Mysql/Maria problem

Hello world!
I have a big problem with mysql/maria installation

First, i install package, all OK :
# apk add mysql mysql-client

Next, i type this command :
# /usr/bin/mysql_install_db --user=mysql
and i have this error :
150926 15:29:22 [ERROR] mysqld: File './mysql-bin.index' not found (Errcode: 13)
150926 15:29:22 [ERROR] Aborting

And then, i start maria :
# service mariadb start
but :
* Caching service dependencies ... [ ok ]
* Starting mysqld ...
* start-stop-daemon: caught an interrupt
* start-stop-daemon: /usr/bin/mysqld_safe died [ ! ! ]
* ERROR: mariadb failed to start

Please, help me.