[mrtg] Problem with Negative Numbers

Steve Swords steve at unwiredbb.com
Wed Apr 18 18:39:03 CEST 2007

```I multiply the target by -1 to graph RSSI on our Trango gear. Keeps the same
number and makes it positive for graphing....

Steve Swords
<http://www.unwiredbb.com/> http://www.unwiredbb.com
steve at unwiredbb.com
364 W. Fallbrook Ste. 102
Fresno, Ca 93711
(559) 261-4444 ext 502
(559) 261-4445 (Fax)

_____

From: mrtg-bounces at lists.oetiker.ch [mailto:mrtg-bounces at lists.oetiker.ch]
On Behalf Of Craig Metzer
Sent: Wednesday, April 18, 2007 8:53 AM
To: mrtg at lists.oetiker.ch
Subject: [mrtg] Problem with Negative Numbers

Im trying to poll a satellite modem for Rx Signal Level.  The modem returns
a negative integer ten times the level (ex. -575 indicates the level is
-57.5 dBm).  Ive configured a conversion function so I can log the value
returned by snmpget and compare it to the value in the log file.  It appears
that MRTG is not recognizing the number as negative.  It appears it is not
recognizing the binary 1 MSD as a negative sign.

===========

Config file:

ConversionCode: functs.pl

Target[my-pub-sat-01-rsl]:
.1.3.6.1.4.1.6247.28.1.3.3.4.0&.1.3.6.1.4.1.6247.28.1.3.3.4.0:myROcs at my-pub-
sat-01.domain.gov|neg_int

==========

Functs.pl:

sub neg_int {

my \$n = shift;

open FH, ">> rx_lvl.log";

#    my \$o = (2^31 - \$n) / 10;

my \$o = \$n / 10;

print FH localtime(time) . " -> IN: \$n\tOUT: \$o\n";

close FH;

return \$o;

}

===========

Logs:

1176910486 2147483590 2147483590

1176910486 0 0 0 0

1176910186 0 0 0 0

1176909900 0 0 0 0

1176909600 0 0 0 0

1176909300 0 0 0 0

1176909000 0 0 0 0

\$ cat rx_lvl.log

Wed Apr 18 16:29:46 2007 -> IN: -578    OUT: -57.8

Wed Apr 18 16:29:46 2007 -> IN: -578    OUT: -57.8

Wed Apr 18 16:34:46 2007 -> IN: -578    OUT: -57.8

Wed Apr 18 16:34:46 2007 -> IN: -578    OUT: -57.8

_____

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