On Ubuntu 16.04.2 I noticed that systemd is in degraded state (systemctl status) after some uptime or after wake from suspend, because dns-clean.service failed.
dns-clean.service has ExecStartPre=/bin/mkdir /var/run/pppconfig
When I remove /var/run/pppconfig directory which is empty, the service can be started successfully (systemctl start dns-clean.service) and systemd is in running mode.
The directory /var/run/pppconfig is not supposed to exist when the system wants to start the service, so why is it still here ?
There is a Debian bug report about this: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826040