Chmod Calculator · Octal ⇄ Symbolic ⇄ chmod Command + setuid/setgid/sticky — Vectobox
Free chmod calculator: convert Linux file permissions between octal (755), symbolic (rwxr-xr-x), checkboxes and chmod commands. Correctly handles setuid/setgid/sticky special bits, capital S/T ineffective-bit warnings, and parses symbolic syntax like u+x,go-w. 100% browser, zero tracking.
Owner: Read, Write
Group: Read
Others: Read
Note: symbolic operations apply with no umask (a missing class defaults to a), and X adds execute only when any execute bit is already set. There is no filesystem context in the browser.
Chmod permissions in every format
Every Unix file permission is a 12-bit value: three special bits (setuid, setgid, sticky) plus read/write/execute for owner, group and others. This calculator keeps one mode as the single source of truth, so the checkbox matrix, octal (755 / 4755), symbolic ls -l string (rwxr-xr-x), binary, chmod commands and a plain-English description all stay in sync as you edit any one of them. Everything runs in your browser tab — nothing is uploaded.
setuid, setgid and the sticky bit
The high nibble holds three special bits. setuid (4000) runs an executable with the owner identity — the classic example is /usr/bin/passwd at 4755. setgid (2000) makes new files in a directory inherit its group, useful for shared folders at 2775. The sticky bit (1000) on a directory like /tmp at 1777 lets anyone create files but only the owner delete their own.
Symbolic operations (u+x, go-w, a=rx)
Beyond static permissions, chmod accepts symbolic operations: a class (u, g, o, a), an operator (+, -, =) and permissions (r, w, x, X, s, t). This tool parses comma-separated clauses such as u+x,go-w or u=rwx,go=rx and applies them to the current mode in order, exactly like chmod on the command line. The capital X adds execute only when an execute bit is already present.
Why capital S and T mean trouble
In an ls -l listing, a lowercase s or t means the special bit is set and the matching execute bit is also present — the bit works. A capital S or T means the special bit is set but the execute bit is missing, so the special bit has no effect. 4655 renders as rwSr-xr-x and 1666 as rw-rw-rwT. This calculator raises a clear warning whenever it detects an ineffective capital bit.
FAQ
- What is the difference between 3-digit and 4-digit octal?
- The 3-digit form (755) covers read/write/execute for owner, group and others. The 4-digit form (4755) adds a leading digit for the special bits: 4 = setuid, 2 = setgid, 1 = sticky, summed together. When no special bit is set the leading digit is 0 and is usually omitted.
- Why does ls show a capital S or T?
- A capital letter means the special bit is set but the corresponding execute bit is not. setuid without owner execute shows S, setgid without group execute shows S, and the sticky bit without other execute shows T. The bit is recorded but has no practical effect, which is why this tool warns about it.
- What does the symbolic operation field do?
- It applies a chmod symbolic change to the current mode. Type something like u+x to add owner execute, go-w to remove write from group and others, or u=rwx,go=rx to assign exact permissions. Press Enter or Apply and every other view updates from the new mode.
- Does this calculator use my umask?
- No. A browser has no filesystem context, so symbolic operations apply with no umask: an unspecified class defaults to a (all), and X adds execute only when an execute bit is already set. This keeps results predictable and matches what chmod would do given the same explicit input.
- Is any of this sent to a server?
- No. All parsing and rendering runs locally in your browser tab. Nothing is logged, stored, or transmitted.
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