Chmod Calculator
🔒 Runs in your browser
| Read | Write | Execute | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Other |
How Unix permissions work
Every file and directory carries permissions for three classes — the owner, the group and others — each with three flags: read, write and execute. The calculator keeps the checkbox grid, the octal number and the symbolic string in sync, so you can edit whichever representation you find clearest and read off the rest.
Octal and symbolic notation
In octal, each class is one digit built from read = 4, write = 2 and execute = 1. Add them up:
7 is rwx, 6 is rw-, 5 is r-x. The three digits
owner-group-other give familiar modes like 644 for files and 755 for
directories and scripts. The symbolic form spells the same nine flags out as
rwxr-xr-x.
Setuid, setgid and the sticky bit
An optional fourth leading digit carries the special bits: setuid = 4, setgid = 2, sticky = 1.
In symbolic notation they replace the execute letters — s or t when
execute is also set, uppercase S or T when it is not. Everything runs
in your browser as plain arithmetic; nothing is uploaded.
Frequently asked questions
How do octal and symbolic permissions relate?
Each octal digit encodes one triplet: read is 4, write is 2, execute is 1. So 7 is rwx, 5 is r-x and 4 is r--; the digits owner-group-other give 755 or rwxr-xr-x.
What are the setuid, setgid and sticky bits?
They are the optional leading fourth octal digit: setuid is 4, setgid is 2, sticky is 1. In symbolic mode they fold into the execute slots as s, s and t (S/T when execute is off).
What does chmod 755 mean?
The owner may read, write and execute; group and others may read and execute but not write. It is the usual mode for directories and executable scripts.
Is my input sent anywhere?
No. The conversion is plain arithmetic that runs entirely in your browser. Nothing is uploaded or stored.