Found existing config file ./my.cnf on the system.

Because this file might be in use, it was not replaced,

but was used in bootstrap (unless you used --defaults-file)

and when you later start the server.

The new default config file was created as ./my-new.cnf

以上提示是在执行了

scripts/mysql_install_db --user=mysql

之后提示的。这是由于我的/usr/local/mysql/下已经有了my.cnf。将其改名，再重试，就ok了