Umask Calculator

What is umask?

The umask (user file-creation mode mask) is a value that determines which permission bits are removed from newly created files and directories. It acts as a filter that strips away permissions you don't want granted by default.

Default Base Permissions

• Files: 666 (rw-rw-rw-) — read and write for all, no execute
• Directories: 777 (rwxrwxrwx) — read, write, and execute for all

Files don't get execute permission by default because it would be a security risk to make every new file executable.

The Calculation

The effective permissions are calculated with a bitwise AND-NOT operation:

effective = base AND (NOT umask)

Example with umask 022:
  Files:       666 AND (NOT 022) = 666 AND 755 = 644 (rw-r--r--)
  Directories: 777 AND (NOT 022) = 777 AND 755 = 755 (rwxr-xr-x)

Common Umask Values

• 022 — Default on most systems. Files: 644, Dirs: 755. Owner has full access, others can read
• 027 — Restrictive. Files: 640, Dirs: 750. Group can read, others have no access
• 077 — Private. Files: 600, Dirs: 700. Only owner has access
• 002 — Group-friendly. Files: 664, Dirs: 775. Group has same access as owner

Setting Umask Permanently

To persist your umask across sessions, add the umask command to your shell profile:

• Bash: ~/.bashrc or ~/.bash_profile
• Zsh: ~/.zshrc
• System-wide: /etc/profile or /etc/login.defs

Symbolic Notation

The umask -S command shows the umask in symbolic form, displaying the permissions that will be set (the inverse of what's masked). For example, umask 022 in symbolic form is u=rwx,g=rx,o=rx.

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