Chmod Calculator

What Is chmod?

chmod (change mode) is a Unix and Linux command used to set file and directory permissions. It controls who can read, write, or execute a file. Permissions are assigned to three categories: the file owner, the group, and all other users.

Understanding Permission Values

Each permission type has a numeric value: read (4), write (2), and execute (1). These values are summed for each category to produce a single digit. Three digits together form the complete permission code:

7 = read (4) + write (2) + execute (1) = rwx
6 = read (4) + write (2)               = rw-
5 = read (4) + execute (1)             = r-x
4 = read (4)                           = r--
0 = no permissions                     = ---

Common Permission Examples

• 755 — Owner can read, write, and execute. Group and others can read and execute. Common for scripts and directories.
• 644 — Owner can read and write. Group and others can only read. Standard for regular files.
• 700 — Owner has full access. No one else can access the file. Used for private scripts.
• 600 — Owner can read and write. No access for anyone else. Common for SSH keys and config files.
• 444 — Everyone can read, no one can write or execute. Read-only for all users.
• 777 — Full access for everyone. Generally discouraged for security reasons.

Numeric vs Symbolic Notation

Permissions can be expressed in two ways. Numeric (octal) notation uses three digits like 755. Symbolic notation uses letters: r for read, w for write, and x for execute. A dash (-) indicates the permission is not set. For example, rwxr-xr-x is the symbolic form of 755.

How to Use This Calculator

1. Toggle checkboxes in the permission grid to set read, write, and execute for each user category.
2. Enter a numeric value directly (like 755) and the checkboxes will update automatically.
3. Use a preset for common permission patterns like 644, 755, or 777.
4. Copy the result — numeric code, symbolic string, or the full chmod command — with one click.