systemd: Set up chroot environment in a separate service, once.

src/debian/aprsc-chroot.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=APRS-IS server chroot environment
+After=network.target
+Documentation=http://he.fi/aprsc/, man:aprsc(8)
+
+[Service]
+Type=oneshot
+ExecStart=/opt/aprsc/sbin/aprsc-prepare-chroot.sh
+User=root
+Group=root
+
+[Install]
+WantedBy=multi-user.target
+Alias=aprsc-chroot.service

src/debian/aprsc.service

@@ -1,11 +1,11 @@
 [Unit]
 Description=APRS-IS server
-After=network.target
+After=network.target aprsc-chroot.service
+Requires=aprsc-chroot.service
 Documentation=http://he.fi/aprsc/, man:aprsc(8)
 
 [Service]
 Type=simple
-ExecStartPre=/opt/aprsc/sbin/aprsc-prepare-chroot.sh
 ExecStart=/opt/aprsc/sbin/aprsc -u aprsc -t /opt/aprsc -e info -o file -r logs -c etc/aprsc.conf
 ExecReload=/bin/kill -USR1 $MAINPID
 PIDFile=/opt/aprsc/logs/aprsc.pid

src/debian/aprsc@.service

@@ -1,11 +1,11 @@
 [Unit]
 Description="APRS-IS server #%i"
-After=network.target
+After=network.target aprsc-chroot.service
+Requires=aprsc-chroot.service
 Documentation=http://he.fi/aprsc/, man:aprsc(8)
 
 [Service]
 Type=simple
-ExecStartPre=/opt/aprsc/sbin/aprsc-prepare-chroot.sh
 ExecStart=/opt/aprsc/sbin/aprsc -n aprsc-%i -u aprsc -t /opt/aprsc -e info -o file -r logs -c etc/aprsc-%i.conf
 ExecReload=/bin/kill -USR1 $MAINPID
 PIDFile=/opt/aprsc/logs/aprsc-%i.pid

src/debian/rules

@@ -78,6 +78,7 @@ binary-arch: build install
 	# this will work on ubuntu 18.04: dh_installsystemd
 	# but in the mean time:
 	cp -p $(CURDIR)/debian/aprsc@.service $(CURDIR)/debian/aprsc/lib/systemd/system/aprsc@.service
+	cp -p $(CURDIR)/debian/aprsc-chroot.service $(CURDIR)/debian/aprsc/lib/systemd/system/aprsc-chroot.service
 #	dh_installcron
 #	dh_installinfo
 	dh_installman