


     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



     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 <tobi@oetiker.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 neither a
          beginning nor an end, you can go on and on and on. After a
          while, all the available places will be used and the process
          automatically reuses old locations. This way, the dataset
          will not grow in size and therefore requires no maintenance.
          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RRRRRDDDD????

          You name it, it will probably fit as long as it is some sort
          of time-series data. This means you have to 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 must be numerical but
          don't have to be integers, as is the case with MRTG (the
          next section will give more details on this more specialized
          application).




     Page 1                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          Many examples below 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
          SNMP can be used to query devices for the values of counters
          they keep. It is the value from those counters that we want
          to store 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 university's connection to the Internet. MRTG was later
          (ab-)used as a tool for graphing other data sources
          including temperature, speed, voltage, number of printouts
          and the like.

          Most likely you will start to use 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.  But 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 only need a sensor to measure the data and be able to
          feed the numbers into RRDtool. RRDtool then lets you create
          a database, store data in it, retrieve that data and create
          graphs in PNG format for display on a web browser. Those PNG
          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.

          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 pre-compiled 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



     Page 2                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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 one. 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, just write
          an email to the same address but now with a subject of
          "unsubscribe".

          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.  I assume 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 probably have a maximum value.
          If this value is reached and an extra byte is counted, the
          counter starts 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



     Page 3                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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
          4'294'967'295. 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
             (in seconds).

          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

          For some people it may help to translate this to an
          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 (= 1'000 meters).
           H:    hour
           S:    second
           KM/H: kilometers per hour
           M/S:  meters per second

          You are driving a car. At 12:05 you read the counter in the
          dashboard and it tells you that the car has moved 12'345 KM
          until that moment.  At 12:10 you look again, it reads 12'357
          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 toward the problem of (bytes
          per five minutes) versus (bits per second).

          We traveled 12 kilometers which is 12'000 meters. We did
          that in five minutes or 300 seconds. Our speed is 12'000M /
          300S or 40 M/S.

          We could also calculate the speed in KM/H: 12 times 5
          minutes is an hour, so we have to multiply 12 KM by 12 to
          get 144 KM/H.  For our native English speaking friends:



     Page 4                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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 1'000.

          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's. 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.

             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 writing this
          document, 7th of March, 1999 (this date translates to
          920'804'400 seconds as explained below). Our database holds
          one data source (DS) named "speed" that represents 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 (e.g.,
          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 such averages (e.g., 5 hours).

          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.  The time stamp value is
          translated into local time and it will therefore look
          different for different time zones.

          Chances are that you are not in the same part of the world



     Page 5                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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

          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 per line 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:




     Page 6                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



                                    speed

           920804700: nan
           920805000: 4.0000000000e-02
           920805300: 2.0000000000e-02
           920805600: 0.0000000000e+00
           920805900: 0.0000000000e+00
           920806200: 3.3333333333e-02
           920806500: 3.3333333333e-02
           920806800: 3.3333333333e-02
           920807100: 2.0000000000e-02
           920807400: 2.0000000000e-02
           920807700: 2.0000000000e-02
           920808000: 1.3333333333e-02
           920808300: 1.6666666667e-02
           920808600: 6.6666666667e-03
           920808900: 3.3333333333e-03
           920809200: nan

          If it doesn't, something may be wrong.  Perhaps your OS will
          print "NaN" in a different form. "NaN" stands for "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.  Sometimes things change.  This
          example used to provide numbers like "0.04" in stead of
          "4.00000e-02".  Those are really the same numbers, just
          written down differently.  Don't be alarmed if a future
          version of rrdtool displays a slightly different form of
          output. The examples in this document are correct for
          version 1.2.0 of RRDtool.

          The meaning of the above output will become clear below.

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

          This will create speed.png which starts at 12:00 and ends at
          13:00.  There is a definition of a variable called myspeed,
          using the data from RRA "speed" out of database "test.rrd".
          The line drawn is 2 pixels high and represents the variable
          myspeed. The color is red (specified by its
          rgb-representation, see below).

          You'll notice that the start of the graph is not at 12:00



     Page 7                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          but at 12:05.  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)

          Additionally you can add an alpha channel (transparency).
          The default will be "FF" which means non-transparent.

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

          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.
          Sometimes a label doesn't fit (12:00 and 13:00 would be
          candidates) 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
          (12'357-12'345) and divided by 300 this makes 0.04, which is
          displayed by RRDtool as "40 m" meaning "40/1'000". The "m"
          (milli) has nothing to do with meters, kilometers or
          millimeters! RRDtool doesn't know about the physical units
          of our data, it just works with dimensionless numbers.

          If we had measured our distances in meters, this would have
          been (12'357'000-12'345'000)/300 = 12'000/300 = 40.

          As most people have a better feel for numbers in this range,
          we'll correct that. We could recreate our database and store
          the correct data, but there is a better way: we do some
          calculations while creating the png file!





     Page 8                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



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

          Note: Make sure not to forget the backslash \ in front of
          the multiplication operator * above. The backslash is needed
          to "escape" the * as some operating systems might interpret
          and expand * instead of passing it to the rrdtool command.

          After viewing this PNG, you notice the "m" (milli) 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 PNG should look the same.

          The calculations are specified in the CDEF part above and
          are in Reverse Polish Notation ("RPN"). What we requested
          RRDtool to do 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 1'000, 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 * 3'600
           Calculate kilometers per hour: value / 1'000
           Together this makes:           value * (3'600/1'000) or value * 3.6

          In our example database we made a mistake and we need to
          compensate for this by multiplying with 1'000. Applying that
          correction:

           value * 3.6  * 1'000 == value * 3'600

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













     Page 9                                          (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



           rrdtool graph speed3.png                             \
                --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"

          Note: here we use another means to escape the * operator by
          enclosing the whole string in double quotes.

          This graph looks much better. Speed is shown in KM/H and
          there is even an extra line with the maximum allowed speed
          (on the road I travel on). 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 speed
          measurements within the speed limit 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 values above the speed limit:

             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 PNG:

             rrdtool graph speed4.png                           \
                --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 the three
          PNGs:




     Page 10                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



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

          Name the file "speed.html" or similar, and look at it in
          your web browser.

          Now, all you have to do is measure the values regularly and
          update the database.  When you want to view the data,
          recreate the PNGs and make sure to refresh them in your
          browser. (Note: just clicking reload may not be enough,
          especially when proxies are involved.  Try shift-reload or
          ctrl-F5).

          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 specify the current time by filling in
          a "N" as the time.  Or you could use the "time" function in
          Perl (the shortest example in this tutorial):

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

          How to run a program on regular intervals is OS specific.
          But here is an example in pseudo code:

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

          (do not try this with our test database, we'll use it in
          further examples)

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

          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 that 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, for
          example, the cups of 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 so far. Later on we will also be able to



     Page 11                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          monitor other types of values like temperature.

          Most (?) people interested in RRDtool will use the counter
          that keeps track of octets (bytes) transfered by a network
          device. So let's do just that next. We will start with a
          description of how to collect data.

          Some people will make a remark that there are tools which
          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 networked equipment. The
          tool I use below is called "snmpget" and this is how it
          works:

             snmpget device password OID

          or

             snmpget -v[version] -c[password] device 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 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 the above part of OIDs as a



     Page 12                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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 ...

          Ok, 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 (e.g., 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 the sources
          yourself and compile those.  The Internet is full of
          sources, programs etc. Find information using a search
          engine or whatever you prefer.

          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 give an example which can be used on Fedora Core 3.
          If it doesn't work for you, work your way through the manual
          of snmp and adapt the example to make it work.

             snmpget -v2c -c public myrouter system.sysDescr.0

          The device should answer with a description of itself,
          perhaps an empty one. 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 -v2c -c public myrouter 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 -v2c -c public myrouter 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 -v2c -c public cisco
          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"



     Page 13                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



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

             [user@host /home/alex]$ snmpget -v2c -c public cisco 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

             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 the above section 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 which stores about the
          following amount of data:






     Page 14                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



           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
          stored in the database 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)

             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 to collect data and store it. Here is an
          example.  It is written partially in pseudo code,  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:



     Page 15                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



             rrdtool graph myrouter-day.png --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=86'400, we start at now minus 86'400 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 to work.

          Suggestion: 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 and 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 many
          KM you had traveled, the averaged picture would be the right
          one to look at. On the other hand, for the speed that we
          traveled at, the maximum numbers seen is much more
          interesting. 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



     Page 16                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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 working days, and maxima of 120 KM/H (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 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.
          However, it probably 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. 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 highways 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 a lot of data over a longer period of
          time. Therefore we average it, eventually to one value per
          day. From this one value, we cannot see much detail, of
          course.

          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 ana appropriate
          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 didn't have the graph at all.

          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 know how to create a database and can put data in it.
          You can get the numbers out again by creating an image, do
          math on the data from the database and view the resulte
          instead of the raw data.  You know about the difference



     Page 17                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          between averages and maxima, and when to use which (or at
          least you should 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 tutorial, 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
          explanations.

          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 computer room is
          probably 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 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 air conditioned) -> 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 additional 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.



     Page 18                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          Example: our first example (12'345, 12'357, 12'363, 12'363)
          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.png -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"

          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 type, so it should continuously
            increment and RRDtool must 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 of type DERIVE. It should be a counter that can
            decrease. It does so between 2'400 and 0, with 1'800
            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.




     Page 19                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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 PNG shows all this, you know you have entered the
          data correctly, 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 is 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, right? 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
            they are.

          +o Line C: Again, the start-out value is unknown. The same
            story is holds as for line A. In this case the deltas are
            not constant, therefore the line is not either. 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 this makes a difference.

          +o Line D: Here the device calculates the deltas. Therefore
            we DO know the first delta and it is plotted. We had the
            same input as with line A, but the meaning of this input
            is different and thus 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 values.







     Page 20                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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 the
          counter shows 999'987. We travel 20 KM and the counter
          should go to 1'000'007. Unfortunately, there are only six
          digits on our counter so it really shows 000'007. If we
          would plot that on a type DERIVE, it would mean that the
          counter was set back 999'980 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 - 999'987 = -999'980    (instead of 1'000'007-999'987=20)

           Real delta = -999'980 + 999'999 + 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 ..           4'294'967'295
           - 64 bits: 0 .. 18'446'744'073'709'551'615

          If these numbers look strange to you, you can 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 erroneously added small value.

          There is a risk in this: suppose the large counter wrapped
          while adding a huge delta, it could happen, theoretically,
          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 worth thinking about. Even though, I did
          include an example, so you can judge for yourself.




     Page 21                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          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: (4'294'967'295 + 1) =                                4'294'967'296
           - 64 bits: (18'446'744'073'709'551'615 + 1)
                                              - correction1 = 18'446'744'069'414'584'320

           Before:        4'294'967'200
           Increase:                100
           Should become: 4'294'967'300
           But really is:             4
           Delta:        -4'294'967'196
           Correction1:  -4'294'967'196 + 4'294'967'296 = 100

           Before:        18'446'744'073'709'551'000
           Increase:                             800
           Should become: 18'446'744'073'709'551'800
           But really is:                        184
           Delta:        -18'446'744'073'709'550'816
           Correction1:  -18'446'744'073'709'550'816
                                          + 4'294'967'296 = -18'446'744'069'414'583'520
           Correction2:  -18'446'744'069'414'583'520
                             + 18'446'744'069'414'584'320 = 800

           Before:        18'446'744'073'709'551'615 ( maximum value )
           Increase:      18'446'744'069'414'584'320 ( absurd increase, minimum for
           Should become: 36'893'488'143'124'135'935             this example to work )
           But really is: 18'446'744'069'414'584'319
           Delta:                     -4'294'967'296
           Correction1:  -4'294'967'296 + 4'294'967'296 = 0
           (not negative -> no correction2)

           Before:        18'446'744'073'709'551'615 ( maximum value )
           Increase:      18'446'744'069'414'584'319 ( one less increase )
           Should become: 36'893'488'143'124'135'934
           But really is: 18'446'744'069'414'584'318
           Delta:                     -4'294'967'297
           Correction1:  -4'294'967'297 + 4'294'967'296 = -1
           Correction2:  -1 + 18'446'744'069'414'584'320 = 18'446'744'069'414'584'319

          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 values. Until now, we
          used "U", meaning "unknown". If you provide values for one



     Page 22                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          or both of them and if RRDtool receives data points 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 set it to 10, where as the maximum
          temperature I would set to 80. Any higher and the device
          would be out of order.

          For the speed of my car, I would never expect negative
          numbers and also I would not expect a speed  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 suspicion if it seems weird
          to you.

          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 data and feed it into
          RRDtool on exact intervals. RRDtool therefore interpolates
          the data, so they are stored 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 by 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 by 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 by 297. Again,
          RRDtool interpolates and stores 300 as it should be.

                in the RRD                 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 920'805'000 to 920'805'900 as this goes very well with
          the example numbers.






     Page 23                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



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

          Make a copy

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

          Put in some data

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

          Create output

             rrdtool graph seconds1.png                       \
                --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.png                       \
                --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

          View both images together (add them to your index.html file)
          and compare. Both graphs should show the same, despite the
          input being different.

     WWWWRRRRAAAAPPPPUUUUPPPP
          It's time now to wrap up this tutorial. We covered all the
          basics for you to be able to work with RRDtool and to read
          the additional documentation available. There is plenty more
          to discover about RRDtool and you will find more and more
          uses for this package. You can easly create graphs using
          just the examples provided and using only RRDtool. You can
          also use one of the front ends to RRDtool 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



     Page 24                                         (printed 6/13/06)






     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....2222....11113333 ((((2222000000006666----00005555----00004444))))         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))))



          Remember to subscribe to the RRDtool mailing list. Even if
          you are not answering to mails that come by, it helps both
          you and the rest of the users. 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

     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 answers, but at the same time learn a whole lot more.

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


































     Page 25                                         (printed 6/13/06)



