[rrd-users] --logarithmic & negative values

Jan Kontze kontze at ub.fu-berlin.de
Tue Dec 14 18:14:34 MET 2004

Hi Guys!

I used to have my network loads plotted over and under zero - the incoming
traffic shown over the zero line and the outgoing traffice "mirrored"
under the zero (faked as negative values).

Because of huge fluctuations of network traffic there are some peaks which
effectivly prevent from one being able to distinguish measured traffic
amount in times without high traffic.

Therefore I ogled with the --logarithmic option of rrdtool.  
Unfortunately logarithms don't like negative numbers <g> (as I faked it for
my outgoing traffic) and that's why(?) using the --logarithmic in rrdtool
frees me from the the negative values and only the incoming traffic is
display by rrdtool yet (as it's positive).

Do you have any idea how I could keep the idea of incoming traffic
displayed (corrrectly!) over a line (the zero line), the outgoing network
traffic shown below the zero line and have nevertheless a logarithmic

Any hints appreciated!!

Here is how I create my network load graph:

  $rrdtool graph \
    "$2" -i -a GIF \
    -t "$5 -- ${cfpr}Traffic auf $ifname ($tstr)" \
    -s -$4 \
    -e $($date -d "$step seconds ago" +%s) \
    -w $picy -h $picx \
    -v "Bytes/s" \
    --lazy \
    DEF:in=${db}:in:AVERAGE \
    DEF:out=${db}:out:AVERAGE \
    "CDEF:unknown_in=in,UN,INF,UNKN,IF" \
    "AREA:unknown_in#d0d0d0" \
    "CDEF:out_neg=out,-1,*" \
    "CDEF:unknown_out=out,UN,INF,UNKN,IF" \
    "CDEF:unknown_out_neg=unknown_out,-1,*" \
    "AREA:unknown_out_neg#d0d0d0" \
    "AREA:in#32CD32:Incoming" \
    "LINE1:in#336600" \
    "GPRINT:in:MAX:  Max\\: %5.1lf %s" \
    "GPRINT:in:AVERAGE: Avg\\: %5.1lf %S" \
    "GPRINT:in:LAST: Current\\: %5.1lf %SBytes/sec\\n" \
    "AREA:out_neg#4169E1:Outgoing" \
    "LINE1:out_neg#0033CC" \
    "GPRINT:out:MAX:  Max\\: %5.1lf %S" \
    "GPRINT:out:AVERAGE: Avg\\: %5.1lf %S" \
    "GPRINT:out:LAST: Current\\: %5.1lf %SBytes/sec\n" \
    --base=1000 \
    "COMMENT:\s" \
    "COMMENT:\s" \
    "COMMENT:Generated on $($date)\c" \
    HRULE:0#000000  VRULE:$($date -d "$($date +%m/%d/%y) 00:00" "+%s")#ff0000

Thanx & Bye!
Jan Kontze
		It's bad luck to be superstitious
				-- Andrew W. Mathis

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