Warning: One can only use the --user switch if running as root

[David M.]

I started the mysql database with the "safe_mysql d" command and with
the user who own mysql.

in the errr-log file, I have that:

050123 23:16:50 mysqld started
Warning: One can only use the --user switch if running as root
/exlibris/sfx_ver/sfx_version_2/app/mysql/libexec/mysqld: ready for
connections

What is the meaning of

"Warning: One can only use the --user switch if running as root" ?

thanks !

David