Auto-Archiving with cronjob generates empty logfile (no replies)

Hi,

i want to setup Auto-Archiving with a cronjob.

Our Piwik-Version: 2.8.3 with round about 200 domains.

Our cronjob :

56 * * * * /usr/local/bin/php5.4-cli /homepages/29/d104xxxxxxx/htdocs/DOMAIN/piwik/console core:archive --url=http://www.DOMAIN.de/piwik/ > /homepages/29/d104xxxxxxx/htdocs/DOMAIN/piwik/piwik-archive.log

The generated file piwik-archive.log is always empty (0 Byte). Same with test of the cron command: su -username ...

What can i do to get something written into the logfile? Or what can i do to get more information about what's missing?

Thanks!