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       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 RRD­
       tool is and what it can do for you.

       The documentation provided with RRDtool can be too techni­
       cal 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 network­



       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.

       What is RRDtool ?

       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 begin­
       ning nor an end, you can go on and on. After a while, all
       the available places will be used and the process automat­
       ically 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.

       What data can be put into an RDD ?

       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 Sim­
       ple 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
       ture, 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 depen­
       dent 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 visi­
       tors at an exhibition, noise levels near an airport, tem­
       perature 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.

       What if I still have problems after reading this document

       First of all: read it again! You may have missed some­
       thing.  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 consid­
       ered rude to just ask a question without searching the
       archives: your problem may already have been solved for
       somebody else!  This is true for most, if not all, mailing
       lists and not only for this particular list! Look in the
       documentation that came with RRDtool for the location and
       usage of the list.

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

       How will you help me ?

       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
       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

       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 val­
       ues 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 calcu­

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

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

       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 automo­
       bile 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 abbrevia­

        M:    meter
        KM:   kilometer (= 1000 meters).

       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 con­
       stant speed.  There is an example later on in this tuto­
       rial that explains this.

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

       We will now create a database where we can keep all these
       interesting numbers. The method used to start the program
       may differ slightly from OS to OS but I assume you can
       figure it out if it works different on your OS. Make sure
       you do not overwrite any file on your system when execut­
       ing 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       \

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

       What has been created ?

       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
       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

        time 920804700, value 12345
        time 920805000, value 12357


       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 "rrd­
       tool fetch":

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

       It should return the following output:


        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.

       It is time to create some graphics

       Try the following command:

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

       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 hexadec­
       imal 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:

          red     #FF0000
          green   #00FF00

       plays 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

       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,*                   \

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

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

       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

             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

       Graphics Magic

       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

          <IMG src="speed2.gif" alt="Speed in meters per second">
          <IMG src="speed3.gif" alt="Speed in kilometers per hour">
          <IMG src="speed4.gif" alt="Traveled too fast?">

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

       "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 spe­
       cific. But here's an example in pseudo code:

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

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

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

       Some words on SNMP

       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 moni­
       tor 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!  How­
       ever, 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
       also be written down as numbers and are 1 3 6 1 2 1.

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

       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 spec­
       ify 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 From there, we are especially interested in
       the branch "interfaces" which has number 2 (eg or

       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, pre­
       fix with . 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 differ­
       ent device, there is no point in continuing.

          snmpget myrouter public interfaces.ifNumber.0

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

          snmpwalk myrouter public interfaces.ifTable.ifEntry.ifDescr

       ernet0" interface and see that it is number four. I try:

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

          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):


       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 descrip­
       tive text... At least, when people are talking about MIBs
       and OIDs you know what it's all about.  Do not forget the
       interface number (0 if it is not interface dependent) and
       try snmpwalk if you don't get an answer from snmpget.

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

       A Real World Example

       Let the fun begin. First, create a new database. It con­
       tains 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

          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         \

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

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

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

             wait for 5 minutes

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

       Obviously, in this case, we shouldn't look at the aver­
       ages. 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 maxi­
       mum of 120 KM/H on weekdays (my top speed that I reach
       every day).

       Big difference. Do not look at the second graph to esti­
       mate 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 Aus­
       tria 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
       that case.

       Let's review what you now should know.

       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 every­
       thing. It will be worth the effort and helps you not only
       with the rest of this doc but also in your day to day mon­
       itoring long after you read this introduction.

       Data Source Types

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

       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 exam­
       ples 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 -> 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

       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 \
          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  \
          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"

       RRDtool under the Microscope

       · Line A is a counter so it should continuously increment
         and RRDtool should calculate the differences. Also, RRD­
         tool 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).

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

       · Line C is derive. It should be a counter that can
         decrease. It does so between 2400 and 0, with 1800

       · 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

        - Line A:  u  u  1  1  1  1  1  1  1  1  1  u
         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 calcu­
         late 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 !

       · Line B: There is nothing to calculate. The numbers are
         as is.

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

       · 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.

       Counter Wraps

       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 maxi­
       mum 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:
       that wrapped. Add the maximum possible value of the large
       counter + 1 and subtract the falsely added small value.
       There is a risk in this: suppose the large counter wrapped
       while adding a huge delta, it could happen in theory that
       adding the smaller value would make the delta positive. In
       this unlikely case the results would not be correct. The
       increase should be nearly as high as the maximum counter
       value for that to happen so chances are you would have
       several other problems as well and this particular problem
       would not even be worth thinking about. Even though I did
       include an example of it so you can judge that for your­

       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 num­
       bers :)

       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

       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.

       Data Resampling

       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 sec­
       onds late and the interval is 303. The delta will also be
       303 in that case. Obviously RRDtool should not put 303 in
       the database and make you believe that the counter
       increased 303 in 300 seconds.  This is where RRDtool
       interpolates: it alters the 303 value as if it would have
       been stored earlier and it will be 300 in 300 seconds.
       Next time you are at exactly the right time. This means
       that the current interval is 297 seconds and also the
       counter increased with 297. Again RRDtool alters the value
       and stores 300 as it should be.

             in the RDD                 in reality

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

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

          rrdtool create seconds1.rrd   \
             --start 920804700          \
             DS:seconds:COUNTER:600:U:U \

          for Unix: cp seconds1.rrd seconds2.rrd
             LINE2:seconds#0000FF                          \
          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                          \

       Both graphs should show the same.


       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.


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


       The RRDtool manpages


       I hope you enjoyed the examples and their descriptions. If
       you do, help other people by pointing them to this docu­
       ment 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>

1.0.45                      2003-02-27             RRDTUTORIAL(1)
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