the selected bits. Use rwx, conditional X, special s/t, or one copy letter such as g=u. X adds execute/search only for a directory or when at least one execute bit is already on. Commas separate clauses; chained operators such as u+r-w are accepted.

The starting octal number specifies exact initial bits. Symbolic changes follow GNU directory behavior: = preserves setuid and setgid unless s is explicitly included. Permission failures and filesystem side effects are not simulated. For directories, the generated command uses GNU =octal syntax to request the calculated final bits explicitly. Changes are limited to 4,096 characters and 100 clauses.

Worked examples

Add owner execute

Starting at 0644 (rw-r--r--), applying u+x adds the owner execute bit and yields 0744 (rwxr--r--).

Inspect setuid

Mode 4755 is rwsr-xr-x. The leading 4 sets setuid while owner permissions 7 include execute.

Frequently asked questions

What does chmod 755 mean?
Owner can read, write and execute; group and others can read and execute. Directories use execute as search permission.
What is the difference between s and S?
Lowercase s means setuid or setgid plus execute. Uppercase S means the special bit is set without its corresponding execute bit.
What does the sticky bit do?
On a directory it restricts removal or renaming of entries, normally to the entry owner, directory owner or a privileged process. It does not make a file private.
Why must I write a+x rather than +x?
Omitted-who symbolic modes depend on umask. Requiring an explicit class makes the result reproducible.
Does setgid mean the same thing on directories?
No. On directories it commonly causes new entries to inherit the directory group. Actual behavior depends on the system and filesystem.

Sources

Last reviewed 2026-11-14. The method is written out above so you can check our math.