RRDTUTORIAL(1)                      RRDtool                     RRDTUTORIAL(1)



NNAAMMEE
       rrdtutorial - Alex van den Bogaerdt's RRDTool tutorial

DDEESSCCRRIIPPTTIIOONN
       RRDTool is written by Tobias Oetiker <oetiker@ee.ethz.ch> with contri-
       butions from many people all around the world. This document is written
       by Alex van den Bogaerdt <alex@ergens.op.het.net> to help you under-
       stand 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 RRD-
       Tool. It should prepare you to read the documentation yourself.  It
       also explains the general things about statistics with a focus on net-
       working.

TTUUTTOORRIIAALL
       IImmppoorrttaanntt

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

       WWhhaatt iiss RRRRDDTTooooll ??

       RRDTool refers to Round Robin Database tool.  Round robin is a tech-
       nique that works with a fixed amount of data, and a pointer to the cur-
       rent 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 ele-
       ment. 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 maintenance.  RRDTool
       works with with Round Robin Databases (RRDs). It stores and retrieves
       data from them.

       WWhhaatt ddaattaa ccaann bbee ppuutt iinnttoo aann RRRRDD ??

       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 RRD-
       Tool. 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, inte-
       gers.

       Many examples talk about SNMP which is an acronym for Simple Network
       Management Protocol. "Simple" refers to the protocol -- it does not
       mean it is simple to manage or monitor a network. After working your
       way through this document, you should know enough to be able to under-
       stand 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.

       WWhhaatt ccaann II ddoo wwiitthh tthhiiss ttooooll ??

       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 pro-
       cess 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 con-
       sumption, 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.

       WWhhaatt iiff II ssttiillll hhaavvee pprroobblleemmss aafftteerr rreeaaddiinngg tthhiiss ddooccuummeenntt ??

       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 ques-
       tion 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 sub-
       ject 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".

       HHooww wwiillll yyoouu hheellpp mmee ??

       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 exam-
       ples you get some hands-on experience and, even more important, some
       background information of how it works.

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

       YYoouurr ffiirrsstt RRoouunndd RRoobbiinn DDaattaabbaassee

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

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

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

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

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

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

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

       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 exam-
       ple at home or where I live :)

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

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

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

          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 ...")

       WWhhaatt hhaass bbeeeenn ccrreeaatteedd ??

       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 (e.g. there's nothing to average) and keeps
       24 samples (24 times 5 minutes is 2 hours). The other averages 6 values
       (half hour) and contains 10 of such averages (e.g. 5 hours) The remain-
       ing options will be discussed later on.

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

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

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

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

       We fill the database as follows:

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

       This reads: update our test database with the following numbers

        time 920804700, value 12345
        time 920805000, value 12357

       etcetera.

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

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

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

       It should return the following output:

                       speed

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

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

       What this output represents will become clear in the rest of the tuto-
       rial.

       IItt iiss ttiimmee ttoo ccrreeaattee ssoommee ggrraapphhiiccss

       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 com-
       ponents, you specify how much to use in hexadecimal where 00 means not
       included and FF means fully included.  The "color" white is a mixture
       of red, green and blue: FFFFFF The "color" black is all colors off:
       000000

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

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

       GGrraapphhiiccss wwiitthh ssoommee mmaatthh

       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! RRD-
       Tool 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 cor-
       rect data but there is a better way: do some calculations while creat-
       ing 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 Nota-
       tion ("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 tuto-
       rial 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 possi-
       ble 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

       GGrraapphhiiccss MMaaggiicc

       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).

       UUppddaatteess iinn RReeaalliittyy

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

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

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

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

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

       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

       SSoommee wwoorrddss oonn SSNNMMPP

       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 moni-
       tored 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, how-
       ever this can be disabled, altered or protected for privacy and secu-
       rity reasons.  Read the documentation that comes with your device or
       program.

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

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

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

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

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

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

          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" inter-
       face 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 for-
       get 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, con-
       tinue on with this tutorial. If not, then go back and re-read this
       part.

       AA RReeaall WWoorrlldd EExxaammppllee

       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 approxi-
       mately 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 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.

       CCoonnssoolliiddaattiioonn FFuunnccttiioonnss

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

       Recall all the stuff about the speed of the car. Suppose we drove at
       144 KM/H during 5 minutes and then were stopped by the police for 25
       minutes.  At the end of the lecture we would take our laptop and cre-
       ate+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 sam-
       ples measured would be 144+0+0+0+0+0=144, divided by 30 minutes, cor-
       rected 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 max-
       ima will have higher numbers.  For my car this would translate in aver-
       ages 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 dis-
       tances 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 sec-
       ond 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 mea-
       sured every 300 seconds).  You would be able to see when I stopped,
       when I was in top gear, when I drove over fast highways etc. The granu-
       larity 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, even-
       tually to one value per day. From this one value, we cannot see much
       detail.

       Make sure you understand the last few paragraphs. There is no value in
       only a line and a few axis, you need to know what they mean and inter-
       pret 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 some-
       thing that it is not suitable for. You would be better off if you would
       not have the graphics at all in that case.

       LLeett''ss rreevviieeww wwhhaatt yyoouu nnooww sshhoouulldd kknnooww..

       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 monitor-
       ing long after you read this introduction.

       DDaattaa SSoouurrccee TTyyppeess

       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 possi-
       bilities.  For instance, I'm able to retrieve the temperature from my
       router in three places namely the inlet, the so called hot-spot and the
       exhaust.  These values are not counters.  If I take the difference of
       the two samples and divide that by 300 seconds I would be asking for
       the temperature change per second.  Hopefully this is zero! If not, the
       computer room is on fire :)

       So, what can we do ?  We can tell RRDTool to store the values we mea-
       sure 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 con-
       stant 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 tem-
       perature rises) etc. The data type we use when creating the database
       before was counter, we now have a different data type and thus a dif-
       ferent 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"

       RRRRDDTTooooll uunnddeerr tthhee MMiiccrroossccooppee


       ? 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).

       ? 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 in-between.

       ? Line D is of type absolute. This is like counter but it works on val-
         ues 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:

       ? 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 !

       ? 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.

       CCoouunntteerr WWrraappss

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

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

        Real delta = -999980 + 999999 + 1 = 20

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

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

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

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

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

       Correction numbers:

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

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

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

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

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

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

       DDaattaa RReessaammpplliinngg

       One important feature of RRDTool has not been explained yet: It is vir-
       tually 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 RRD                 in reality

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

       Let's create two identical databases. I've chosen the time range
       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.

WWRRAAPPUUPP
       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.

MMAAIILLIINNGGLLIISSTT
       Remember to subscribe to the mailing-list. Even if you are not answer-
       ing 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.

SSEEEE AALLSSOO
       The RRDTool manpages

AAUUTTHHOORR
       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>



1.0.49                            2004-04-24                    RRDTUTORIAL(1)
