chmod calculator
Octal ↔ symbolic Unix modes. Click bits or type 755 / 0644. Nothing is uploaded.
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How it works
A Unix file mode is a bit mask. Each of user / group / other has three bits: read (4), write (2), execute (1). Add them: rwx = 7, r-x = 5, rw- = 6.
An optional leading digit is the special bits: setuid (4), setgid (2), sticky (1). Symbolic form is 9 or 10 characters, e.g. rwxr-xr-x or rwsr-xr-x when setuid is on and user execute is on (S if execute is off).
chmod 755 file sets that mask. This page only explains the number; it does not change files on your machine.
Examples
644 rw-r--r-- files you edit; others read 755 rwxr-xr-x scripts / directories you own 600 rw------- private keys, .env 700 rwx------ private directory 4755 rwsr-xr-x setuid binary (rarely what you want) 1777 rwxrwxrwt /tmp sticky: anyone writes, only owner deletes
FAQ
What is 777? Everyone can read, write, and execute. Fine for a throwaway dir, a bad default for anything shared.
Why do directories need execute? On a directory, execute means “traverse / enter”. Without it you cannot cd or resolve a path inside, even if read is on.
setuid vs sticky? setuid runs a file as the owner. Sticky on a directory keeps delete rights with the file owner (like /tmp).
Is 0755 different from 755? Same mode. The leading zero is octal notation in C / some shells, not an extra bit.
Does this run chmod on a server? No. It only converts numbers and letters in the page.