


rrdtool                                            RRDTUTORIAL(1)



NNNNAAAAMMMMEEEE
     rrdtutorial - Alex van den Bogaerdt's RRDtool tutorial

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     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.

TTTTUUUUTTTTOOOORRRRIIIIAAAALLLL
     IIIImmmmppppoooorrrrttttaaaannnntttt

     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.

     WWWWhhhhaaaatttt iiiissss RRRRRRRRDDDDttttoooooooollll ????

     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.

     WWWWhhhhaaaatttt ddddaaaattttaaaa ccccaaaannnn bbbbeeee ppppuuuutttt iiiinnnnttttoooo aaaannnn RRRRDDDDDDDD ????

     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



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rrdtool                                            RRDTUTORIAL(1)



     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 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.

     WWWWhhhhaaaatttt ccccaaaannnn IIII ddddoooo wwwwiiiitttthhhh tttthhhhiiiissss ttttoooooooollll ????

     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.

     WWWWhhhhaaaatttt iiiiffff IIII ssssttttiiiillllllll hhhhaaaavvvveeee pppprrrroooobbbblllleeeemmmmssss aaaafffftttteeeerrrr rrrreeeeaaaaddddiiiinnnngggg tttthhhhiiiissss ddddooooccccuuuummmmeeeennnntttt ????

     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-



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rrdtool                                            RRDTUTORIAL(1)



     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".

     HHHHoooowwww wwwwiiiillllllll yyyyoooouuuu hhhheeeellllpppp mmmmeeee ????

     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 the bin_dec_hex manpage
     before you continue here.

     YYYYoooouuuurrrr ffffiiiirrrrsssstttt RRRRoooouuuunnnndddd RRRRoooobbbbiiiinnnn DDDDaaaattttaaaabbbbaaaasssseeee

     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.



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rrdtool                                            RRDTUTORIAL(1)



     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

     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



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rrdtool                                            RRDTUTORIAL(1)



     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.

        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
     ...')

     WWWWhhhhaaaatttt hhhhaaaassss bbbbeeeeeeeennnn ccccrrrreeeeaaaatttteeeedddd ????

     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:











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rrdtool                                            RRDTUTORIAL(1)



      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 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











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rrdtool                                            RRDTUTORIAL(1)



      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.

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

     IIIItttt iiiissss ttttiiiimmmmeeee ttttoooo ccccrrrreeeeaaaatttteeee ssssoooommmmeeee ggggrrrraaaapppphhhhiiiiccccssss

     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



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rrdtool                                            RRDTUTORIAL(1)



     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"

     GGGGrrrraaaapppphhhhiiiiccccssss wwwwiiiitttthhhh ssssoooommmmeeee mmmmaaaatttthhhh

     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 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



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rrdtool                                            RRDTUTORIAL(1)



     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 ...

        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








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rrdtool                                            RRDTUTORIAL(1)



     GGGGrrrraaaapppphhhhiiiiccccssss MMMMaaaaggggiiiicccc

     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:

        <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).

     UUUUppppddddaaaatttteeeessss iiiinnnn RRRReeeeaaaalllliiiittttyyyy

     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:





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rrdtool                                            RRDTUTORIAL(1)



        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

     SSSSoooommmmeeee wwwwoooorrrrddddssss oooonnnn SSSSNNNNMMMMPPPP

     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 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



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rrdtool                                            RRDTUTORIAL(1)



     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.  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.





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rrdtool                                            RRDTUTORIAL(1)



        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

        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.







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rrdtool                                            RRDTUTORIAL(1)



     AAAA RRRReeeeaaaallll WWWWoooorrrrlllldddd EEEExxxxaaaammmmpppplllleeee

     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)

        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



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rrdtool                                            RRDTUTORIAL(1)



     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:

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

     CCCCoooonnnnssssoooolllliiiiddddaaaattttiiiioooonnnn FFFFuuuunnnnccccttttiiiioooonnnnssss

     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



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rrdtool                                            RRDTUTORIAL(1)



     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. 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



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rrdtool                                            RRDTUTORIAL(1)



     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.

     LLLLeeeetttt''''ssss rrrreeeevvvviiiieeeewwww wwwwhhhhaaaatttt yyyyoooouuuu nnnnoooowwww sssshhhhoooouuuulllldddd kkkknnnnoooowwww....

     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.

     DDDDaaaattttaaaa SSSSoooouuuurrrrcccceeee TTTTyyyyppppeeeessss

     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 rather constant value. I know when
     the router is busy (it works -> it uses more electricity ->



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rrdtool                                            RRDTUTORIAL(1)



     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"







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rrdtool                                            RRDTUTORIAL(1)



     RRRRRRRRDDDDttttoooooooollll uuuunnnnddddeeeerrrr tttthhhheeee MMMMiiiiccccrrrroooossssccccooooppppeeee

     +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



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rrdtool                                            RRDTUTORIAL(1)



       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 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.

     CCCCoooouuuunnnntttteeeerrrr WWWWrrrraaaappppssss

     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



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rrdtool                                            RRDTUTORIAL(1)



     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 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




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rrdtool                                            RRDTUTORIAL(1)



     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 "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.

     DDDDaaaattttaaaa RRRReeeessssaaaammmmpppplllliiiinnnngggg

     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



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rrdtool                                            RRDTUTORIAL(1)



     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

        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.

WWWWRRRRAAAAPPPPUUUUPPPP
     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.

MMMMAAAAIIIILLLLIIIINNNNGGGGLLLLIIIISSSSTTTT
     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



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rrdtool                                            RRDTUTORIAL(1)



     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.

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     The RRDtool manpages

AAAAUUUUTTTTHHHHOOOORRRR
     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>







































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