improvement: check if lqos_node_manager exists in build_dpkg.sh

src/build_dpkg.sh

@@ -69,9 +69,20 @@ sudo python3 -m pip install --root-user-action=ignore --quiet --break-system-pac
 cp /opt/libreqos/src/bin/lqosd.service.example /etc/systemd/system/lqosd.service
 cp /opt/libreqos/src/bin/lqos_scheduler.service.example /etc/systemd/system/lqos_scheduler.service
 
-/bin/systemctl stop lqos_node_manager # In case it's running from a previous release
-/bin/systemctl disable lqos_node_manager # In case it's running from a previous release
-rm -f /etc/systemd/system/lqosd_node_manager.service # In case it's running from a previous release
+service_exists() {
+    local n=$1
+    if [[ $(systemctl list-units --all -t service --full --no-legend "$n.service" | sed 's/^\s*//g' | cut -f1 -d' ') == $n.service ]]; then
+        return 0
+    else
+        return 1
+    fi
+}
+
+if service_exists lqos_node_manager; then
+    /bin/systemctl stop lqos_node_manager # In case it's running from a previous release
+    /bin/systemctl disable lqos_node_manager # In case it's running from a previous release
+    rm -f /etc/systemd/system/lqosd_node_manager.service # In case it's running from a previous release
+fi
 
 /bin/systemctl daemon-reload
 /bin/systemctl enable lqosd lqos_scheduler