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About this tool
Convert Unix file permissions between numeric (755) and symbolic (rwxr-xr-x) form with a checkbox grid, setuid, setgid and sticky bits.
This calculator converts Unix file permissions between numeric octal form (755) and symbolic rwx form (rwxr-xr-x), using the POSIX weights read=4, write=2, execute=1 for each of owner, group and others, plus the setuid (4), setgid (2) and sticky (1) bits in a leading fourth digit. It is built for Linux and macOS users setting modes with chmod who want to see exactly what a number grants — with warnings for risky combinations like world-writable or setuid files.
Open Chmod Permission Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Type octal or symbolic, or tick the grid — all three stay in sync instantly.
Handles setuid, setgid and sticky, including the s/S and t/T distinction ls uses.
Flags world-writable files, setuid-plus-write holes and other modes that are almost never intended.
755 gives the owner read, write and execute (7 = 4+2+1), and gives group and others read and execute (5 = 4+1) — shown symbolically as rwxr-xr-x. It is the standard mode for directories and executable scripts that everyone may run but only the owner may change.
644 (rw-r--r--) lets the owner read and write while everyone else can read; 600 (rw-------) cuts off all access for group and others. Private material such as SSH private keys must be 600 — OpenSSH refuses keys that are readable by others.
The leading digit holds the special bits: setuid=4, setgid=2, sticky=1. 4755 sets setuid, so the program runs with the file owner's user ID regardless of who launches it — this is how passwd works. ls shows it as rwsr-xr-x, with s replacing the owner's x.
A capital letter means the special bit is set but the matching execute bit is not. Lower-case s or t means both are set. For example rw-r-Sr-- is mode 2644 — setgid on a file with no group execute — which is usually a mistake worth fixing.
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