Use a helper to start dump1090-fa so we can read ENABLED from the defaults file, like beast-splitter does

debian/dump1090-fa.default

@@ -1,11 +1,14 @@
 # dump1090-fa configuration
-# This is read by the systemd service file as an environment file,
-# and evaluated by some scripts as a POSIX shell fragment.
+# This is sourced by /usr/share/dump1090-fa/start-dump1090-fa as a
+# shellscript fragment.
 
 # If you are using a PiAware sdcard image, this config file is regenerated
 # on boot based on the contents of piaware-config.txt; any changes made to this
 # file will be lost.
 
+# dump1090-fa won't automatically start unless ENABLED=yes
+ENABLED=yes
+
 RECEIVER_OPTIONS="--device-index 0 --gain -10 --ppm 0 --net-bo-port 30005"
 DECODER_OPTIONS="--max-range 360"
 NET_OPTIONS="--net --net-heartbeat 60 --net-ro-size 1000 --net-ro-interval 1 --net-ri-port 0 --net-ro-port 30002 --net-sbs-port 30003 --net-bi-port 30004,30104 --net-bo-port 30005"

debian/dump1090-fa.install

@@ -1,3 +1,4 @@
 public_html/* usr/share/dump1090-fa/html
 debian/lighttpd/* etc/lighttpd/conf-available
-bladerf/* /usr/share/dump1090-fa/bladerf
+bladerf/* usr/share/dump1090-fa/bladerf
+debian/start-dump1090-fa usr/share/dump1090-fa/

debian/dump1090-fa.service

@@ -7,17 +7,14 @@ Wants=network.target
 After=network.target
 
 [Service]
-EnvironmentFile=/etc/default/dump1090-fa
-EnvironmentFile=-/var/cache/piaware/location.env
 User=dump1090
 RuntimeDirectory=dump1090-fa
 RuntimeDirectoryMode=0755
-ExecStart=/usr/bin/dump1090-fa \
- $RECEIVER_OPTIONS $DECODER_OPTIONS $NET_OPTIONS $JSON_OPTIONS $PIAWARE_DUMP1090_LOCATION_OPTIONS \
- --write-json /run/dump1090-fa --quiet
+ExecStart=/usr/share/dump1090-fa/start-dump1090-fa --write-json /run/dump1090-fa --quiet
 Type=simple
 Restart=on-failure
 RestartSec=30
+RestartPreventExitStatus=64
 Nice=-5
 
 [Install]

debian/start-dump1090-fa

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+# Helper script that reads /etc/default/dump1090-fa
+# and either starts dump1090-fa with the configured
+# arguments, or exits with status 64 to tell systemd
+# not to auto-restart the service.
+
+if [ -f /etc/default/dump1090-fa ]
+then
+    . /etc/default/dump1090-fa
+fi
+
+if [ -f /var/cache/piaware/location.env ]
+then
+    . /var/cache/piaware/location.env
+fi
+
+if [ "x$ENABLED" != "xyes" ]
+then
+    echo "dump1090-fa not enabled in /etc/default/dump1090-fa" >&2
+    exit 64
+fi
+
+if [ -n "$LAT" -a -n "$LON" ]
+then
+    POSITION="--lat $LAT --lon $LON"
+fi
+
+exec /usr/bin/dump1090-fa \
+     $RECEIVER_OPTIONS $DECODER_OPTIONS $NET_OPTIONS $JSON_OPTIONS $POSITION \
+     "$@"
+# exec failed, do not restart
+exit 64