Configuration - Ubuntu 16.04 server - DRBD 8.4.5 - Ispconfig 3.1.9 - 2 servers in cluster When I try to restart master server it hangs during a process (found in syslog) block drbd2: State change failed: Device is held open by someone Exactly the same behavior when I manually try to transfer resources to secondary server. Since this volume contains only websites (mounts to /var/www), I started to suspect apache. With a help of "lsof" I found out, that a process apache2 keeps open a few hundred files "error.log", which obviously prevent drbd from unmounting a volume. apache2 18473 www-data 50w REG 147,2 1477810 22151702 /var/www/clients/client25/web20/log/error.log Approx half of these files are zero size. Question - am I looking in the right direction at all ? - if yes, how to force apache not to keep these files open at all times ?