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Chmod Calculator

Visual permissions generator for Linux/Unix files. Convert between numeric (octal) and symbolic formats.

Scope
Read (4)
Write (2)
Execute (1)
Owner
Group
Public
Type:

Linux Permissions (Octal)

e.g. 755

Symbolic Notation

e.g. -rwxr-xr-x

Command

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Understanding Linux Permissions

Linux and Unix-like operating systems use a permissions system to control access to files and directories. These can be represented numerically (octal) or symbolically.

Owner

The user who owns the file. Usually the creator. Permissions here apply only to this specific user.

Group

A defined group of users. Any user in this group will have these permissions, unless they are the owner.

Public / Other

Everyone else. Be careful with write permissions here, as it allows anyone on the system to modify the file.

Common Permission Presets

  • 777 (rwxrwxrwx) Full access for everyone (Insecure)
  • 755 (rwxr-xr-x) Owner full, others read/execute (Web Standard)
  • 644 (rw-r--r--) Owner read/write, others read only (Files)
  • 600 (rw-------) Private to owner only (Keys/Secrets)

Frequently Asked Questions

The numbers are a sum of permissions: Read = 4, Write = 2, Execute = 1.
Example: Read + Write = 4 + 2 = 6.
Read + Execute = 4 + 1 = 5.
`chmod +x` adds the executable permission to the file for all users (Owner, Group, and Other), making a script runnable.
For folders, **755** (drwxr-xr-x) is standard. For files, **644** (-rw-r--r--) is recommended. This allows only the owner specifically to write, while others can only read.
Use the -R flag. For example, chmod -R 755 /path/to/directory will apply the permissions to the directory and everyone file/folder inside it.
chmod changes who can do what (permissions), while chown changes who owns the file (ownership). You often need to use both.
This is symbolic mode. u stands for User (Owner), + means add permission, and x means Execute. So it adds execute permission for the owner.
You only have permission to change files you own. If you don't own the file, you must use sudo before your command to run it as root (e.g., sudo chmod 755 file).

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