chmod Calculator
Convert between symbolic (rwxr-xr-x) and octal (755) Unix file permissions. Toggle owner/group/other bits, set setuid/setgid/sticky, and copy the chmod command.
| Read | Write | Execute | |
|---|---|---|---|
| Owner | |||
| Group | |||
| Other |
rw-r--r--chmod 644 filenameAbout this tool
Every file and directory on a Unix-like system carries a permission set
for three classes of user — the owner, the
group, and others — and three
operations: read, write, and
execute. This calculator lets you toggle each of the
nine bits and instantly see the octal number, the symbolic
rwx string, and the exact chmod command.
The octal form is the sum of three values per class: read is
4, write is 2, and execute is 1.
So rwx is 7, r-x is 5,
and rw- is 6. The most common modes are
644 for regular files (owner can edit, everyone can read) and
755 for directories and executables (owner can change,
everyone can traverse and run).
An optional leading digit holds the special bits:
setuid (4), setgid (2), and the sticky bit
(1). These change how execution and ownership behave and show
up in the symbolic string as s, s, and
t in place of the execute character. Because permission
mistakes are a frequent source of both broken deploys and security holes,
it helps to confirm the exact bits before running chmod on
anything important — especially anything world-writable.
Frequently asked questions
What does chmod 755 mean?
It sets read/write/execute for the owner (7 = 4+2+1) and read/execute for group and others (5 = 4+1). In symbolic form that is rwxr-xr-x. It is the typical mode for executables and directories you want others to enter and list but not modify.
What is the difference between octal and symbolic notation?
Octal is a 3- or 4-digit number where each digit is the sum of read (4), write (2), and execute (1) for owner, group, and other. Symbolic is the rwx string shown by ls -l. Both describe the same permission set; this tool shows them side by side and lets you edit either.
What are setuid, setgid, and the sticky bit?
They are the optional leading octal digit. setuid (4) makes an executable run as its owner; setgid (2) makes it run as its group or makes new files in a directory inherit the directory group; the sticky bit (1) on a directory (like /tmp) lets only a file owner delete their own files. In symbolic form they replace the execute character with s, s, and t.
Why does my permission show a capital S or T?
A capital S or T means the special bit is set but the corresponding execute bit is not. For example, setuid without owner-execute renders as rwSr--r--. It is usually a mistake — the special bit has no effect without execute.
Is anything sent to a server?
No. This is pure arithmetic that runs entirely in your browser. Nothing you toggle or type is transmitted.