chmod / File Permission Calculator

Enter permissions in any form — octal like 755, symbolic like rwxr-xr-x, or a chmod clause like u=rwx,go=rx — and get every other form back, along with what it actually allows.

Unsafe combinations are flagged. If you have been told to run chmod 777, read the warning before you do.

How it works

Every file on a Unix system carries nine permission bits, arranged as three groups of three. The groups are, in order, the owner of the file, the group it belongs to, and others — everyone else. Within each group the three bits are read (4), write (2) and execute (1), and the digit you see in 755 is simply those values added up: 7 is 4+2+1, 5 is 4+1.

What the execute bit means depends on what it is set on. On a file it means "this may be run as a program". On a directory it means something quite different: permission to traverse into it and reach what is inside. A directory with read but not execute lets you list the names of its contents and nothing else, which produces the memorable symptom of an ls that works and a cd that does not. This is why directories are normally 755 and files 644 — the directory needs its execute bit, the file does not.

Three further bits sit above the nine, shown as a leading fourth digit. setuid (4000) makes an executable run as its owner rather than the caller. setgid (2000) does the same for the group and, on a directory, makes new files inherit that directory's group — genuinely useful for shared folders. The sticky bit (1000) on a world-writable directory restricts deletion to each file's owner, which is what makes /tmp safe to share.

On a web server the rule of thumb is narrow: directories 755, files 644, and anything holding credentials — wp-config.php, .env — at 640 or 600. Scripts do not need the execute bit to be served by PHP; the interpreter reads them, it does not run them as programs. And 777 is almost never the answer. On shared hosting it means any other account on the machine can rewrite your code, and many servers now refuse to execute world-writable PHP at all, so it frequently makes the original problem worse.

Frequently asked questions