In Systemd, runlevel returns "unknown" and generate errors. Use strings (but do not detect if the system is booting)

check

@@ -18,12 +18,12 @@ fi
 
 RUNLEVEL=`runlevel | cut -f 2 -d ' '`
 [ "x$RUNLEVEL" == "x" ] && RUNLEVEL=0
-if [ $RUNLEVEL -eq 0 ] || [ $RUNLEVEL -eq 6 ]; then
+if [ "$RUNLEVEL" == "0" ] || [ "$RUNLEVEL" == "6" ]; then
   echo "Arret ou reboot en cours : on sort"
   exit
 fi
 
-if [ $RUNLEVEL -eq 1 ]; then
+if [ "$RUNLEVEL" == "1" ]; then
   echo "Démarrage en cours : on sort"
   exit
 fi