Fis systemd support on debian system version 13 (trixie) or newer.

install_opendmarc.sh

@@ -116,9 +116,11 @@ echo_skipped() {
 
 # - Is 'systemd' supported on this system
 # -
-if [ "X`which systemd`" = "X" ]; then
-   SYSTEMD_EXISTS=false
-else
+SYSTEMD_EXISTS=false
+systemd=$(which systemd)
+systemctl=$(which systemctl)
+
+if [[ -n "$systemd" ]] || [[ -n "$systemctl" ]] ; then
    SYSTEMD_EXISTS=true
 fi