Couple of debian fixes, cannot use variable expansions this way

README.md

@@ -32,11 +32,11 @@ sudo systemctl start bird-exporter
 
 Default configuration:
 ```
-BIRD_RUN_USER=bird
+BIRD_EXPORTER_ARGS="-web.listen-address=:9324 -period=60s -bird.socket=/var/run/bird/bird.ctl"
-BIRD_RUN_GROUP=bird
-BIRD_EXPORTER_ARGS="-period=60s -bird.socket=/var/run/bird/bird.ctl"
 ```
 
+The service runs as the `bird` user and group.
+
 ## Documentation
 
 - **Manual page**: `man bird-exporter` (after package installation)

debian/bird-exporter.default

@@ -1,8 +1,3 @@
 # Default settings for bird-exporter
-
-# User and group to run bird-exporter as
-BIRD_RUN_USER=bird
-BIRD_RUN_GROUP=bird
-
 # Command line arguments to pass to bird-exporter
-BIRD_EXPORTER_ARGS="-period=60s -bird.socket=/var/run/bird/bird.ctl"
+BIRD_EXPORTER_ARGS="-web.listen-address=:9324 -period=60s -bird.socket=/var/run/bird/bird.ctl"

debian/bird-exporter.postinst

@@ -0,0 +1,18 @@
+#!/bin/sh
+set -e
+
+case "$1" in
+    configure)
+        # Create bird user if it doesn't exist
+        if ! getent passwd bird > /dev/null; then
+            adduser --system --group --no-create-home \
+                --home /nonexistent \
+                --gecos "BIRD routing daemon" \
+                bird
+        fi
+        ;;
+esac
+
+#DEBHELPER#
+
+exit 0

debian/bird-exporter.service

@@ -6,9 +6,9 @@ Wants=bird.service
 
 [Service]
 Type=simple
+User=bird
+Group=bird
 EnvironmentFile=-/etc/default/bird-exporter
-User=${BIRD_RUN_USER:-bird}
-Group=${BIRD_RUN_GROUP:-bird}
 ExecStart=/usr/bin/bird-exporter $BIRD_EXPORTER_ARGS
 Restart=always
 RestartSec=5

debian/rules

@@ -14,7 +14,6 @@ override_dh_auto_build:
 
 override_dh_auto_install:
 	install -D -m 0755 bird-exporter debian/bird-exporter/usr/bin/bird-exporter
-	install -D -m 0644 debian/bird-exporter.service debian/bird-exporter/lib/systemd/system/bird-exporter.service
 	install -D -m 0644 debian/bird-exporter.default debian/bird-exporter/etc/default/bird-exporter
 	install -D -m 0644 docs/bird-exporter.1 debian/bird-exporter/usr/share/man/man1/bird-exporter.1