--- opendmarc.service.orig      2017-01-07 16:36:04.000000000 +0000
+++ opendmarc.service   2017-01-18 12:18:41.340308427 +0000
@@ -8,3 +8,9 @@
-PIDFile=/var/run/opendmarc/opendmarc.pid
-User=opendmarc
-ExecStart=/usr/sbin/opendmarc -p local:/var/run/opendmarc/opendmarc.sock  -u opendmarc -P /var/run/opendmarc/opendmarc.pid
+# pickup any 'Socket' setting in opendmarc.conf, default local:/var/run/opendmarc/opendmarc.sock, and set defaults for PIDFILE USER GROUP
+Environment=SOCKET=$(echo Socket local:/var/run/opendmarc/opendmarc.sock|cat /etc/opendmarc.conf -|grep -m1 ^Socket|cut -d ' ' -f2-) PIDFILE=/var/run/opendmarc/opendmarc.pid USER=opendmarc GROUP=opendmarc
+# settings in /etc/default/opendmarc (if any) take precedence
+EnvironmentFile=-/etc/default/opendmarc
+PIDFile=$PIDFILE
+User=$USER
+Group=$GROUP
+ExecStart=/usr/sbin/opendmarc -p $SOCKET  -u opendmarc -P $PIDFILE $DAEMON_OPTS