After a recent Owncloud 8.o.x update I started getting this error being logged whenever the owncloud cron job run. To resolve the issue I had to change the cron job to be run as the user apache.
The webserver on CentOS is run under the user apache, on other linux flavous it’s www-data to find out what it is on your system just check the error being logged it will log the user running the webserver.
Current user: someuser
Web server user: apache <- This is the user you want.