Init script may not be properly cleaning up pid file.
The issue seems to be that the PPA init script is not properly handing a stale PID file? The Systemd unit file takes care of this.
Updated by Peter Manev almost 3 years ago
It is fixed in one of the test repos here - https://launchpad.net/~oisf/+archive/ubuntu/suricata-ids-ips/+packages (you can just do "add-apt-repository ppa:oisf/suricata-ids-ips ; apt-get update" to try it)