diff -upr Shorewall-init.orig/configure Shorewall-init/configure
--- Shorewall-init.orig/configure	2020-09-25 01:02:16.000000000 +0300
+++ Shorewall-init/configure	2024-02-01 06:27:06.653348848 +0200
@@ -134,7 +134,7 @@ if [ -z "$vendor" ]; then
 	*)
 	    if [ -f /etc/debian_version ]; then
 		params[HOST]=debian
-		ls -l /sbin/init | fgrep -q systemd &&  rcfile=shorewallrc.debian.systemd || rcfile=shorewallrc.debian.sysvinit
+		ls -l /sbin/init | grep -F -q systemd &&  rcfile=shorewallrc.debian.systemd || rcfile=shorewallrc.debian.sysvinit
 	    elif [ -f /etc/altlinux-release ] ; then
 		params[HOST]=alt
 	    elif [ -f /etc/redhat-release ]; then
@@ -163,7 +163,7 @@ else
     if [ $vendor = linux ]; then
 	rcfile=shorewallrc.default;
     elif [ $vendor = debian -a -f /etc/debian_version ]; then
-	ls -l /sbin/init | fgrep -q systemd && rcfile=shorewallrc.debian.systemd || rcfile=shorewallrc.debian.sysvinit
+	ls -l /sbin/init | grep -F -q systemd && rcfile=shorewallrc.debian.systemd || rcfile=shorewallrc.debian.sysvinit
     else
 	rcfile=shorewallrc.$vendor
     fi