What does the fourth octal digit mean?

It encodes the special bits — setuid (4), setgid (2), and sticky (1). It only appears when one of those is set, e.g. 4755.

What do s, S, t, and T mean in the symbolic form?

They show special bits: s/S for setuid/setgid and t/T for the sticky bit. The letter is lowercase when the underlying execute bit is also set, uppercase when it is not.

chmod Permission Calculator

Calculate Unix file permissions visually. Tick read, write, and execute for owner, group, and others and get the octal (e.g. 750) and symbolic (rwxr-x---) forms instantly — including setuid, setgid, and sticky bits. Type an octal value to work backwards.

How to use chmod Permission Calculator

Check the permissions you want in the grid.
Read off the octal, symbolic, and ready-to-run chmod command.
Or type an octal value to set the checkboxes automatically.

Frequently asked questions

What does the fourth octal digit mean?: It encodes the special bits — setuid (4), setgid (2), and sticky (1). It only appears when one of those is set, e.g. 4755.
What do s, S, t, and T mean in the symbolic form?: They show special bits: s/S for setuid/setgid and t/T for the sticky bit. The letter is lowercase when the underlying execute bit is also set, uppercase when it is not.

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