What do the three octal digits mean?

Each digit is the permission for one class - owner, then group, then other - and is the sum of read (4), write (2), and execute (1). So 7 is read+write+execute, 5 is read+execute, 6 is read+write. That is why 755 means the owner can do everything and everyone else can read and execute, and 644 means the owner can read and write while others can only read.

What permissions should files and directories have?

A common safe default is 644 for files (owner read/write, others read) and 755 for directories (the execute bit on a directory means you can enter it). Secrets like private keys and .env files should be 600 - owner only. Avoid 777; world-writable files and directories are a real security risk and almost never necessary.

What is the execute bit on a directory?

On a file, execute means you can run it. On a directory, the execute bit means you can traverse into it and access files inside by name - so directories usually need execute wherever they need read. That is why directory permissions are typically 755 or 750 rather than 644.

Free tool · Runs in your browser

chmod calculator.

Tick read / write / execute for owner, group, and other to get the octal (like 755) and symbolic (rwxr-xr-x) permissions — or type an octal to see exactly what it allows. With the chmod command ready to copy.

Presets:

Or type octal:

Octal

000

Symbolic

---------

chmod 000 file

The permissions you set are the access you grant

File permissions are one of the oldest and most consequential controls on a server: they decide who can read a secret, overwrite a binary, or run a script. The octal shorthand is compact but easy to fat-finger — a stray digit turns a private key world-readable. Seeing the rwx grid, the octal, and the symbolic form line up at once makes the intent obvious before you run the command, and the common presets cover the cases you actually need.

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Who	Read (4)	Write (2)	Execute (1)
Owner
Group
Other