diff --git a/backend/cron-dl-robust.sh b/backend/cron-dl-robust.sh
new file mode 100755
index 0000000..074a5a3
--- /dev/null
+++ b/backend/cron-dl-robust.sh
@@ -0,0 +1,81 @@
+#! /bin/bash
+
+USER=live
+
+SOURCE=https://download.openstreetmap.fr/replication/planet/minute/
+SOURCE2=https://planet.openstreetmap.org/replication/minute/
+SWITCH=0
+
+LOCK_FILE=/run/lock/$USER-crontab-backend
+
+DELAY=10
+
+exec 200>"$LOCK_FILE"
+flock -n 200
+RC=$?
+if [ "$RC" != 0 ]; then
+    echo "ERROR: Already running script. Try again after sometime"
+    exit 1
+fi
+
+if [ -e /data/work/$USER/prev-seq ]; then
+  PREV_SEQ="$(cat /data/work/$USER/prev-seq)"
+  if [ $PREV_SEQ  -ge 0 ] 2>/dev/null; then
+    echo "DEBUG: PREV_SEQ est numerique"
+  else
+    echo "ERROR: PREV_SEQ n est pas numerique. rm /data/work/$USER/prev-seq et init PREV_SEQ=0"
+    echo "ERROR: PREV_SEQ n est pas numerique. rm /data/work/$USER/prev-seq et init PREV_SEQ=0" >&2
+    rm -f /data/work/$USER/prev-seq
+    PREV_SEQ=0
+  fi
+else
+  echo "WARN: fichier /data/work/$USER/prev-seq absent. init PREV_SEQ=0"
+  PREV_SEQ=0
+fi
+echo "DEBUG: PREV_SEQ $PREV_SEQ"
+
+[ $(date +%S) -le 10 ] && echo "DEBUG: trop proche de la minute ronde. attente de quelques secondes" && sleep 12
+echo "DEBUG: wget -4 --no-check-certificate -o /dev/null -O /dev/stdout $SOURCE/state.txt|grep sequenceNumber|cut -d '=' -f 2"
+SEQ=`wget -4 --no-check-certificate -o /dev/null -O /dev/stdout $SOURCE/state.txt|grep sequenceNumber|cut -d '=' -f 2`
+
+if [ $SEQ  -ge 0 ] 2>/dev/null; then
+  echo "DEBUG: SEQ est numerique"
+else
+  echo "ERROR: SEQ n est pas numerique"
+  echo "ERROR: SEQ n est pas numerique" >&2
+  exit 2
+fi
+
+if (( SEQ <= PREV_SEQ-DELAY )); then
+  echo "WARNING: downloaded SEQ $SEQ <= PREV_SEQ $PREV_SEQ"
+  echo "INFO: Switch to $SOURCE2"
+  SEQ=`wget -4 --no-check-certificate -o /dev/null -O /dev/stdout $SOURCE2/state.txt|grep sequenceNumber|cut -d '=' -f 2`
+  SWITCH=1
+fi
+echo "DEBUG: downloaded SEQ $SEQ"
+
+echo "INFO: PREV_SEQ $PREV_SEQ SEQ $SEQ"
+
+MM=$[$SEQ/1000000]
+KK=$[$SEQ-$MM*1000000]
+KK=$[$KK/1000]
+UU=$[$SEQ-$MM*1000000-$KK*1000]
+A=`printf %03d $MM`
+B=`printf %03d $KK`
+C=`printf %03d $UU`
+
+echo "DEBUG: $SEQ mean $A/$B/$C"
+if [ "$SWITCH" = 1 ]; then
+  echo "$SOURCE2/$A/$B/$C.osc.gz"
+  wget -4 --no-check-certificate -o /dev/null -O /dev/stdout $SOURCE2/$A/$B/$C.osc.gz|gunzip -c|chronic python3 compute-changeset-data.py
+  return_code="${?}"
+  echo "DEBUG: return_code $return_code"
+else
+  echo "$SOURCE/$A/$B/$C.osc.gz"
+  wget -4 --no-check-certificate -o /dev/null -O /dev/stdout $SOURCE/$A/$B/$C.osc.gz|gunzip -c|chronic python3 compute-changeset-data.py
+  return_code="${?}"
+  echo "DEBUG: return_code $return_code"
+fi
+
+echo $SEQ > /data/work/$USER/prev-seq
+exit $return_code