mxstartup: Run startstop commands as transient user services

mxstartup/mxservicectl

@@ -11,6 +11,26 @@ shopt -s nullglob
 # exit on any error
 set -e
 
+# Run "$@" as a user service of $MX_SRV_USER
+#
+function run_as_user_service() {
+    local uid cmd
+    uid=$(id -u "${MX_SRV_USER}") || return 1
+    printf -v cmd '%q ' "$@"
+    systemctl start user@$uid || return 1
+    su -l "${MX_SRV_USER}" -s /usr/bin/bash -c "XDG_RUNTIME_DIR=/run/user/$uid systemd-run --user --no-ask-password $cmd" || return 1
+}
+
+# Run "$@" as user $MX_SRV_USER
+# Attempt to run as a user service. If that fails, fall back to running it in the background
+#
+function run_as_user() {
+    run_as_user_service "$@" && return 0
+    local cmd
+    printf -v cmd '%q ' "$@"
+    su -l "${MX_SRV_USER}" -s /usr/bin/bash -c "$cmd" &
+}
+
 function mxsrv_start_one() {
    local cfg=$1
    local -i i mip mfwd
@@ -26,7 +46,7 @@ function mxsrv_start_one() {
            systemctl start "${MX_SRV_SCRIPT}" || true
            ;;
        *)
-           su - ${MX_SRV_USER} -c "${MX_SRV_SCRIPT} start" &
+           run_as_user ${MX_SRV_SCRIPT} start
            ;;
    esac
 
@@ -50,7 +70,7 @@ function mxsrv_stop_one() {
            systemctl stop "${MX_SRV_SCRIPT}" || true
            ;;
        *)
-           su - ${MX_SRV_USER} -c "${MX_SRV_SCRIPT} stop" &
+           run_as_user ${MX_SRV_SCRIPT} stop
            ;;
    esac