PermCalc

Chmod Calculator

Decode octal permissions — see exactly who can read, write, and execute.

Octal permissions (e.g. 755)

What you entered

Octal: 755

1
Owner permissions
7 → read(yes) write(yes) exec(yes)= rwx
2
Group permissions
5 → read(yes) write(no) exec(yes)= r-x
3
Others permissions
5 → read(yes) write(no) exec(yes)= r-x
4
Full symbolic notation
chmod 755= rwxr-xr-x

Result

Symbolic: rwxr-xr-x

chmod 755 sets permissions to rwxr-xr-x: owner gets rwx, group gets r-x, others get r-x. Each octal digit encodes read (4), write (2), and execute (1).

Common chmod values and what they permit

Each digit is a sum: read is 4, write is 2, execute is 1. The three digits set owner, group, and everyone else in that order.

Octal	Symbolic	Owner	Group	Others	Typical use
777	rwxrwxrwx	rwx	rwx	rwx	Everyone can do anything - avoid
775	rwxrwxr-x	rwx	rwx	r-x	Shared group directory
755	rwxr-xr-x	rwx	r-x	r-x	Executables and directories
700	rwx------	rwx	---	---	Private directory
666	rw-rw-rw-	rw-	rw-	rw-	World-writable file - avoid
644	rw-r--r--	rw-	r--	r--	Normal file
600	rw-------	rw-	---	---	Private file, e.g. SSH keys
400	r--------	r--	---	---	Read-only private file

Directories need execute permission to be entered at all, which is why directories are 755 where the equivalent file would be 644. SSH refuses to use a private key that is not 600 or stricter.

What the three digits mean

Each octal digit represents a user class: owner, group, others. The digit is the sum of read (4) + write (2) + execute (1). So 7 = rwx (full access), 5 = r-x (read + execute), 4 = r-- (read only), 0 = --- (no access). 755 means owner has full access, everyone else can read and execute.

Common permission patterns

644 (rw-r--r--): default for files — owner reads/writes, others read only. 755 (rwxr-xr-x): default for directories and scripts — owner has full access, others can list/traverse. 600 (rw-------): private files like SSH keys. 777: everyone can do everything — almost never appropriate.

Frequently asked questions

I set my script to 644 and it won't run — why?

644 is rw-r--r-- — no execute permission for anyone. Scripts need execute permission: use 755 (rwxr-xr-x) so the owner can read, write, and execute, while others can read and execute.

What permission should my SSH key have?

600 (rw-------) — only the owner can read and write. SSH refuses to use a private key with group or world-readable permissions (644 or 755) because it's a security risk.

What does chmod 777 mean and why is it dangerous?

777 means rwxrwxrwx — everyone (owner, group, and all others) can read, write, and execute. On a web server, this lets any user modify your files. Use the minimum necessary permissions instead: 755 for directories, 644 for files.

How do I convert 'rwxr-xr-x' back to a number?

Read each group of three: rwx = 4+2+1 = 7, r-x = 4+0+1 = 5, r-x = 4+0+1 = 5. So rwxr-xr-x = 755. Enter either format in this calculator and it converts both ways instantly.