By default, the passwd command assumes a minimum length of six characters. You can use the PASSLENGTH default in the /etc/defaults/passwd files to change that by setting the minimum number of characters that a user's password must contain to some other number.
To set the minimum number of characters to something other than six, type the appropriate number of characters after the equal sign in the PASSLENGTH= line:
Where N is the number of characters. For example, PASSLENGTH=7.