if1sec: fixes

plugins/network/if1sec_

@@ -7,8 +7,15 @@ cache="$MUNIN_PLUGSTATE/munin.$plugin.value"
 
 IFACE="${0##*/if1sec_}"         # interface
 
+if [ ! -r "/sys/class/net/$IFACE/statistics/tx_bytes" ]
+then
+	echo "# Unknown Interface : $IFACE"
+	exit 1
+fi
+
 if [ "$1" = "acquire" ]
 then
+        (
                 while sleep 1
                 do
                         echo $(
@@ -19,7 +26,8 @@ then
                 done | awk "{
                                 print \"${IFACE}_tx.value \" \$1 \":\" \$2;
                                 print \"${IFACE}_rx.value \" \$1 \":\" \$3;
-		}" >> $cache &
+                        }" >> $cache
+        ) &
         echo $! > $pidfile
         exit 0
 fi
@@ -32,13 +40,16 @@ graph_title Interface 1sec stats for ${IFACE}
 graph_category 1sec::network
 graph_data_size custom 1d, 10s for 1w, 1m for 1t, 5m for 1y
 update_rate 1
+${IFACE}_tx.type DERIVE
+${IFACE}_tx.min 0
+${IFACE}_rx.type DERIVE
+${IFACE}_rx.min 0
 EOF
         exit 0
 fi
 
 # values
-cat ${FILE_VALUES}
-> ${FILE_VALUES}
+cat ${cache}
+> ${cache}
 
 exit 0
-