MySQL 5.7 Release Notes
MySQL client programs prompt for a password when invoked with
a --password or
-p option that has no following password
value:
$> mysql -u user_name -p
Enter password:
On some systems, you may find that your password works when
specified in an option file or on the command line, but not
when you enter it interactively at the Enter
password: prompt. This occurs when the library
provided by the system to read passwords limits password
values to a small number of characters (typically eight). That
is a problem with the system library, not with MySQL. To work
around it, change your MySQL password to a value that is eight
or fewer characters long, or put your password in an option
file.