I had this issue as well. Fixed it with paulschulz's suggestion of adding the "-pf /run/dhcp-server/dhcpd.pid" command line option into /etc/init/isc-dhcp-server.conf.
I had this issue as well. Fixed it with paulschulz's suggestion of adding the "-pf /run/dhcp- server/ dhcpd.pid" command line option into /etc/init/ isc-dhcp- server. conf.