Unix Permissions

Free Unix Permissions calculator with clear step-by-step results.

About Unix Permissions

Each permission class is a three-bit field where read is 4, write is 2 and execute is 1, so summing the bits per class gives the familiar three octal digits. The complementary umask is what a process would need so that newly created files default to this mode.

Formulas

Octal digit per class

Digit = 4 if read + 2 if write + 1 if execute

Umask

Umask = 777 - the resulting octal mode, digit by digit

Worked example

With the default values below, Unix Permissions returns Octal mode of 754. Change any input above and every figure here is recalculated in your browser.

Inputs used

Owner can read: Yes
Owner can write: Yes
Owner can execute: Yes
Group can read: Yes
Group can write: No
Group can execute: Yes
Others can read: Yes
Others can write: No
Others can execute: No

Results

Octal mode: 754
Symbolic mode: rwxr-xr--
Umask that produces this mode: 023
Security note: No obvious over-permission

Step by step

1Values used
2Octal digit per class
3Umask
4Octal mode= 754
5Symbolic mode= rwxr-xr--
6Umask that produces this mode= 023
7Security note= No obvious over-permission

Assumptions and limits

The result is derived only from the 9 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Permission changes on shared or production systems can create security exposures or break running services. Review changes carefully and prefer least privilege.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Permission changes on shared or production systems can create security exposures or break running services. Review changes carefully and prefer least privilege.

Frequently Asked Questions

What does execute mean on a directory?

It grants the right to traverse into the directory and access entries by name. Read without execute lets you list names but not stat or open them.

Why is world-writable dangerous?

Any user on the system can modify or replace the file. On a shared host that is a straightforward path to privilege escalation or data tampering.