the rpm postinstall script must call mysql_install_db with --user=mysql,
and mysql_install_db must then pass this to mysqld. Otherwise, mysqld
runs as root, and if you have --log-bin=somewhere_out_of_var_lib_mysql
it creates binlog files owned by root in this dir, and this dir is not
fixed by the 'chmod mysql', so files remain owned by root, and later mysqld
(running as 'mysql') can't read them.
I'm hardcoding 'mysql' in the postinstall script, but it's already hardcoded
there in many places (see the useradd and chown) so it's ok.