Your webserver user doesn’t have the permission to create new files in /var/log. For apache and other processes the log rotation is done by a system cronjob. You have two options:
- Let the system-cronjob also do the rotation of your owncloud.log. Create a new file
/etc/logrotate.d(check the man pages of logrotate about all the options):
/var/log/owncloud.log {
daily
missingok
rotate 14
compress
delaycompress
notifempty
create 640 root adm
} - Put your owncloud-logfiles in a location where
www-datahas the permission to write, e.g. /var/log/owncloud