Free Tool

Chmod Calculator

Toggle read, write, and execute permissions — or type an octal or symbolic value — and get the matching chmod command instantly. Runs entirely in your browser.

How the chmod calculator works

Every file and directory on Linux has three permission classes — owner, group, and others — and each class can independently allow read, write, and execute. Each permission has a fixed numeric weight: read is worth 4, write is worth 2, and execute is worth 1. Add up the values you want for a class and you get one octal digit; do that for owner, group, and others and you get the familiar three-digit mode, such as 644 or 755. The calculator above does this arithmetic for you the moment you check a box, type an octal value, or type a symbolic value — all three stay in sync.

Linux permission values

Since each digit is a sum of 4, 2, and 1, there are only eight possible combinations per class:

Digit	Symbolic	Meaning
`0`	`---`	No permissions
`1`	`--x`	Execute only
`2`	`-w-`	Write only
`3`	`-wx`	Write and execute
`4`	`r--`	Read only
`5`	`r-x`	Read and execute
`6`	`rw-`	Read and write
`7`	`rwx`	Read, write, and execute

Common chmod permissions

A handful of modes cover most real-world cases. What fits depends on the file and where it lives — none of these is a universal default:

Mode	Symbolic	Typical use
`600`	`rw-------`	Private files only the owner should read or edit — SSH private keys, credential files.
`644`	`rw-r--r--`	Regular files that others should be able to read but not modify — configs, static assets.
`700`	`rwx------`	Private directories and scripts, such as `~/.ssh`.
`755`	`rwxr-xr-x`	Directories and executables everyone should be able to run or enter, but only the owner should edit.
`775`	`rwxrwxr-x`	Shared directories where a whole group needs write access, such as a deploy user's group.

See what chmod 755 means and what chmod 600 means for more detail on the two most common modes, including when each one is (and isn't) the right call.

Avoid chmod 777. 777 gives every user on the system read, write, and execute access — including the ability to overwrite or replace the file entirely. It's occasionally used as a quick fix for a permissions error, but that usually just trades a permissions problem for a security one. If something needs broader access, work out which specific class (group or others) actually needs it and grant only that.

Numeric vs. symbolic permissions

The same permission set can be written two ways. 755 is the numeric (octal) form: one digit each for owner, group, and others. rwxr-xr-x is the symbolic form: the same information as nine characters, three per class, always in the order read, write, execute, with a dash standing in for any permission that's off. Tools like ls -l show the symbolic form; chmod accepts either.

Chmod examples

Command	Effect
`chmod 755 script.sh`	Owner can edit and run it; everyone else can only run it.
`chmod 644 config.conf`	Owner can edit it; everyone else can only read it.
`chmod 600 private-key`	Only the owner can read or write it — no one else has any access.

OpenSSH commonly rejects private keys that are accessible to other users, which is why 600 is a common safe mode for private key files on Unix-like systems. Widening permissions on a key to work around a "bad permissions" error defeats the point of the check. See our guide to correct SSH key permissions for the exact modes OpenSSH expects across your key files and ~/.ssh directory. Exact requirements can vary by program, filesystem, and ownership setup, so check the tool's own documentation if it disagrees.

Recursive chmod

Add -R to apply a mode to a directory and everything inside it: chmod -R 755 /var/www/html. Because -R applies the same mode to files and directories alike, it's easy to accidentally make files executable or directories non-traversable. See our full guide to recursive chmod for how to apply different modes to files and directories in one pass.

FAQ

What does chmod 755 mean?

It gives the owner full access (read, write, execute) and gives group and others read and execute but not write — rwxr-xr-x. It's the standard mode for directories and executables that everyone should be able to use but only the owner should change.

What does chmod 644 mean?

The owner can read and write the file; group and others can only read it — rw-r--r--. It's the typical mode for regular files like configs or static assets that don't need to be executed.

How are chmod numbers calculated?

Each permission has a fixed value — read is 4, write is 2, execute is 1 — and you add the values you want for a class together. Read and execute is 4+1=5; read, write, and execute is 4+2+1=7. Do that once each for owner, group, and others to get the three-digit mode.

What's the difference between 755 and 775?

755 gives only the owner write access; group and others can read and execute but not modify. 775 extends write access to the group as well, which is useful when multiple users in the same group need to edit shared files, but it also means anyone in that group can change or delete them.

Why is chmod 777 risky?

777 gives every user on the system — not just an intended group — full read, write, and execute access. On a shared or internet-facing server, that means any user or compromised process can modify or replace the file. It's rarely the actual fix for a permissions error; the real fix is usually correcting ownership or granting access to the specific group that needs it.