


 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



 NNNNAAAAMMMMEEEE
      rrdtutorial - Alex van den Bogaerdt's RRDtool tutorial

 DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
      RRDtool is written by Tobias Oetiker <oetiker@ee.ethz.ch> with
      contributions from many people all around the world. This document is
      written by Alex van den Bogaerdt <alex@ergens.op.het.net> to help you
      understand what RRDtool is and what it can do for you.

      The documentation provided with RRDtool can be too technical for some
      people. This tutorial is here to help you understand the basics of
      RRDtool. It should prepare you to read the documentation yourself.  It
      also explains the general things about statistics with a focus on
      networking.

 TTTTUUUUTTTTOOOORRRRIIIIAAAALLLL
      IIIImmmmppppoooorrrrttttaaaannnntttt

      Please don't skip ahead in this document!  The first part of this
      document explains the basics and may be boring.  But if you don't
      understand the basics, the examples will not be as meaningful to you.

      WWWWhhhhaaaatttt iiiissss RRRRRRRRDDDDttttoooooooollll ????

      RRDtool refers to Round Robin Database tool.  Round robin is a
      technique that works with a fixed amount of data, and a pointer to the
      current element. Think of a circle with some dots plotted on the edge,
      these dots are the places where data can be stored. Draw an arrow from
      the center of the circle to one of the dots, this is the pointer.
      When the current data is read or written, the pointer moves to the
      next element. As we are on a circle there is no beginning nor an end,
      you can go on and on. After a while, all the available places will be
      used and the process automatically reuses old locations. This way, the
      database will not grow in size and therefore requires no mainenance.
      RRDtool works with with Round Robin Databases (RRDs). It stores and
      retrieves data from them.

      WWWWhhhhaaaatttt ddddaaaattttaaaa ccccaaaannnn bbbbeeee ppppuuuutttt iiiinnnnttttoooo aaaannnn RRRRDDDDDDDD ????

      You name it, it will probably fit. You should be able to measure some
      value at several points in time and provide this information to
      RRDtool. If you can do this, RRDtool will be able to store it. The
      values need to be numerical but don't have to be, as opposed to MRTG,
      integers.

      Many examples talk about SNMP which is an acronym for Simple Network
      Management Protocol. "Simple" refers to the protocol -- it does not
      mean it is simple to manage or monitor a network. After working your
      way through this document, you should know enough to be able to
      understand what people are talking about. For now, just realize that



                                    - 1 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      SNMP is a way to ask devices for the values of counters they keep.  It
      is the value from those counters that are kept in the RRD.

      WWWWhhhhaaaatttt ccccaaaannnn IIII ddddoooo wwwwiiiitttthhhh tttthhhhiiiissss ttttoooooooollll ????

      RRDtool originated from MRTG (Multi Router Traffic Grapher).  MRTG
      started as a tiny little script for graphing the use of a connection
      to the Internet. MRTG evolved into a tool for graphing other data
      sources including temperature, speed, voltage, number of printouts and
      the like. Most likely you will start to use the RRDtool to store and
      process data collected via SNMP. The data will most likely be bytes
      (or bits) transfered from and to a network or a computer.  RRDtool
      lets you create a database, store data in it, retrieve that data and
      create graphs in GIF format for display on a web browser. Those GIF
      images are dependent on the data you collected and could be, for
      instance, an overview of the average network usage, or the peaks that
      occurred.  It can also be used to display tidal waves, solar
      radiation, power consumption, number of visitors at an exhibition,
      noise levels near an airport, temperature on your favorite holiday
      location, temperature in the fridge and whatever you imagination can
      come up with. You need a sensor to measure the data and be able to
      feed the numbers to RRDtool.

      WWWWhhhhaaaatttt iiiiffff IIII ssssttttiiiillllllll hhhhaaaavvvveeee pppprrrroooobbbblllleeeemmmmssss aaaafffftttteeeerrrr rrrreeeeaaaaddddiiiinnnngggg tttthhhhiiiissss ddddooooccccuuuummmmeeeennnntttt ????

      First of all: read it again! You may have missed something.  If you
      are unable to compile the sources and you have a fairly common OS, it
      will probably not be the fault of RRDtool. There may be precompiled
      versions around on the Internet. If they come from trusted sources,
      get one of those.  If on the other hand the program works but does not
      give you the expected results, it will be a problem with configuring
      it. Review your configuration and compare it with the examples that
      follow.

      There is a mailing list and an archive of it. Read the list for a few
      weeks and search the archive. It is considered rude to just ask a
      question without searching the archives: your problem may already have
      been solved for somebody else!  This is true for most, if not all,
      mailing lists and not only for this particular list! Look in the
      documentation that came with RRDtool for the location and usage of the
      list.

      I suggest you take a moment to subscribe to the mailing list right now
      by sending an email to <rrd-users-request@list.ee.ethz.ch> with a
      subject of "subscribe". If you ever want to leave this list, you write
      an email to the same address but now with a subject of "unsubscribe".







                                    - 2 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      HHHHoooowwww wwwwiiiillllllll yyyyoooouuuu hhhheeeellllpppp mmmmeeee ????

      By giving you some detailed descriptions with detailed examples.  It
      is assumed that following the instructions in the order presented will
      give you enough knowledge of RRDtool to experiment for yourself.  If
      it doesn't work the first time, don't give up. Reread the stuff that
      you did understand, you may have missed something.  By following the
      examples you get some hands-on experience and, even more important,
      some background information of how it works.

      You will need to know something about hexadecimal numbers. If you
      don't then start with reading bin_dec_hex before you continue here.

      YYYYoooouuuurrrr ffffiiiirrrrsssstttt RRRRoooouuuunnnndddd RRRRoooobbbbiiiinnnn DDDDaaaattttaaaabbbbaaaasssseeee

      In my opinion the best way to learn something is to actually do it.
      Why not start right now?  We will create a database, put some values
      in it and extract this data again.  Your output should be the same as
      the output that is included in this document.

      We will start with some easy stuff and compare a car with a router, or
      compare kilometers (miles if you wish) with bits and bytes. It's all
      the same: some number over some time.

      Assume we have a device that transfers bytes to and from the Internet.
      This device keeps a counter that starts at zero when it is turned on,
      increasing with every byte that is transfered. This counter will have
      a maximum value, if that value is reached and an extra byte is
      counted, the counter starts all over at zero. This is the same as many
      counters in the world such as the mileage counter in a car.  Most
      discussions about networking talk about bits per second so lets get
      used to that right away. Assume a byte is eight bits and start to
      think in bits not bytes. The counter, however, still counts bytes !
      In the SNMP world most of the counters are 32 bits. That means they
      are counting from 0 to 4294967295. We will use these values in the
      examples.  The device, when asked, returns the current value of the
      counter. We know the time that has passes since we last asked so we
      now know how many bytes have been transfered ***on average*** per
      second. This is not very hard to calculate. First in words, then in
      calculations:

      1. Take the current counter, subtract the previous value from it.

      2. Do the same with the current time and the previous time.

      3. Divide the outcome of (1) by the outcome of (2), the result is the
         amount of bytes per second. Multiply by eight to get the number of
         bits per second (bps).

        bps = (counter_now - counter_before) / (time_now - time_before) * 8



                                    - 3 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      For some people it may help to translate this to a automobile example:
      Do not try this example, and if you do, don't blame me for the
      results.

      People who are not used to think in kilometers per hour can translate
      most into miles per hour by dividing km by 1.6 (close enough).  I will
      use the following abbreviations:

       M:    meter
       KM:   kilometer (= 1000 meters).
       H:    hour
       S:    second
       KM/H: kilometers per hour
       M/S:  meters per second

      You're driving a car. At 12:05 you read the counter in the dashboard
      and it tells you that the car has moved 12345 KM until that moment.
      At 12:10 you look again, it reads 12357 KM. This means you have
      traveled 12 KM in five minutes. A scientist would translate that into
      meters per second and this makes a nice comparison towards the problem
      of (bytes per five minutes) versus (bits per second).

      We traveled 12 kilometers which is 12000 meters. We did that in five
      minutes which translates into 300 seconds. Our speed is 12000M / 300S
      equals 40 M/S.

      We could also calculate the speed in KM/H: 12 times five minutes is an
      hour so we have to multiply 12 KM by 12 to get 144 KM/H.  For our
      native English speaking friends: that's 90 MPH so don't try this
      example at home or where I live :)

      Remember: these numbers are averages only.  There is no way to figure
      out from the numbers, if you drove at a constant speed.  There is an
      example later on in this tutorial that explains this.

      I hope you understand that there is no difference in calculating M/S
      or bps; only the way we collect the data is different. Even the K from
      kilo is the same as in networking terms k also means 1000.

      We will now create a database where we can keep all these interesting
      numbers. The method used to start the program may differ slightly from
      OS to OS but I assume you can figure it out if it works different on
      your OS. Make sure you do not overwrite any file on your system when
      executing the following command and type the whole line as one long
      line (I had to split it for readability) and skip all of the '\'
      characters.







                                    - 4 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



         rrdtool create test.rrd             \
                  --start 920804400          \
                  DS:speed:COUNTER:600:U:U   \
                  RRA:AVERAGE:0.5:1:24       \
                  RRA:AVERAGE:0.5:6:10

      (So enter: "rrdtool create test.rrd --start 920804400 DS ...")

      WWWWhhhhaaaatttt hhhhaaaassss bbbbeeeeeeeennnn ccccrrrreeeeaaaatttteeeedddd ????

      We created the round robin database called test (test.rrd) which
      starts at noon the day I started (7th of march, 1999) writing this
      document. It holds one data source (DS) named "speed" that gets built
      from a counter. This counter is read every five minutes (default) In
      the same database two round robin archives (RRAs) are kept, one
      averages the data every time it is read (eg there's nothing to
      average) and keeps 24 samples (24 times 5 minutes is 2 hours). The
      other averages 6 values (half hour) and contains 10 of such averages
      (eg 5 hours) The remaining options will be discussed later on.

      RRDtool works with special time stamps coming from the UNIX world.
      This time stamp is the number of seconds that passed since January 1st
      1970 UTC.  This time stamp is translated into local time and it will
      therefore look different for the different time zones.

      Chances are that you are not in the same part of the world as I am.
      This means your time zone is different. In all examples where I talk
      about time, the hours may be wrong for you. This has little effect on
      the results of the examples, just correct the hours while reading.  As
      an example: where I will see "12:05" the UK folks will see "11:05".

      We now have to fill our database with some numbers. We'll pretend to
      have read the following numbers:

       12:05  12345 KM
       12:10  12357 KM
       12:15  12363 KM
       12:20  12363 KM
       12:25  12363 KM
       12:30  12373 KM
       12:35  12383 KM
       12:40  12393 KM
       12:45  12399 KM
       12:50  12405 KM
       12:55  12411 KM
       13:00  12415 KM
       13:05  12420 KM
       13:10  12422 KM
       13:15  12423 KM




                                    - 5 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      We fill the database as follows:

       rrdtool update test.rrd 920804700:12345 920805000:12357 920805300:12363
       rrdtool update test.rrd 920805600:12363 920805900:12363 920806200:12373
       rrdtool update test.rrd 920806500:12383 920806800:12393 920807100:12399
       rrdtool update test.rrd 920807400:12405 920807700:12411 920808000:12415
       rrdtool update test.rrd 920808300:12420 920808600:12422 920808900:12423

      This reads: update our test database with the following numbers

       time 920804700, value 12345
       time 920805000, value 12357

      etcetera.

      As you can see, it is possible to feed more than one value into the
      database in one command. I had to stop at three for readability but
      the real maximum is OS dependent.

      We can now retrieve the data from our database using "rrdtool fetch":

       rrdtool fetch test.rrd AVERAGE --start 920804400 --end 920809200

      It should return the following output:

                      speed

       920804700:       NaN
       920805000:      0.04
       920805300:      0.02
       920805600:      0.00
       920805900:      0.00
       920806200:      0.03
       920806500:      0.03
       920806800:      0.03
       920807100:      0.02
       920807400:      0.02
       920807700:      0.02
       920808000:      0.01
       920808300:      0.02
       920808600:      0.01
       920808900:      0.00
       920809200:       NaN

      If it doesn't, something may be wrong.  Perhaps your OS will print
      "NaN" in a different form.  It represents "Not A Number".  If your OS
      writes "U" or "UNKN" or something similar that's okay.  If something
      else is wrong, it will probably be due to an error you made (assuming
      that my tutorial is correct of course :-). In that case: delete the
      database and try again.



                                    - 6 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      What this output represents will become clear in the rest of the
      tutorial.

      IIIItttt iiiissss ttttiiiimmmmeeee ttttoooo ccccrrrreeeeaaaatttteeee ssssoooommmmeeee ggggrrrraaaapppphhhhiiiiccccssss

      Try the following command:

       rrdtool graph speed.gif                                 \
               --start 920804400 --end 920808000               \
               DEF:myspeed=test.rrd:speed:AVERAGE              \
               LINE2:myspeed#FF0000

      This will create speed.gif which starts at 12:00 and ends at 13:00.
      There is a definition of variable myspeed, it is the data from RRA
      "speed" out of database "test.rrd". The line drawn is 2 pixels high,
      and comes from variable myspeed. The color is red.  You'll notice that
      the start of the graph is not at 12:00 but at 12:05 and this is
      because we have insufficient data to tell the average before that
      time. This will only happen when you miss some samples, this will not
      happen a lot, hopefully.

      If this has worked: congratulations! If not, check what went wrong.

      The colors are built up from red, green and blue. For each of the
      components, you specify how much to use in hexadecimal where 00 means
      not included and FF means fully included.  The "color" white is a
      mixture of red, green and blue: FFFFFF The "color" black is all colors
      off: 000000

         red     #FF0000
         green   #00FF00
         blue    #0000FF
         magenta #FF00FF     (mixed red with blue)
         gray    #555555     (one third of all components)

      The GIF you just created can be displayed using your favorite image
      viewer.  Web browsers will display the GIF via the URL
      "file://the/path/to/speed.gif"

      GGGGrrrraaaapppphhhhiiiiccccssss wwwwiiiitttthhhh ssssoooommmmeeee mmmmaaaatttthhhh

      When looking at the image, you notice that the horizontal axis is
      labeled 12:10, 12:20, 12:30, 12:40 and 12:50. The two remaining times
      (12:00 and 13:00) would not be displayed nicely so they are skipped.
      The vertical axis displays the range we entered. We provided
      kilometers and when divided by 300 seconds, we get very small numbers.
      To be exact, the first value was 12 (12357-12345) and divided by 300
      this makes 0.04, which is displayed by RRDtool as "40 m" meaning
      "40/1000". The "m" has nothing to do with meters, kilometers or
      millimeters! RRDtool doesn't know about all this, it just works with



                                    - 7 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      numbers and not with meters...

      What we did wrong was that we should have measured in meters, this
      would have been (12357000-12345000)/300 = 12000/300 = 40.

      Let's correct that. We could recreate our database and store the
      correct data but there is a better way: do some calculations while
      creating the gif file !

         rrdtool graph speed2.gif                           \
            --start 920804400 --end 920808000               \
            --vertical-label m/s                            \
            DEF:myspeed=test.rrd:speed:AVERAGE              \
            CDEF:realspeed=myspeed,1000,*                   \
            LINE2:realspeed#FF0000

      After viewing this GIF, you notice the "m" has disappeared. This it
      what the correct result would be. Also, a label has been added to the
      image.  Apart from the things mentioned above, the GIF should be the
      same.

      The calculations are in the CDEF part and are in Reverse Polish
      Notation ("RPN"). What it says is: "take the data source myspeed and
      the number 1000; multiply those". Don't bother with RPN yet, it will
      be explained later on in more detail. Also, you may want to read my
      tutorial on CDEFs and Steve Rader's tutorial on RPN. But first finish
      this tutorial.

      Hang on! If we can multiply values with 1000, it should also be
      possible to display kilometers per hour from the same data!

      To change a value that is measured in meters per second:
       -*- Calculate meters per hour:     value * 3600
       -*- Calculate kilometers per hour: value / 1000
       -*- Together this makes:           value * (3600/1000) == value * 3.6

      In our example database we made a mistake and we need to compensate
      for this by multiplying with 1000. Applying that correction:
       -*- value * 3.6  *1000 == value * 3600

      Now let's create this GIF, and add some more magic ...












                                    - 8 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



         rrdtool graph speed3.gif                           \
            --start 920804400 --end 920808000               \
            --vertical-label km/h                           \
            DEF:myspeed=test.rrd:speed:AVERAGE              \
            "CDEF:kmh=myspeed,3600,*"                       \
            CDEF:fast=kmh,100,GT,kmh,0,IF                   \
            CDEF:good=kmh,100,GT,0,kmh,IF                   \
            HRULE:100#0000FF:"Maximum allowed"              \
            AREA:good#00FF00:"Good speed"                   \
            AREA:fast#FF0000:"Too fast"

      This looks much better. Speed in KM/H and even an extra line with the
      maximum allowed speed (on the road I travel at). I also changed the
      colors used to display speed and changed it from a line into an area.

      The calculations are more complex now. For the "good" speed they are:

         Check if kmh is greater than 100    ( kmh,100 ) GT
         If so, return 0, else kmh           ((( kmh,100 ) GT ), 0, kmh) IF

      For the other speed:

         Check if kmh is greater than 100    ( kmh,100 ) GT
         If so, return kmh, else return 0    ((( kmh,100) GT ), kmh, 0) IF

      GGGGrrrraaaapppphhhhiiiiccccssss MMMMaaaaggggiiiicccc

      I like to believe there are virtually no limits to how RRDtool graph
      can manipulate data. I will not explain how it works, but look at the
      following GIF:

         rrdtool graph speed4.gif                           \
            --start 920804400 --end 920808000               \
            --vertical-label km/h                           \
            DEF:myspeed=test.rrd:speed:AVERAGE              \
            "CDEF:kmh=myspeed,3600,*"                       \
            CDEF:fast=kmh,100,GT,100,0,IF                   \
            CDEF:over=kmh,100,GT,kmh,100,-,0,IF             \
            CDEF:good=kmh,100,GT,0,kmh,IF                   \
            HRULE:100#0000FF:"Maximum allowed"              \
            AREA:good#00FF00:"Good speed"                   \
            AREA:fast#550000:"Too fast"                     \
            STACK:over#FF0000:"Over speed"

      Let's create a quick and dirty HTML page to view three GIFs:








                                    - 9 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



         <HTML><HEAD><TITLE>Speed</TITLE></HEAD><BODY>
         <IMG src="speed2.gif" alt="Speed in meters per second">
         <BR>
         <IMG src="speed3.gif" alt="Speed in kilometers per hour">
         <BR>
         <IMG src="speed4.gif" alt="Traveled too fast?">
         </BODY></HTML>

      Name the file "speed.html" or similar, and view it.

      Now, all you have to do is measure the values regularly and update the
      database.  When you want to view the data, recreate the GIFs and make
      sure to refresh them in your browser. (Note: just clicking reload may
      not be enough; Netscape in particular has a problem doing so and
      you'll need to click reload while pressing the shift key).

      UUUUppppddddaaaatttteeeessss iiiinnnn RRRReeeeaaaalllliiiittttyyyy

      We've already used the "update" command: it took one or more
      parameters in the form of "<time>:<value>". You'll be glad to know
      that you can get the current time by filling in a "N" as the time.  If
      you wish, you can also use the "time" function in perl.  The shortest
      example in this doc :)

         perl -e 'print time, "\n" '

      How you can run a program on regular intervals is OS specific. But
      here's an example in pseudo code:

         Get the value, put it in variable "$speed"
         rrdtool update speed.rrd N:$speed

      (Do not try this with our test database, it is used in further
      examples)

      This is all. Run this script every five minutes. When you need to know
      what the graphics look like, run the examples above. You could put
      them in a script. After running that script, view index.html

      SSSSoooommmmeeee wwwwoooorrrrddddssss oooonnnn SSSSNNNNMMMMPPPP

      I can imagine very few people will be able to get real data from their
      car every five minutes, all other people will have to settle for some
      other kind of counter. You could measure the number of pages printed
      by a printer, the coffee made by the coffee machine, a device that
      counts the electricity used, whatever. Any incrementing counter can be
      monitored and graphed using the stuff you learned until now. Later on
      we will also be able to monitor other types of values like
      temperature.  Most people will use the counter that keeps track of
      octets (bytes) transfered by a network device so we have to do just



                                   - 10 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      that. We will start with a description of how to collect data.  Some
      people will make a remark that there are tools who can do this data
      collection for you. They are right!  However, I feel it is important
      that you understand they are not necessary.  When you have to
      determine why things went wrong you need to know how they work.

      One tool used in the example has been talked about very briefly in the
      beginning of this document, it is called SNMP. It is a way of talking
      to equipment. The tool I use below is called "snmpget" and this is how
      it works:

         snmpget device password OID

      For device you substitute the name, or the IP address, of your device.
      For password you use the "community read string" as it is called in
      the SNMP world.  For some devices the default of "public" might work,
      however this can be disabled, altered or protected for privacy and
      security reasons.  Read the documentation that comes with your device
      or program.

      Then there is this third parameter, called OID, which means "object
      identifier".

      When you start to learn about SNMP it looks very confusing. It isn't
      all that difficult when you look at the Management Information Base
      ("MIB").  It is an upside-down tree that describes data, with a single
      node as the root and from there a number of branches.  These branches
      end up in another node, they branch out, etc.  All the branches have a
      name and they form the path that we follow all the way down.  The
      branches that we follow are named: iso, org, dod, internet, mgmt and
      mib-2.  These names can also be written down as numbers and are 1 3 6
      1 2 1.

         iso.org.dod.internet.mgmt.mib-2 (1.3.6.1.2.1)

      There is a lot of confusion about the leading dot that some programs
      use.  There is *no* leading dot in an OID.  However, some programs can
      use above part of OIDs as a default.  To indicate the difference
      between abbreviated OIDs and full OIDs they need a leading dot when
      you specify the complete OID.  Often those programs will leave out the
      default portion when returning the data to you.  To make things worse,
      they have several default prefixes ...

      Right, lets continue to the start of our OID: we had 1.3.6.1.2.1 From
      there, we are especially interested in the branch "interfaces" which
      has number 2 (eg 1.3.6.1.2.1.2 or 1.3.6.1.2.1.interfaces).

      First, we have to get some SNMP program. First look if there is a
      pre-compiled package available for your OS. This is the preferred way.
      If not, you will have to get yourself the sources and compile those.



                                   - 11 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      The Internet is full of sources, programs etc. Find information using
      a search engine or whatever you prefer. As a suggestion: look for
      CMU-SNMP.  It is commonly used.

      Assume you got the program. First try to collect some data that is
      available on most systems. Remember: there is a short name for the
      part of the tree that interests us most in the world we live in!

      I will use the short version as I think this document is large enough
      as it is. If that doesn't work for you, prefix with .1.3.6.1.2.1 and
      try again.  Also, Read The Fine Manual.  Skip the parts you cannot
      understand yet, you should be able to find out how to start the
      program and use it.

         snmpget myrouter public system.sysDescr.0

      The device should answer with a description of itself, perhaps empty.
      Until you got a valid answer from a device, perhaps using a different
      "password", or a different device, there is no point in continuing.

         snmpget myrouter public interfaces.ifNumber.0

      Hopefully you get a number as a result, the number of interfaces.  If
      so, you can carry on and try a different program called "snmpwalk".

         snmpwalk myrouter public interfaces.ifTable.ifEntry.ifDescr

      If it returns with a list of interfaces, you're almost there.  Here's
      an example:
         [user@host /home/alex]$ snmpwalk cisco public 2.2.1.2

         interfaces.ifTable.ifEntry.ifDescr.1 = "BRI0: B-Channel 1"
         interfaces.ifTable.ifEntry.ifDescr.2 = "BRI0: B-Channel 2"
         interfaces.ifTable.ifEntry.ifDescr.3 = "BRI0" Hex: 42 52 49 30
         interfaces.ifTable.ifEntry.ifDescr.4 = "Ethernet0"
         interfaces.ifTable.ifEntry.ifDescr.5 = "Loopback0"

      On this cisco equipment, I would like to monitor the "Ethernet0"
      interface and see that it is number four. I try:

         [user@host /home/alex]$ snmpget cisco public 2.2.1.10.4 2.2.1.16.4

         interfaces.ifTable.ifEntry.ifInOctets.4 = 2290729126
         interfaces.ifTable.ifEntry.ifOutOctets.4 = 1256486519

      So now I have two OIDs to monitor and they are (in full, this time):

         1.3.6.1.2.1.2.2.1.10

      and



                                   - 12 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



         1.3.6.1.2.1.2.2.1.16

      both with an interface number of 4.

      Don't get fooled, this wasn't my first try. It took some time for me
      too to understand what all these numbers mean, it does help a lot when
      they get translated into descriptive text... At least, when people are
      talking about MIBs and OIDs you know what it's all about.  Do not
      forget the interface number (0 if it is not interface dependent) and
      try snmpwalk if you don't get an answer from snmpget.

      If you understand above part, and get numbers from your device,
      continue on with this tutorial. If not, then go back and re-read this
      part.

      AAAA RRRReeeeaaaallll WWWWoooorrrrlllldddd EEEExxxxaaaammmmpppplllleeee

      Let the fun begin. First, create a new database. It contains data from
      two counters, called input and output. The data is put into archives
      that average it. They take 1, 6, 24 or 288 samples at a time.  They
      also go into archives that keep the maximum numbers. This will be
      explained later on. The time in-between samples is 300 seconds, a good
      starting point, which is the same as five minutes.

       1 sample "averaged" stays 1 period of 5 minutes
       6 samples averaged become one average on 30 minutes
       24 samples averaged become one average on 2 hours
       288 samples averaged become one average on 1 day

      Lets try to be compatible with MRTG: MRTG stores about the following
      amount of data:

       600 5-minute samples:    2   days and 2 hours
       600 30-minute samples:  12.5 days
       600 2-hour samples:     50   days
       732 1-day samples:     732   days

      These ranges are appended so the total amount of data kept is
      approximately 797 days.  RRDtool stores the data differently, it
      doesn't start the "weekly" archive where the "daily" archive stopped.
      For both archives the most recent data will be near "now" and
      therefore we will need to keep more data than MRTG does!

      We will need:

       600 samples of 5 minutes  (2 days and 2 hours)
       700 samples of 30 minutes (2 days and 2 hours, plus 12.5 days)
       775 samples of 2 hours    (above + 50 days)
       797 samples of 1 day      (above + 732 days, rounded up to 797)




                                   - 13 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



         rrdtool create myrouter.rrd         \
                  DS:input:COUNTER:600:U:U   \
                  DS:output:COUNTER:600:U:U  \
                  RRA:AVERAGE:0.5:1:600      \
                  RRA:AVERAGE:0.5:6:700      \
                  RRA:AVERAGE:0.5:24:775     \
                  RRA:AVERAGE:0.5:288:797    \
                  RRA:MAX:0.5:1:600          \
                  RRA:MAX:0.5:6:700          \
                  RRA:MAX:0.5:24:775         \
                  RRA:MAX:0.5:288:797

      Next thing to do is collect data and store it. Here is an example.  It
      is written partially in pseudo code so you will have to find out what
      to do exactly on your OS to make it work.

         while not the end of the universe
         do
            get result of
               snmpget router community 2.2.1.10.4
            into variable $in
            get result of
               snmpget router community 2.2.1.16.4
            into variable $out

            rrdtool update myrouter.rrd N:$in:$out

            wait for 5 minutes
         done

      Then, after collecting data for a day, try to create an image using:

         rrdtool graph myrouter-day.gif --start -86400 \
                  DEF:inoctets=myrouter.rrd:input:AVERAGE \
                  DEF:outoctets=myrouter.rrd:output:AVERAGE \
                  AREA:inoctets#00FF00:"In traffic" \
                  LINE1:outoctets#0000FF:"Out traffic"

      This should produce a picture with one day worth of traffic.  One day
      is 24 hours of 60 minutes of 60 seconds: 24*60*60=86400, we start at
      now minus 86400 seconds. We define (with DEFs) inoctets and outoctets
      as the average values from the database myrouter.rrd and draw an area
      for the "in" traffic and a line for the "out" traffic.

      View the image and keep logging data for a few more days.  If you
      like, you could try the examples from the test database and see if you
      can get various options and calculations working.

      Suggestion:




                                   - 14 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      Display in bytes per second and in bits per second. Make the Ethernet
      graphics go red if they are over four megabits per second.

      CCCCoooonnnnssssoooolllliiiiddddaaaattttiiiioooonnnn FFFFuuuunnnnccccttttiiiioooonnnnssss

      A few paragraphs back I mentioned the possibility of keeping the
      maximum values instead of the average values. Let's go into this a bit
      more.

      Recall all the stuff about the speed of the car. Suppose we drove at
      144 KM/H during 5 minutes and then were stopped by the police for 25
      minutes.  At the end of the lecture we would take our laptop and
      create+view the image taken from the database. If we look at the
      second RRA we did create, we would have the average from 6 samples.
      The samples measured would be 144+0+0+0+0+0=144, divided by 30
      minutes, corrected for the error by 1000, translated into KM/H, with a
      result of 24 KM/H.  I would still get a ticket but not for speeding
      anymore :)

      Obviously, in this case, we shouldn't look at the averages. In some
      cases they are handy. If you want to know how much KM you had
      traveled, the picture would be the right one to look at. On the other
      hand, for the speed that we traveled at, the maximum number seen is
      much more valuable. (later we will see more types)

      It is the same for data. If you want to know the amount, look at the
      averages. If you want to know the rate, look at the maximum.  Over
      time, they will grow apart more and more. In the last database we have
      created, there are two archives that keep data per day. The archive
      that keeps averages will show low numbers, the archive that shows
      maxima will have higher numbers.  For my car this would translate in
      averages per day of 96/24=4 KM/H (as I travel about 94 kilometers on a
      day) during week days, and maximum of 120 KM/H on weekdays (my top
      speed that I reach every day).

      Big difference. Do not look at the second graph to estimate the
      distances that I travel and do not look at the first graph to estimate
      my speed. This will work if the samples are close together, as they
      are in five minutes, but not if you average.

      On some days, I go for a long ride. If I go across Europe and travel
      for over 12 hours, the first graph will rise to about 60 KM/H. The
      second one will show 180 KM/H. This means that I traveled a distance
      of 60 KM/H times 24 H = 1440 KM. I did this with a higher speed and a
      maximum around 180 KM/H. This doesn't mean that I traveled for 8 hours
      at a constant speed of 180 KM/H !  This is a real example: go with the
      flow through Germany (fast!) and stop a few times for gas and coffee.
      Drive slowly through Austria and the Netherlands. Be careful in the
      mountains and villages. If you would look at the graphs created from
      the five-minute averages you would get a totally different picture.



                                   - 15 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      You would see the same values on the average and maximum graphs
      (provided I measured every 300 seconds).  You would be able to see
      when I stopped, when I was in top gear, when I drove over fast hiways
      etc. The granularity of the data is much higher, so you can see more.
      However, this takes 12 samples per hour, or 288 values per day, so it
      would be too much to keep for a long period of time. Therefore we
      average it, eventually to one value per day. From this one value, we
      cannot see much detail.

      Make sure you understand the last few paragraphs. There is no value in
      only a line and a few axis, you need to know what they mean and
      interpret the data in a good way. This is true for all data.

      The biggest mistake you can make is to use the collected data for
      something that it is not suitable for. You would be better off if you
      would not have the graphics at all in that case.

      LLLLeeeetttt''''ssss rrrreeeevvvviiiieeeewwww wwwwhhhhaaaatttt yyyyoooouuuu nnnnoooowwww sssshhhhoooouuuulllldddd kkkknnnnoooowwww....

      You now know how to create a database. You can put the numbers in it,
      get them out again by creating an image, do math on the data from the
      database and view the outcome instead of the raw data.  You know about
      the difference between averages and maxima, and when to use which (or
      at least you have an idea).

      RRDtool can do more than what we have learned up to now. Before you
      continue with the rest of this doc, I recommend that you reread from
      the start and try some modifications on the examples. Make sure you
      fully understand everything. It will be worth the effort and helps you
      not only with the rest of this doc but also in your day to day
      monitoring long after you read this introduction.

      DDDDaaaattttaaaa SSSSoooouuuurrrrcccceeee TTTTyyyyppppeeeessss

      All right, you feel like continuing. Welcome back and get ready for an
      increased speed in the examples and explanation.

      You know that in order to view a counter over time, you have to take
      two numbers and divide the difference of them between the time lapsed.
      This makes sense for the examples I gave you but there are other
      possibilities.  For instance, I'm able to retrieve the temperature
      from my router in three places namely the inlet, the so called hot-
      spot and the exhaust.  These values are not counters.  If I take the
      difference of the two samples and divide that by 300 seconds I would
      be asking for the temperature change per second.  Hopefully this is
      zero! If not, the computerroom is on fire :)

      So, what can we do ?  We can tell RRDtool to store the values we
      measure directly as they are (this is not entirely true but close
      enough). The graphs we make will look much better, they will show a



                                   - 16 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      rather constant value. I know when the router is busy (it works -> it
      uses more electricity -> it generates more heat -> the temperature
      rises). I know when the doors are left open (the room is cooled -> the
      warm air from the rest of the building flows into the computer room ->
      the inlet temperature rises) etc. The data type we use when creating
      the database before was counter, we now have a different data type and
      thus a different name for it. It is called GAUGE. There are more such
      data types:

       - COUNTER   we already know this one
       - GAUGE     we just learned this one
       - DERIVE
       - ABSOLUTE

      The two new types are DERIVE and ABSOLUTE. Absolute can be used like
      counter with one difference: RRDtool assumes the counter is reset when
      it's read. That is: its delta is known without calculation by RRDtool
      whereas RRDtool needs to calculate it for the counter type.  Example:
      our first example (12345, 12357, 12363, 12363) would read: unknown,
      12, 6, 0. The rest of the calculations stay the same.  The other one,
      derive, is like counter. Unlike counter, it can also decrease so it
      can have a negative delta. Again, the rest of the calculations stay
      the same.

      Let's try them all:

         rrdtool create all.rrd --start 978300900 \
                  DS:a:COUNTER:600:U:U \
                  DS:b:GAUGE:600:U:U \
                  DS:c:DERIVE:600:U:U \
                  DS:d:ABSOLUTE:600:U:U \
                  RRA:AVERAGE:0.5:1:10
         rrdtool update all.rrd \
                  978301200:300:1:600:300    \
                  978301500:600:3:1200:600   \
                  978301800:900:5:1800:900   \
                  978302100:1200:3:2400:1200 \
                  978302400:1500:1:2400:1500 \
                  978302700:1800:2:1800:1800 \
                  978303000:2100:4:0:2100    \
                  978303300:2400:6:600:2400  \
                  978303600:2700:4:600:2700  \
                  978303900:3000:2:1200:3000
         rrdtool graph all1.gif -s 978300600 -e 978304200 -h 400 \
                  DEF:linea=all.rrd:a:AVERAGE LINE3:linea#FF0000:"Line A" \
                  DEF:lineb=all.rrd:b:AVERAGE LINE3:lineb#00FF00:"Line B" \
                  DEF:linec=all.rrd:c:AVERAGE LINE3:linec#0000FF:"Line C" \
                  DEF:lined=all.rrd:d:AVERAGE LINE3:lined#000000:"Line D"





                                   - 17 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      RRRRRRRRDDDDttttoooooooollll uuuunnnnddddeeeerrrr tttthhhheeee MMMMiiiiccccrrrroooossssccccooooppppeeee

      o+ Line A is a counter so it should continuously increment and RRDtool
        should calculate the differences. Also, RRDtool needs to divide the
        difference by the amount of time lapsed. This should end up as a
        straight line at 1 (the deltas are 300, the time is 300).

      o+ Line B is of type gauge. These are "real" values so they should
        match what we put in: a sort of a wave.

      o+ Line C is derive. It should be a counter that can decrease. It does
        so between 2400 and 0, with 1800 in-between.

      o+ Line D is of type absolute. This is like counter but it works on
        values without calculating the difference. The numbers are the same
        and as you can see (hopefully) this has a different result.

      This translates in the following values, starting at 23:10 and ending
      at 00:10 the next day (where U means unknown/unplotted):

       - Line A:  u  u  1  1  1  1  1  1  1  1  1  u
       - Line B:  u  1  3  5  3  1  2  4  6  4  2  u
       - Line C:  u  u  2  2  2  0 -2 -6  2  0  2  u
       - Line D:  u  1  2  3  4  5  6  7  8  9 10  u

      If your GIF shows all this, you know you have typed the data correct,
      the RRDtool executable is working properly, your viewer doesn't fool
      you and you successfully entered the year 2000 :) You could try the
      same example four times, each time with only one of the lines.

      Let's go over the data again:

      o+ Line A: 300,600,900 and so on. The counter delta is a constant 300
        and so it the time delta. A number divided by itself is always 1
        (except when dividing by zero which is undefined/illegal).  Why is
        it that the first point is unknown ? We do know what we put into the
        database ? True ! But we didn't have a value to calculate the delta
        from so we don't know where we started. It would be wrong to assume
        we started at zero so we don't !

      o+ Line B: There is nothing to calculate. The numbers are as is.

      o+ Line C: Again, the start-out value is unknown. The same story is
        valid like for line A. In this case the deltas are not constant so
        the line is not. If we would put the same numbers in the database as
        we did for line A, we would have gotten the same line. Unlike type
        counter, this type can decrease and I hope to show you later on why
        there is a difference.

      o+ Line D: Here the device calculates the deltas. Therefore we DO know



                                   - 18 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



        the first delta and it is plotted. We had the same input as with
        line A but the meaning of this input is different. Therefore the
        line is different.  In this case the deltas increase each time with
        300. The time delta stays at a constant 300 and therefore the
        division of the two gives increasing results.

      CCCCoooouuuunnnntttteeeerrrr WWWWrrrraaaappppssss

      There are a few more basics to show. Some important options are still
      to be covered and we haven't look at counter wraps yet. First the
      counter wrap: In our car we notice that our counter shows 999987. We
      travel 20 KM and the counter should go to 1000007. Unfortunately,
      there are only six digits on our counter so it really shows 000007. If
      we would plot that on a type DERIVE, it would mean that the counter
      was set back 999980 KM. It wasn't, and there has to be some protection
      for this. This protection is only available for type COUNTER which
      should be used for this kind of counter anyways. How does it work ?
      Type counter should never decrease and therefore RRDtool must assume
      it wrapped if it does decrease !  If the delta is negative, this can
      be compensated for by adding the maximum value of the counter + 1. For
      our car this would be:

       Delta = 7 - 999987 = -999980    (instead of 1000007-999987=20)

       Real delta = -999980 + 999999 + 1 = 20

      At the time of writing this document, RRDtool knows of counters that
      are either 32 bits or 64 bits of size. These counters can handle the
      following different values:

       - 32 bits: 0 ..           4294967295
       - 64 bits: 0 .. 18446744073709551615

      If these numbers look strange to you, you would like to view them in
      their hexadecimal form:

       - 32 bits: 0 ..         FFFFFFFF
       - 64 bits: 0 .. FFFFFFFFFFFFFFFF

      RRDtool handles both counters the same. If an overflow occurs and the
      delta would be negative, RRDtool first adds the maximum of a small
      counter + 1 to the delta. If the delta is still negative, it had to be
      the large counter that wrapped. Add the maximum possible value of the
      large counter + 1 and subtract the falsely added small value.  There
      is a risk in this: suppose the large counter wrapped while adding a
      huge delta, it could happen in theory that adding the smaller value
      would make the delta positive. In this unlikely case the results would
      not be correct. The increase should be nearly as high as the maximum
      counter value for that to happen so chances are you would have several
      other problems as well and this particular problem would not even be



                                   - 19 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      worth thinking about. Even though I did include an example of it so
      you can judge that for yourself.

      The next section gives you some numerical examples for counter-wraps.
      Try to do the calculations yourself or just believe me if your
      calculator can't handle the numbers :)

      Correction numbers:

       - 32 bits: (4294967295+1) =                                 4294967296
       - 64 bits: (18446744073709551615+1)-correction1 = 18446744069414584320

       Before:        4294967200
       Increase:             100
       Should become: 4294967300
       But really is:          4
       Delta:        -4294967196
       Correction1:  -4294967196 +4294967296 = 100

       Before:        18446744073709551000
       Increase:                       800
       Should become: 18446744073709551800
       But really is:                  184
       Delta:        -18446744073709550816
       Correction1:  -18446744073709550816 +4294967296 = -18446744069414583520
       Correction2:  -18446744069414583520 +18446744069414584320 = 800

       Before:        18446744073709551615 ( maximum value )
       Increase:      18446744069414584320 ( absurd increase, minimum for
       Should become: 36893488143124135935             this example to work )
       But really is: 18446744069414584319
       Delta:                  -4294967296
       Correction1:  -4294967296 + 4294967296 = 0
       (not negative -> no correction2)

       Before:        18446744073709551615 ( maximum value )
       Increase:      18446744069414584319 ( one less increase )
       Should become: 36893488143124135934
       But really is: 18446744069414584318
       Delta:                  -4294967297
       Correction1:  -4294967297 +4294967296 = -1
       Correction2:  -1 +18446744069414584320 = 18446744069414584319

      As you can see from the last two examples, you need strange numbers
      for RRDtool to fail (provided it's bug free of course) so this should
      not happen.  However, SNMP or whatever method you choose to collect
      the data might also report wrong numbers occasionally.  We can't
      prevent all errors but there are some things we can do.  The RRDtool
      "create" command takes two special parameters for this. They define
      the minimum and maximum allowed value. Until now, we used "U", meaning



                                   - 20 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



      "unknown". If you provide values for one or both of them and if
      RRDtool receives values that are outside these limits, it will ignore
      those values. For a thermometer in degrees Celsius, the absolute
      minimum is just under -273. For my router, I can assume this minimum
      is much higher so I would say it is 10. The maximum temperature for my
      router I would state as 80. Any higher and the device would be out of
      order.  For my car, I would never expect negative numbers and also I
      would not expect numbers to be higher than 230. Anything else, and
      there must have been an error. Remember: the opposite is not true, if
      the numbers pass this check it doesn't mean that they are correct.
      Always judge the graph with a healthy dose of paranoia if it looks
      weird.

      DDDDaaaattttaaaa RRRReeeessssaaaammmmpppplllliiiinnnngggg

      One important feature of RRDtool has not been explained yet: It is
      virtually impossible to collect the data and feed it into RRDtool on
      exact intervals. RRDtool therefore interpolates the data so it is on
      exact intervals. If you do not know what this means or how it works,
      then here's the help you seek:

      Suppose a counter increases with exactly one for every second. You
      want to measure it in 300 seconds intervals. You should retrieve
      values that are exactly 300 apart. However, due to various
      circumstances you are a few seconds late and the interval is 303. The
      delta will also be 303 in that case. Obviously RRDtool should not put
      303 in the database and make you believe that the counter increased
      303 in 300 seconds.  This is where RRDtool interpolates: it alters the
      303 value as if it would have been stored earlier and it will be 300
      in 300 seconds.  Next time you are at exactly the right time. This
      means that the current interval is 297 seconds and also the counter
      increased with 297. Again RRDtool alters the value and stores 300 as
      it should be.

            in the RDD                 in reality

       time+000:   0 delta="U"   time+000:    0 delta="U"
       time+300: 300 delta=300   time+300:  300 delta=300
       time+600: 600 delta=300   time+603:  603 delta=303
       time+900: 900 delta=300   time+900:  900 delta=297

      Let's create two identical databases. I've chosen the time range
      920805000 to 920805900 as this goes very well with the example
      numbers.

         rrdtool create seconds1.rrd   \
            --start 920804700          \
            DS:seconds:COUNTER:600:U:U \
            RRA:AVERAGE:0.5:1:24




                                   - 21 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



         for Unix: cp seconds1.rrd seconds2.rrd
         for Dos:  copy seconds1.rrd seconds2.rrd
         for vms:  how would I know :)

         rrdtool update seconds1.rrd \
            920805000:000 920805300:300 920805600:600 920805900:900
         rrdtool update seconds2.rrd \
            920805000:000 920805300:300 920805603:603 920805900:900

         rrdtool graph seconds1.gif                       \
            --start 920804700 --end 920806200             \
            --height 200                                  \
            --upper-limit 1.05 --lower-limit 0.95 --rigid \
            DEF:seconds=seconds1.rrd:seconds:AVERAGE      \
            CDEF:unknown=seconds,UN                       \
            LINE2:seconds#0000FF                          \
            AREA:unknown#FF0000
         rrdtool graph seconds2.gif                       \
            --start 920804700 --end 920806200             \
            --height 200                                  \
            --upper-limit 1.05 --lower-limit 0.95 --rigid \
            DEF:seconds=seconds2.rrd:seconds:AVERAGE      \
            CDEF:unknown=seconds,UN                       \
            LINE2:seconds#0000FF                          \
            AREA:unknown#FF0000

      Both graphs should show the same.

 WWWWRRRRAAAAPPPPUUUUPPPP
      It's time to wrap up this document. You now know all the basics to be
      able to work with RRDtool and to read the documentation available.
      There is plenty more to discover about RRDtool and you will find more
      and more uses for the package. You could create easy graphics using
      just the examples provided and using only RRDtool. You could also use
      the front ends that are available.

 MMMMAAAAIIIILLLLIIIINNNNGGGGLLLLIIIISSSSTTTT
      Remember to subscribe to the mailing-list. Even if you are not
      answering the mails that come by, it helps both you and the rest. A
      lot of the stuff that I know about MRTG (and therefore about RRDtool)
      I've learned while just reading the list without posting to it. I did
      not need to ask the basic questions as they are answered in the FAQ
      (read it!) and in various mails by other users.  With thousands of
      users all over the world, there will always be people who ask
      questions that you can answer because you read this and other
      documentation and they didn't.

 SSSSEEEEEEEE AAAALLLLSSSSOOOO
      The RRDtool manpages




                                   - 22 -        Formatted:  August 20, 2003






 RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))                    1111....0000....44445555                     RRRRRRRRDDDDTTTTUUUUTTTTOOOORRRRIIIIAAAALLLL((((1111))))
 rrrrrrrrddddttttoooooooollll                                                             rrrrrrrrddddttttoooooooollll
                                 2222000000003333----00002222----22227777



 AAAAUUUUTTTTHHHHOOOORRRR
      I hope you enjoyed the examples and their descriptions. If you do,
      help other people by pointing them to this document when they are
      asking basic questions. They will not only get their answer but at the
      same time learn a whole lot more.

      Alex van den Bogaerdt <alex@ergens.op.het.net>














































                                   - 23 -        Formatted:  August 20, 2003



