Permissions. Every file, folder, and app stored on your Mac has permission settings, which determine which user accounts can read, write to, or run the file, folder, or app. These permissions include POSIX permissions and Access Control Lists (ACLs). To make a user’s POSIX permissions more restrictive or less restrictive, you can adjust their umask value.

Umasks. A three-digit number can represent the POSIX permissions for a file. You might see permissions represented this way when you view them from Terminal. Each digit is between 0 and 7. When you create a file, the umask value is subtracted from a default value (usually 666 for files and 777 for folders) to determine the permissions for the new file or folder. For example, a default umask of 022 sets permissions of 644 on new files and 755 on new folders.