[Dovecot] How to make Dovecot verbous

[Frank Walter]

Hello

I am struggling with Dovecot 2 (coming from Dovecot 1.0.10) with mysql Authentification for Postfix.
I get errors when using it:

dovecot: auth: Fatal: Unknown database driver 'mysql'
dovecot: master: Error: service(auth): command startup failed, throttling

But a first thing would be to log the real errors, if there are any, so I set in 

/etc/dovecot/conf.d/10-logging.conf

auth_verbose, auth_verbose_passwords, auth_debug, auth_debug_passwords, mail_debug, verbose_ssl 

all to yes and I set:

debug_log_path = /var/log/dovecot-debug.log

but there is no logfile after restarting dovecot.

How can I enable a (verbous) own Logfile in Dovecot?

frank