1RRDTUTORIAL(1)                      rrdtool                     RRDTUTORIAL(1)
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NAME

6       rrdtutorial - Alex van den Bogaerdt's RRDtool tutorial
7

DESCRIPTION

9       RRDtool is written by Tobias Oetiker <tobi@oetiker.ch> with
10       contributions from many people all around the world. This document is
11       written by Alex van den Bogaerdt <alex@vandenbogaerdt.nl> to help you
12       understand what RRDtool is and what it can do for you.
13
14       The documentation provided with RRDtool can be too technical for some
15       people. This tutorial is here to help you understand the basics of
16       RRDtool. It should prepare you to read the documentation yourself.  It
17       also explains the general things about statistics with a focus on
18       networking.
19

TUTORIAL

21   Important
22       Please don't skip ahead in this document!  The first part of this
23       document explains the basics and may be boring.  But if you don't
24       understand the basics, the examples will not be as meaningful to you.
25
26       Sometimes things change.  This example used to provide numbers like
27       "0.04" instead of "4.00000e-02".  Those are really the same numbers,
28       just written down differently.  Don't be alarmed if a future version of
29       rrdtool displays a slightly different form of output. The examples in
30       this document are correct for version 1.2.0 of RRDtool.
31
32       Also, sometimes bugs do occur. They may also influence the outcome of
33       the examples. Example speed4.png was suffering from this (the handling
34       of unknown data in an if-statement was wrong). Normal data will be just
35       fine (a bug in rrdtool wouldn't last long) but special cases like NaN,
36       INF and so on may last a bit longer.  Try another version if you can,
37       or just live with it.
38
39       I fixed the speed4.png example (and added a note). There may be other
40       examples which suffer from the same or a similar bug.  Try to fix it
41       yourself, which is a great exercise. But please do not submit your
42       result as a fix to the source of this document. Discuss it on the
43       user's list, or write to me.
44
45   What is RRDtool?
46       RRDtool refers to Round Robin Database tool.  Round robin is a
47       technique that works with a fixed amount of data, and a pointer to the
48       current element. Think of a circle with some dots plotted on the edge.
49       These dots are the places where data can be stored. Draw an arrow from
50       the center of the circle to one of the dots; this is the pointer.  When
51       the current data is read or written, the pointer moves to the next
52       element. As we are on a circle there is neither a beginning nor an end,
53       you can go on and on and on. After a while, all the available places
54       will be used and the process automatically reuses old locations. This
55       way, the dataset will not grow in size and therefore requires no
56       maintenance.  RRDtool works with Round Robin Databases (RRDs). It
57       stores and retrieves data from them.
58
59   What data can be put into an RRD?
60       You name it, it will probably fit as long as it is some sort of time-
61       series data. This means you have to be able to measure some value at
62       several points in time and provide this information to RRDtool. If you
63       can do this, RRDtool will be able to store it. The values must be
64       numerical but don't have to be integers, as is the case with MRTG (the
65       next section will give more details on this more specialized
66       application).
67
68       Many examples below talk about SNMP which is an acronym for Simple
69       Network Management Protocol. "Simple" refers to the protocol. It does
70       not mean it is simple to manage or monitor a network. After working
71       your way through this document, you should know enough to be able to
72       understand what people are talking about. For now, just realize that
73       SNMP can be used to query devices for the values of counters they keep.
74       It is the value from those counters that we want to store in the RRD.
75
76   What can I do with this tool?
77       RRDtool originated from MRTG (Multi Router Traffic Grapher). MRTG
78       started as a tiny little script for graphing the use of a university's
79       connection to the Internet. MRTG was later (ab-)used as a tool for
80       graphing other data sources including temperature, speed, voltage,
81       number of printouts and the like.
82
83       Most likely you will start to use RRDtool to store and process data
84       collected via SNMP. The data will most likely be bytes (or bits)
85       transferred from and to a network or a computer.  But it can also be
86       used to display tidal waves, solar radiation, power consumption, number
87       of visitors at an exhibition, noise levels near an airport, temperature
88       on your favorite holiday location, temperature in the fridge and
89       whatever your imagination can come up with.
90
91       You only need a sensor to measure the data and be able to feed the
92       numbers into RRDtool. RRDtool then lets you create a database, store
93       data in it, retrieve that data and create graphs in PNG format for
94       display on a web browser. Those PNG images are dependent on the data
95       you collected and could be, for instance, an overview of the average
96       network usage, or the peaks that occurred.
97
98   What if I still have problems after reading this document?
99       First of all: read it again! You may have missed something.  If you are
100       unable to compile the sources and you have a fairly common OS, it will
101       probably not be the fault of RRDtool. There may be pre-compiled
102       versions around on the Internet. If they come from trusted sources, get
103       one of those.
104
105       If on the other hand the program works but does not give you the
106       expected results, it will be a problem with configuring it. Review your
107       configuration and compare it with the examples that follow.
108
109       There is a mailing list and an archive of it. Read the list for a few
110       weeks and search the archive. It is considered rude to just ask a
111       question without searching the archives: your problem may already have
112       been solved for somebody else!  This is true for most, if not all,
113       mailing lists and not only for this particular one. Look in the
114       documentation that came with RRDtool for the location and usage of the
115       list.
116
117       I suggest you take a moment to subscribe to the mailing list right now
118       by sending an email to <rrd-users-request@lists.oetiker.ch> with a
119       subject of "subscribe". If you ever want to leave this list, just write
120       an email to the same address but now with a subject of "unsubscribe".
121
122   How will you help me?
123       By giving you some detailed descriptions with detailed examples.  I
124       assume that following the instructions in the order presented will give
125       you enough knowledge of RRDtool to experiment for yourself.  If it
126       doesn't work the first time, don't give up. Reread the stuff that you
127       did understand, you may have missed something.
128
129       By following the examples you get some hands-on experience and, even
130       more important, some background information of how it works.
131
132       You will need to know something about hexadecimal numbers. If you
133       don't, start with reading bin_dec_hex before you continue here.
134
135   Your first Round Robin Database
136       In my opinion the best way to learn something is to actually do it.
137       Why not start right now?  We will create a database, put some values in
138       it and extract this data again.  Your output should be the same as the
139       output that is included in this document.
140
141       We will start with some easy stuff and compare a car with a router, or
142       compare kilometers (miles if you wish) with bits and bytes. It's all
143       the same: some number over some time.
144
145       Assume we have a device that transfers bytes to and from the Internet.
146       This device keeps a counter that starts at zero when it is turned on,
147       increasing with every byte that is transferred. This counter will
148       probably have a maximum value. If this value is reached and an extra
149       byte is counted, the counter starts over at zero. This is the same as
150       many counters in the world such as the mileage counter in a car.
151
152       Most discussions about networking talk about bits per second so let's
153       get used to that right away. Assume a byte is eight bits and start to
154       think in bits not bytes. The counter, however, still counts bytes!  In
155       the SNMP world most of the counters are 32 bits. That means they are
156       counting from 0 to 4294967295. We will use these values in the
157       examples.  The device, when asked, returns the current value of the
158       counter. We know the time that has passes since we last asked so we now
159       know how many bytes have been transferred ***on average*** per second.
160       This is not very hard to calculate. First in words, then in
161       calculations:
162
163       1. Take the current counter, subtract the previous value from it.
164
165       2. Do the same with the current time and the previous time (in
166          seconds).
167
168       3. Divide the outcome of (1) by the outcome of (2), the result is the
169          amount of bytes per second. Multiply by eight to get the number of
170          bits per second (bps).
171
172         bps = (counter_now - counter_before) / (time_now - time_before) * 8
173
174       For some people it may help to translate this to an automobile example.
175       Do not try this example, and if you do, don't blame me for the results!
176
177       People who are not used to think in kilometers per hour can translate
178       most into miles per hour by dividing km by 1.6 (close enough).  I will
179       use the following abbreviations:
180
181        m:    meter
182        km:   kilometer (= 1000 meters).
183        h:    hour
184        s:    second
185        km/h: kilometers per hour
186        m/s:  meters per second
187
188       You are driving a car. At 12:05 you read the counter in the dashboard
189       and it tells you that the car has moved 12345 km until that moment.  At
190       12:10 you look again, it reads 12357 km. This means you have traveled
191       12 km in five minutes. A scientist would translate that into meters per
192       second and this makes a nice comparison toward the problem of (bytes
193       per five minutes) versus (bits per second).
194
195       We traveled 12 kilometers which is 12000 meters. We did that in five
196       minutes or 300 seconds. Our speed is 12000m / 300s or 40 m/s.
197
198       We could also calculate the speed in km/h: 12 times 5 minutes is an
199       hour, so we have to multiply 12 km by 12 to get 144 km/h.  For our
200       native English speaking friends: that's 90 mph so don't try this
201       example at home or where I live :)
202
203       Remember: these numbers are averages only.  There is no way to figure
204       out from the numbers, if you drove at a constant speed.  There is an
205       example later on in this tutorial that explains this.
206
207       I hope you understand that there is no difference in calculating m/s or
208       bps; only the way we collect the data is different. Even the k from
209       kilo is the same as in networking terms k also means 1000.
210
211       We will now create a database where we can keep all these interesting
212       numbers. The method used to start the program may differ slightly from
213       OS to OS, but I assume you can figure it out if it works different on
214       yours. Make sure you do not overwrite any file on your system when
215       executing the following command and type the whole line as one long
216       line (I had to split it for readability) and skip all of the '\'
217       characters.
218
219          rrdtool create test.rrd             \
220                   --start 920804400          \
221                   DS:speed:COUNTER:600:U:U   \
222                   RRA:AVERAGE:0.5:1:24       \
223                   RRA:AVERAGE:0.5:6:10
224
225       (So enter: "rrdtool create test.rrd --start 920804400 DS ...")
226
227   What has been created?
228       We created the round robin database called test (test.rrd) which starts
229       at noon the day I started writing this document, 7th of March, 1999
230       (this date translates to 920804400 seconds as explained below). Our
231       database holds one data source (DS) named "speed" that represents a
232       counter. This counter is read every five minutes (this is the default
233       therefore you don't have to put "--step=300").  In the same database
234       two round robin archives (RRAs) are kept, one averages the data every
235       time it is read (i.e., there's nothing to average) and keeps 24 samples
236       (24 times 5 minutes is 2 hours). The other averages 6 values (half
237       hour) and contains 10 such averages (e.g. 5 hours).
238
239       RRDtool works with special time stamps coming from the UNIX world.
240       This time stamp is the number of seconds that passed since January 1st
241       1970 UTC.  The time stamp value is translated into local time and it
242       will therefore look different for different time zones.
243
244       Chances are that you are not in the same part of the world as I am.
245       This means your time zone is different. In all examples where I talk
246       about time, the hours may be wrong for you. This has little effect on
247       the results of the examples, just correct the hours while reading.  As
248       an example: where I will see "12:05" the UK folks will see "11:05".
249
250       We now have to fill our database with some numbers. We'll pretend to
251       have read the following numbers:
252
253        12:05  12345 km
254        12:10  12357 km
255        12:15  12363 km
256        12:20  12363 km
257        12:25  12363 km
258        12:30  12373 km
259        12:35  12383 km
260        12:40  12393 km
261        12:45  12399 km
262        12:50  12405 km
263        12:55  12411 km
264        13:00  12415 km
265        13:05  12420 km
266        13:10  12422 km
267        13:15  12423 km
268
269       We fill the database as follows:
270
271        rrdtool update test.rrd 920804700:12345 920805000:12357 920805300:12363
272        rrdtool update test.rrd 920805600:12363 920805900:12363 920806200:12373
273        rrdtool update test.rrd 920806500:12383 920806800:12393 920807100:12399
274        rrdtool update test.rrd 920807400:12405 920807700:12411 920808000:12415
275        rrdtool update test.rrd 920808300:12420 920808600:12422 920808900:12423
276
277       This reads: update our test database with the following numbers
278
279        time 920804700, value 12345
280        time 920805000, value 12357
281
282       etcetera.
283
284       As you can see, it is possible to feed more than one value into the
285       database in one command. I had to stop at three for readability but the
286       real maximum per line is OS dependent.
287
288       We can now retrieve the data from our database using "rrdtool fetch":
289
290        rrdtool fetch test.rrd AVERAGE --start 920804400 --end 920809200
291
292       It should return the following output:
293
294                                 speed
295
296        920804700: nan
297        920805000: 4.0000000000e-02
298        920805300: 2.0000000000e-02
299        920805600: 0.0000000000e+00
300        920805900: 0.0000000000e+00
301        920806200: 3.3333333333e-02
302        920806500: 3.3333333333e-02
303        920806800: 3.3333333333e-02
304        920807100: 2.0000000000e-02
305        920807400: 2.0000000000e-02
306        920807700: 2.0000000000e-02
307        920808000: 1.3333333333e-02
308        920808300: 1.6666666667e-02
309        920808600: 6.6666666667e-03
310        920808900: 3.3333333333e-03
311        920809200: nan
312        920809500: nan
313
314       Note that you might get more rows than you expect. The reason for this
315       is that you ask for a time range that ends on 920809200. The number
316       that is written behind 920809200: in the list above covers the time
317       range from 920808900 to 920809200, EXCLUDING 920809200. Hence to be on
318       the sure side, you receive the entry from 920809200 to 920809500 as
319       well since it INCLUDES 920809200. You may also see "NaN" instead of
320       "nan" this is OS dependent.  "NaN" stands for "Not A Number".  If your
321       OS writes "U" or "UNKN" or something similar that's okay.  If something
322       else is wrong, it will probably be due to an error you made (assuming
323       that my tutorial is correct of course :-). In that case: delete the
324       database and try again.
325
326       The meaning of the above output will become clear below.
327
328   Time to create some graphics
329       Try the following command:
330
331        rrdtool graph speed.png                                 \
332                --start 920804400 --end 920808000               \
333                DEF:myspeed=test.rrd:speed:AVERAGE              \
334                LINE2:myspeed#FF0000
335
336       This will create speed.png which starts at 12:00 and ends at 13:00.
337       There is a definition of a variable called myspeed, using the data from
338       RRA "speed" out of database "test.rrd". The line drawn is 2 pixels high
339       and represents the variable myspeed. The color is red (specified by its
340       rgb-representation, see below).
341
342       You'll notice that the start of the graph is not at 12:00 but at 12:05.
343       This is because we have insufficient data to tell the average before
344       that time. This will only happen when you miss some samples, this will
345       not happen a lot, hopefully.
346
347       If this has worked: congratulations! If not, check what went wrong.
348
349       The colors are built up from red, green and blue. For each of the
350       components, you specify how much to use in hexadecimal where 00 means
351       not included and FF means fully included.  The "color" white is a
352       mixture of red, green and blue: FFFFFF The "color" black is all colors
353       off: 000000
354
355          red     #FF0000
356          green   #00FF00
357          blue    #0000FF
358          magenta #FF00FF     (mixed red with blue)
359          gray    #555555     (one third of all components)
360
361       Additionally you can (with a recent RRDtool)  add an alpha channel
362       (transparency).  The default will be "FF" which means non-transparent.
363
364       The PNG you just created can be displayed using your favorite image
365       viewer.  Web browsers will display the PNG via the URL
366       "file:///the/path/to/speed.png"
367
368   Graphics with some math
369       When looking at the image, you notice that the horizontal axis is
370       labeled 12:10, 12:20, 12:30, 12:40 and 12:50. Sometimes a label doesn't
371       fit (12:00 and 13:00 would be likely candidates) so they are skipped.
372
373       The vertical axis displays the range we entered. We provided kilometers
374       and when divided by 300 seconds, we get very small numbers. To be
375       exact, the first value was 12 (12357-12345) and divided by 300 this
376       makes 0.04, which is displayed by RRDtool as "40 m" meaning "40/1000".
377       The "m" (milli) has nothing to do with meters (also m), kilometers or
378       millimeters! RRDtool doesn't know about the physical units of our data,
379       it just works with dimensionless numbers.
380
381       If we had measured our distances in meters, this would have been
382       (12357000-12345000)/300 = 12000/300 = 40.
383
384       As most people have a better feel for numbers in this range, we'll
385       correct that. We could recreate our database and store the correct
386       data, but there is a better way: we do some calculations while creating
387       the png file!
388
389          rrdtool graph speed2.png                           \
390             --start 920804400 --end 920808000               \
391             --vertical-label m/s                            \
392             DEF:myspeed=test.rrd:speed:AVERAGE              \
393             CDEF:realspeed=myspeed,1000,\*                  \
394             LINE2:realspeed#FF0000
395
396       Note: I need to escape the multiplication operator * with a backslash.
397       If I don't, the operating system may interpret it and use it for file
398       name expansion. You could also place the line within quotation marks
399       like so:
400
401             "CDEF:realspeed=myspeed,1000,*"                  \
402
403       It boils down to: it is RRDtool which should see *, not your shell.
404       And it is your shell interpreting \, not RRDtool. You may need to
405       adjust examples accordingly if you happen to use an operating system or
406       shell which behaves differently.
407
408       After viewing this PNG, you notice the "m" (milli) has disappeared.
409       This is what the correct result would be. Also, a label has been added
410       to the image.  Apart from the things mentioned above, the PNG should
411       look the same.
412
413       The calculations are specified in the CDEF part above and are in
414       Reverse Polish Notation ("RPN"). What we requested RRDtool to do is:
415       "take the data source myspeed and the number 1000; multiply those".
416       Don't bother with RPN yet, it will be explained later on in more
417       detail. Also, you may want to read my tutorial on CDEFs and Steve
418       Rader's tutorial on RPN. But first finish this tutorial.
419
420       Hang on! If we can multiply values with 1000, it should also be
421       possible to display kilometers per hour from the same data!
422
423       To change a value that is measured in meters per second:
424
425        Calculate meters per hour:     value * 3600
426        Calculate kilometers per hour: value / 1000
427        Together this makes:           value * (3600/1000) or value * 3.6
428
429       In our example database we made a mistake and we need to compensate for
430       this by multiplying with 1000. Applying that correction:
431
432        value * 3.6  * 1000 == value * 3600
433
434       Now let's create this PNG, and add some more magic ...
435
436        rrdtool graph speed3.png                             \
437             --start 920804400 --end 920808000               \
438             --vertical-label km/h                           \
439             DEF:myspeed=test.rrd:speed:AVERAGE              \
440             "CDEF:kmh=myspeed,3600,*"                       \
441             CDEF:fast=kmh,100,GT,kmh,0,IF                   \
442             CDEF:good=kmh,100,GT,0,kmh,IF                   \
443             HRULE:100#0000FF:"Maximum allowed"              \
444             AREA:good#00FF00:"Good speed"                   \
445             AREA:fast#FF0000:"Too fast"
446
447       Note: here we use another means to escape the * operator by enclosing
448       the whole string in double quotes.
449
450       This graph looks much better. Speed is shown in km/h and there is even
451       an extra line with the maximum allowed speed (on the road I travel on).
452       I also changed the colors used to display speed and changed it from a
453       line into an area.
454
455       The calculations are more complex now. For speed measurements within
456       the speed limit they are:
457
458          Check if kmh is greater than 100    ( kmh,100 ) GT
459          If so, return 0, else kmh           ((( kmh,100 ) GT ), 0, kmh) IF
460
461       For values above the speed limit:
462
463          Check if kmh is greater than 100    ( kmh,100 ) GT
464          If so, return kmh, else return 0    ((( kmh,100) GT ), kmh, 0) IF
465
466   Graphics Magic
467       I like to believe there are virtually no limits to how RRDtool graph
468       can manipulate data. I will not explain how it works, but look at the
469       following PNG:
470
471          rrdtool graph speed4.png                           \
472             --start 920804400 --end 920808000               \
473             --vertical-label km/h                           \
474             DEF:myspeed=test.rrd:speed:AVERAGE              \
475             CDEF:nonans=myspeed,UN,0,myspeed,IF             \
476             CDEF:kmh=nonans,3600,*                          \
477             CDEF:fast=kmh,100,GT,100,0,IF                   \
478             CDEF:over=kmh,100,GT,kmh,100,-,0,IF             \
479             CDEF:good=kmh,100,GT,0,kmh,IF                   \
480             HRULE:100#0000FF:"Maximum allowed"              \
481             AREA:good#00FF00:"Good speed"                   \
482             AREA:fast#550000:"Too fast"                     \
483             STACK:over#FF0000:"Over speed"
484
485       Remember the note in the beginning?  I had to remove unknown data from
486       this example. The 'nonans' CDEF is new, and the 6th line (which used to
487       be the 5th line) used to read 'CDEF:kmh=myspeed,3600,*'
488
489       Let's create a quick and dirty HTML page to view the three PNGs:
490
491          <HTML><HEAD><TITLE>Speed</TITLE></HEAD><BODY>
492          <IMG src="speed2.png" alt="Speed in meters per second">
493          <BR>
494          <IMG src="speed3.png" alt="Speed in kilometers per hour">
495          <BR>
496          <IMG src="speed4.png" alt="Traveled too fast?">
497          </BODY></HTML>
498
499       Name the file "speed.html" or similar, and look at it in your web
500       browser.
501
502       Now, all you have to do is measure the values regularly and update the
503       database.  When you want to view the data, recreate the PNGs and make
504       sure to refresh them in your browser. (Note: just clicking reload may
505       not be enough, especially when proxies are involved.  Try shift-reload
506       or ctrl-F5).
507
508   Updates in Reality
509       We've already used the "update" command: it took one or more parameters
510       in the form of "<time>:<value>". You'll be glad to know that you can
511       specify the current time by filling in a "N" as the time.  Or you could
512       use the "time" function in Perl (the shortest example in this
513       tutorial):
514
515          perl -e 'print time, "\n" '
516
517       How to run a program on regular intervals is OS specific. But here is
518       an example in pseudo code:
519
520          - Get the value and put it in variable "$speed"
521          - rrdtool update speed.rrd N:$speed
522
523       (do not try this with our test database, we'll use it in further
524       examples)
525
526       This is all. Run the above script every five minutes. When you need to
527       know what the graphs look like, run the examples above. You could put
528       them in a script as well. After running that script, view the page
529       speed.html we created above.
530
531   Some words on SNMP
532       I can imagine very few people that will be able to get real data from
533       their car every five minutes. All other people will have to settle for
534       some other kind of counter. You could measure the number of pages
535       printed by a printer, for example, the cups of coffee made by the
536       coffee machine, a device that counts the electricity used, whatever.
537       Any incrementing counter can be monitored and graphed using the stuff
538       you learned so far. Later on we will also be able to monitor other
539       types of values like temperature.
540
541       Many people interested in RRDtool will use the counter that keeps track
542       of octets (bytes) transferred by a network device. So let's do just
543       that next. We will start with a description of how to collect data.
544
545       Some people will make a remark that there are tools which can do this
546       data collection for you. They are right! However, I feel it is
547       important that you understand they are not necessary. When you have to
548       determine why things went wrong you need to know how they work.
549
550       One tool used in the example has been talked about very briefly in the
551       beginning of this document, it is called SNMP. It is a way of talking
552       to networked equipment. The tool I use below is called "snmpget" and
553       this is how it works:
554
555          snmpget device password OID
556
557       or
558
559          snmpget -v[version] -c[password] device OID
560
561       For device you substitute the name, or the IP address, of your device.
562       For password you use the "community read string" as it is called in the
563       SNMP world.  For some devices the default of "public" might work,
564       however this can be disabled, altered or protected for privacy and
565       security reasons.  Read the documentation that comes with your device
566       or program.
567
568       Then there is this parameter, called OID, which means "object
569       identifier".
570
571       When you start to learn about SNMP it looks very confusing. It isn't
572       all that difficult when you look at the Management Information Base
573       ("MIB").  It is an upside-down tree that describes data, with a single
574       node as the root and from there a number of branches.  These branches
575       end up in another node, they branch out, etc.  All the branches have a
576       name and they form the path that we follow all the way down.  The
577       branches that we follow are named: iso, org, dod, internet, mgmt and
578       mib-2.  These names can also be written down as numbers and are 1 3 6 1
579       2 1.
580
581          iso.org.dod.internet.mgmt.mib-2 (1.3.6.1.2.1)
582
583       There is a lot of confusion about the leading dot that some programs
584       use.  There is *no* leading dot in an OID.  However, some programs can
585       use the above part of OIDs as a default.  To indicate the difference
586       between abbreviated OIDs and full OIDs they need a leading dot when you
587       specify the complete OID.  Often those programs will leave out the
588       default portion when returning the data to you.  To make things worse,
589       they have several default prefixes ...
590
591       Ok, lets continue to the start of our OID: we had 1.3.6.1.2.1 From
592       there, we are especially interested in the branch "interfaces" which
593       has number 2 (e.g., 1.3.6.1.2.1.2 or 1.3.6.1.2.1.interfaces).
594
595       First, we have to get some SNMP program. First look if there is a pre-
596       compiled package available for your OS. This is the preferred way.  If
597       not, you will have to get the sources yourself and compile those.  The
598       Internet is full of sources, programs etc. Find information using a
599       search engine or whatever you prefer.
600
601       Assume you got the program. First try to collect some data that is
602       available on most systems. Remember: there is a short name for the part
603       of the tree that interests us most in the world we live in!
604
605       I will give an example which can be used on Fedora Core 3.  If it
606       doesn't work for you, work your way through the manual of snmp and
607       adapt the example to make it work.
608
609          snmpget -v2c -c public myrouter system.sysDescr.0
610
611       The device should answer with a description of itself, perhaps an empty
612       one. Until you got a valid answer from a device, perhaps using a
613       different "password", or a different device, there is no point in
614       continuing.
615
616          snmpget -v2c -c public myrouter interfaces.ifNumber.0
617
618       Hopefully you get a number as a result, the number of interfaces.  If
619       so, you can carry on and try a different program called "snmpwalk".
620
621          snmpwalk -v2c -c public myrouter interfaces.ifTable.ifEntry.ifDescr
622
623       If it returns with a list of interfaces, you're almost there.  Here's
624       an example:
625          [user@host /home/alex]$ snmpwalk -v2c -c public cisco 2.2.1.2
626
627          interfaces.ifTable.ifEntry.ifDescr.1 = "BRI0: B-Channel 1"
628          interfaces.ifTable.ifEntry.ifDescr.2 = "BRI0: B-Channel 2"
629          interfaces.ifTable.ifEntry.ifDescr.3 = "BRI0" Hex: 42 52 49 30
630          interfaces.ifTable.ifEntry.ifDescr.4 = "Ethernet0"
631          interfaces.ifTable.ifEntry.ifDescr.5 = "Loopback0"
632
633       On this cisco equipment, I would like to monitor the "Ethernet0"
634       interface and from the above output I see that it is number four. I
635       try:
636
637          [user@host /home/alex]$ snmpget -v2c -c public cisco 2.2.1.10.4 2.2.1.16.4
638
639          interfaces.ifTable.ifEntry.ifInOctets.4 = 2290729126
640          interfaces.ifTable.ifEntry.ifOutOctets.4 = 1256486519
641
642       So now I have two OIDs to monitor and they are (in full, this time):
643
644          1.3.6.1.2.1.2.2.1.10
645
646       and
647
648          1.3.6.1.2.1.2.2.1.16
649
650       both with an interface number of 4.
651
652       Don't get fooled, this wasn't my first try. It took some time for me
653       too to understand what all these numbers mean. It does help a lot when
654       they get translated into descriptive text... At least, when people are
655       talking about MIBs and OIDs you know what it's all about.  Do not
656       forget the interface number (0 if it is not interface dependent) and
657       try snmpwalk if you don't get an answer from snmpget.
658
659       If you understand the above section and get numbers from your device,
660       continue on with this tutorial. If not, then go back and re-read this
661       part.
662
663   A Real World Example
664       Let the fun begin. First, create a new database. It contains data from
665       two counters, called input and output. The data is put into archives
666       that average it. They take 1, 6, 24 or 288 samples at a time.  They
667       also go into archives that keep the maximum numbers. This will be
668       explained later on. The time in-between samples is 300 seconds, a good
669       starting point, which is the same as five minutes.
670
671        1 sample "averaged" stays 1 period of 5 minutes
672        6 samples averaged become one average on 30 minutes
673        24 samples averaged become one average on 2 hours
674        288 samples averaged become one average on 1 day
675
676       Lets try to be compatible with MRTG which stores about the following
677       amount of data:
678
679        600 5-minute samples:    2   days and 2 hours
680        600 30-minute samples:  12.5 days
681        600 2-hour samples:     50   days
682        732 1-day samples:     732   days
683
684       These ranges are appended, so the total amount of data stored in the
685       database is approximately 797 days. RRDtool stores the data
686       differently, it doesn't start the "weekly" archive where the "daily"
687       archive stopped. For both archives the most recent data will be near
688       "now" and therefore we will need to keep more data than MRTG does!
689
690       We will need:
691
692        600 samples of 5 minutes  (2 days and 2 hours)
693        700 samples of 30 minutes (2 days and 2 hours, plus 12.5 days)
694        775 samples of 2 hours    (above + 50 days)
695        797 samples of 1 day      (above + 732 days, rounded up to 797)
696
697          rrdtool create myrouter.rrd         \
698                   DS:input:COUNTER:600:U:U   \
699                   DS:output:COUNTER:600:U:U  \
700                   RRA:AVERAGE:0.5:1:600      \
701                   RRA:AVERAGE:0.5:6:700      \
702                   RRA:AVERAGE:0.5:24:775     \
703                   RRA:AVERAGE:0.5:288:797    \
704                   RRA:MAX:0.5:1:600          \
705                   RRA:MAX:0.5:6:700          \
706                   RRA:MAX:0.5:24:775         \
707                   RRA:MAX:0.5:288:797
708
709       Next thing to do is to collect data and store it. Here is an example.
710       It is written partially in pseudo code,  you will have to find out what
711       to do exactly on your OS to make it work.
712
713          while not the end of the universe
714          do
715             get result of
716                snmpget router community 2.2.1.10.4
717             into variable $in
718             get result of
719                snmpget router community 2.2.1.16.4
720             into variable $out
721
722             rrdtool update myrouter.rrd N:$in:$out
723
724             wait for 5 minutes
725          done
726
727       Then, after collecting data for a day, try to create an image using:
728
729          rrdtool graph myrouter-day.png --start -86400 \
730                   DEF:inoctets=myrouter.rrd:input:AVERAGE \
731                   DEF:outoctets=myrouter.rrd:output:AVERAGE \
732                   AREA:inoctets#00FF00:"In traffic" \
733                   LINE1:outoctets#0000FF:"Out traffic"
734
735       This should produce a picture with one day worth of traffic.  One day
736       is 24 hours of 60 minutes of 60 seconds: 24*60*60=86400, we start at
737       now minus 86400 seconds. We define (with DEFs) inoctets and outoctets
738       as the average values from the database myrouter.rrd and draw an area
739       for the "in" traffic and a line for the "out" traffic.
740
741       View the image and keep logging data for a few more days.  If you like,
742       you could try the examples from the test database and see if you can
743       get various options and calculations to work.
744
745       Suggestion: Display in bytes per second and in bits per second. Make
746       the Ethernet graphics go red if they are over four megabits per second.
747
748   Consolidation Functions
749       A few paragraphs back I mentioned the possibility of keeping the
750       maximum values instead of the average values. Let's go into this a bit
751       more.
752
753       Recall all the stuff about the speed of the car. Suppose we drove at
754       144 km/h during 5 minutes and then were stopped by the police for 25
755       minutes.  At the end of the lecture we would take our laptop and create
756       and view the image taken from the database. If we look at the second
757       RRA we did create, we would have the average from 6 samples. The
758       samples measured would be 144+0+0+0+0+0=144, divided by 30 minutes,
759       corrected for the error by 1000, translated into km/h, with a result of
760       24 km/h.  I would still get a ticket but not for speeding anymore :)
761
762       Obviously, in this case we shouldn't look at the averages. In some
763       cases they are handy. If you want to know how many km you had traveled,
764       the averaged picture would be the right one to look at. On the other
765       hand, for the speed that we traveled at, the maximum numbers seen is
766       much more interesting. Later we will see more types.
767
768       It is the same for data. If you want to know the amount, look at the
769       averages. If you want to know the rate, look at the maximum.  Over
770       time, they will grow apart more and more. In the last database we have
771       created, there are two archives that keep data per day. The archive
772       that keeps averages will show low numbers, the archive that shows
773       maxima will have higher numbers.
774
775       For my car this would translate in averages per day of 96/24=4 km/h (as
776       I travel about 94 kilometers on a day) during working days, and maxima
777       of 120 km/h (my top speed that I reach every day).
778
779       Big difference. Do not look at the second graph to estimate the
780       distances that I travel and do not look at the first graph to estimate
781       my speed. This will work if the samples are close together, as they are
782       in five minutes, but not if you average.
783
784       On some days, I go for a long ride. If I go across Europe and travel
785       for 12 hours, the first graph will rise to about 60 km/h. The second
786       one will show 180 km/h. This means that I traveled a distance of 60
787       km/h times 24 h = 1440 km. I did this with a higher speed and a maximum
788       around 180 km/h. However, it probably doesn't mean that I traveled for
789       8 hours at a constant speed of 180 km/h!
790
791       This is a real example: go with the flow through Germany (fast!) and
792       stop a few times for gas and coffee. Drive slowly through Austria and
793       the Netherlands. Be careful in the mountains and villages. If you would
794       look at the graphs created from the five-minute averages you would get
795       a totally different picture. You would see the same values on the
796       average and maximum graphs (provided I measured every 300 seconds).
797       You would be able to see when I stopped, when I was in top gear, when I
798       drove over fast highways etc. The granularity of the data is much
799       higher, so you can see more. However, this takes 12 samples per hour,
800       or 288 values per day, so it would be a lot of data over a longer
801       period of time. Therefore we average it, eventually to one value per
802       day. From this one value, we cannot see much detail, of course.
803
804       Make sure you understand the last few paragraphs. There is no value in
805       only a line and a few axis, you need to know what they mean and
806       interpret the data in an appropriate way. This is true for all data.
807
808       The biggest mistake you can make is to use the collected data for
809       something that it is not suitable for. You would be better off if you
810       didn't have the graph at all.
811
812   Let's review what you now should know
813       You know how to create a database and can put data in it. You can get
814       the numbers out again by creating an image, do math on the data from
815       the database and view the result instead of the raw data.  You know
816       about the difference between averages and maximum, and when to use
817       which (or at least you should have an idea).
818
819       RRDtool can do more than what we have learned up to now. Before you
820       continue with the rest of this doc, I recommend that you reread from
821       the start and try some modifications on the examples. Make sure you
822       fully understand everything. It will be worth the effort and helps you
823       not only with the rest of this tutorial, but also in your day to day
824       monitoring long after you read this introduction.
825
826   Data Source Types
827       All right, you feel like continuing. Welcome back and get ready for an
828       increased speed in the examples and explanations.
829
830       You know that in order to view a counter over time, you have to take
831       two numbers and divide the difference of them by the time lapsed.  This
832       makes sense for the examples I gave you but there are other
833       possibilities.  For instance, I'm able to retrieve the temperature from
834       my router in three places namely the inlet, the so called hot-spot and
835       the exhaust.  These values are not counters.  If I take the difference
836       of the two samples and divide that by 300 seconds I would be asking for
837       the temperature change per second.  Hopefully this is zero! If not, the
838       computer room is probably on fire :)
839
840       So, what can we do?  We can tell RRDtool to store the values we measure
841       directly as they are (this is not entirely true but close enough). The
842       graphs we make will look much better, they will show a rather constant
843       value. I know when the router is busy (it works -> it uses more
844       electricity -> it generates more heat -> the temperature rises). I know
845       when the doors are left open (the room is air conditioned) -> the warm
846       air from the rest of the building flows into the computer room -> the
847       inlet temperature rises). Etc. The data type we use when creating the
848       database before was counter, we now have a different data type and thus
849       a different name for it. It is called GAUGE. There are more such data
850       types:
851
852        - COUNTER   we already know this one
853        - GAUGE     we just learned this one
854        - DERIVE
855        - ABSOLUTE
856
857       The two additional types are DERIVE and ABSOLUTE. Absolute can be used
858       like counter with one difference: RRDtool assumes the counter is reset
859       when it's read. That is: its delta is known without calculation by
860       RRDtool whereas RRDtool needs to calculate it for the counter type.
861       Example: our first example (12345, 12357, 12363, 12363) would read:
862       unknown, 12, 6, 0. The rest of the calculations stay the same.  The
863       other one, derive, is like counter. Unlike counter, it can also
864       decrease so it can have a negative delta. Again, the rest of the
865       calculations stay the same.
866
867       Let's try them all:
868
869          rrdtool create all.rrd --start 978300900 \
870                   DS:a:COUNTER:600:U:U \
871                   DS:b:GAUGE:600:U:U \
872                   DS:c:DERIVE:600:U:U \
873                   DS:d:ABSOLUTE:600:U:U \
874                   RRA:AVERAGE:0.5:1:10
875          rrdtool update all.rrd \
876                   978301200:300:1:600:300    \
877                   978301500:600:3:1200:600   \
878                   978301800:900:5:1800:900   \
879                   978302100:1200:3:2400:1200 \
880                   978302400:1500:1:2400:1500 \
881                   978302700:1800:2:1800:1800 \
882                   978303000:2100:4:0:2100    \
883                   978303300:2400:6:600:2400  \
884                   978303600:2700:4:600:2700  \
885                   978303900:3000:2:1200:3000
886          rrdtool graph all1.png -s 978300600 -e 978304200 -h 400 \
887                   DEF:linea=all.rrd:a:AVERAGE LINE3:linea#FF0000:"Line A" \
888                   DEF:lineb=all.rrd:b:AVERAGE LINE3:lineb#00FF00:"Line B" \
889                   DEF:linec=all.rrd:c:AVERAGE LINE3:linec#0000FF:"Line C" \
890                   DEF:lined=all.rrd:d:AVERAGE LINE3:lined#000000:"Line D"
891
892   RRDtool under the Microscope
893       • Line A is a COUNTER type, so it should continuously increment and
894         RRDtool must calculate the differences. Also, RRDtool needs to divide
895         the difference by the amount of time lapsed. This should end up as a
896         straight line at 1 (the deltas are 300, the time is 300).
897
898       • Line B is of type GAUGE. These are "real" values so they should match
899         what we put in: a sort of a wave.
900
901       • Line C is of type DERIVE. It should be a counter that can decrease.
902         It does so between 2400 and 0, with 1800 in-between.
903
904       • Line D is of type ABSOLUTE. This is like counter but it works on
905         values without calculating the difference. The numbers are the same
906         and as you can see (hopefully) this has a different result.
907
908       This translates in the following values, starting at 23:10 and ending
909       at 00:10 the next day (where "u" means unknown/unplotted):
910
911        - Line A:  u  u  1  1  1  1  1  1  1  1  1  u
912        - Line B:  u  1  3  5  3  1  2  4  6  4  2  u
913        - Line C:  u  u  2  2  2  0 -2 -6  2  0  2  u
914        - Line D:  u  1  2  3  4  5  6  7  8  9 10  u
915
916       If your PNG shows all this, you know you have entered the data
917       correctly, the RRDtool executable is working properly, your viewer
918       doesn't fool you, and you successfully entered the year 2000 :)
919
920       You could try the same example four times, each time with only one of
921       the lines.
922
923       Let's go over the data again:
924
925       • Line A: 300,600,900 and so on. The counter delta is a constant 300
926         and so is the time delta. A number divided by itself is always 1
927         (except when dividing by zero which is undefined/illegal).
928
929         Why is it that the first point is unknown? We do know what we put
930         into the database, right? True, But we didn't have a value to
931         calculate the delta from, so we don't know where we started. It would
932         be wrong to assume we started at zero so we don't!
933
934       • Line B: There is nothing to calculate. The numbers are as they are.
935
936       • Line C: Again, the start-out value is unknown. This is the same story
937         as for line A. In this case the deltas are not constant, therefore
938         the line is not either. If we would put the same numbers in the
939         database as we did for line A, we would have gotten the same line.
940         Unlike type counter, this type can decrease and I hope to show you
941         later on why this makes a difference.
942
943       • Line D: Here the device calculates the deltas. Therefore we DO know
944         the first delta and it is plotted. We had the same input as with line
945         A, but the meaning of this input is different and thus the line is
946         different.  In this case the deltas increase each time with 300. The
947         time delta stays at a constant 300 and therefore the division of the
948         two gives increasing values.
949
950   Counter Wraps
951       There are a few more basics to show. Some important options are still
952       to be covered and we haven't look at counter wraps yet. First the
953       counter wrap: In our car we notice that the counter shows 999987. We
954       travel 20 km and the counter should go to 1000007. Unfortunately, there
955       are only six digits on our counter so it really shows 000007. If we
956       would plot that on a type DERIVE, it would mean that the counter was
957       set back 999980 km. It wasn't, and there has to be some protection for
958       this. This protection is only available for type COUNTER which should
959       be used for this kind of counter anyways. How does it work? Type
960       counter should never decrease and therefore RRDtool must assume it
961       wrapped if it does decrease!  If the delta is negative, this can be
962       compensated for by adding the maximum value of the counter + 1. For our
963       car this would be:
964
965        Delta = 7 - 999987 = -999980    (instead of 1000007-999987=20)
966
967        Real delta = -999980 + 999999 + 1 = 20
968
969       At the time of writing this document, RRDtool knows of counters that
970       are either 32 bits or 64 bits of size. These counters can handle the
971       following different values:
972
973        - 32 bits: 0 ..           4294967295
974        - 64 bits: 0 .. 18446744073709551615
975
976       If these numbers look strange to you, you can view them in their
977       hexadecimal form:
978
979        - 32 bits: 0 ..         FFFFFFFF
980        - 64 bits: 0 .. FFFFFFFFFFFFFFFF
981
982       RRDtool handles both counters the same. If an overflow occurs and the
983       delta would be negative, RRDtool first adds the maximum of a small
984       counter + 1 to the delta. If the delta is still negative, it had to be
985       the large counter that wrapped. Add the maximum possible value of the
986       large counter + 1 and subtract the erroneously added small value.
987
988       There is a risk in this: suppose the large counter wrapped while adding
989       a huge delta, it could happen, theoretically, that adding the smaller
990       value would make the delta positive. In this unlikely case the results
991       would not be correct. The increase should be nearly as high as the
992       maximum counter value for that to happen, so chances are you would have
993       several other problems as well and this particular problem would not
994       even be worth thinking about. Even though, I did include an example, so
995       you can judge for yourself.
996
997       The next section gives you some numerical examples for counter-wraps.
998       Try to do the calculations yourself or just believe me if your
999       calculator can't handle the numbers :)
1000
1001       Correction numbers:
1002
1003        - 32 bits: (4294967295 + 1) =                                4294967296
1004        - 64 bits: (18446744073709551615 + 1)
1005                                           - correction1 = 18446744069414584320
1006
1007        Before:        4294967200
1008        Increase:                100
1009        Should become: 4294967300
1010        But really is:             4
1011        Delta:        -4294967196
1012        Correction1:  -4294967196 + 4294967296 = 100
1013
1014        Before:        18446744073709551000
1015        Increase:                             800
1016        Should become: 18446744073709551800
1017        But really is:                        184
1018        Delta:        -18446744073709550816
1019        Correction1:  -18446744073709550816
1020                                       + 4294967296 = -18446744069414583520
1021        Correction2:  -18446744069414583520
1022                          + 18446744069414584320 = 800
1023
1024        Before:        18446744073709551615 ( maximum value )
1025        Increase:      18446744069414584320 ( absurd increase, minimum for
1026        Should become: 36893488143124135935             this example to work )
1027        But really is: 18446744069414584319
1028        Delta:                     -4294967296
1029        Correction1:  -4294967296 + 4294967296 = 0
1030        (not negative -> no correction2)
1031
1032        Before:        18446744073709551615 ( maximum value )
1033        Increase:      18446744069414584319 ( one less increase )
1034        Should become: 36893488143124135934
1035        But really is: 18446744069414584318
1036        Delta:                     -4294967297
1037        Correction1:  -4294967297 + 4294967296 = -1
1038        Correction2:  -1 + 18446744069414584320 = 18446744069414584319
1039
1040       As you can see from the last two examples, you need strange numbers for
1041       RRDtool to fail (provided it's bug free of course), so this should not
1042       happen. However, SNMP or whatever method you choose to collect the
1043       data, might also report wrong numbers occasionally.  We can't prevent
1044       all errors, but there are some things we can do. The RRDtool "create"
1045       command takes two special parameters for this. They define the minimum
1046       and maximum allowed values. Until now, we used "U", meaning "unknown".
1047       If you provide values for one or both of them and if RRDtool receives
1048       data points that are outside these limits, it will ignore those values.
1049       For a thermometer in degrees Celsius, the absolute minimum is just
1050       under -273. For my router, I can assume this minimum is much higher so
1051       I would set it to 10, where as the maximum temperature I would set to
1052       80. Any higher and the device would be out of order.
1053
1054       For the speed of my car, I would never expect negative numbers and also
1055       I would not expect a speed  higher than 230. Anything else, and there
1056       must have been an error. Remember: the opposite is not true, if the
1057       numbers pass this check, it doesn't mean that they are correct. Always
1058       judge the graph with a healthy dose of suspicion if it seems weird to
1059       you.
1060
1061   Data Resampling
1062       One important feature of RRDtool has not been explained yet: it is
1063       virtually impossible to collect data and feed it into RRDtool on exact
1064       intervals. RRDtool therefore interpolates the data, so they are stored
1065       on exact intervals. If you do not know what this means or how it works,
1066       then here's the help you seek:
1067
1068       Suppose a counter increases by exactly one for every second. You want
1069       to measure it in 300 seconds intervals. You should retrieve values that
1070       are exactly 300 apart. However, due to various circumstances you are a
1071       few seconds late and the interval is 303. The delta will also be 303 in
1072       that case. Obviously, RRDtool should not put 303 in the database and
1073       make you believe that the counter increased by 303 in 300 seconds.
1074       This is where RRDtool interpolates: it alters the 303 value as if it
1075       would have been stored earlier and it will be 300 in 300 seconds.  Next
1076       time you are at exactly the right time. This means that the current
1077       interval is 297 seconds and also the counter increased by 297. Again,
1078       RRDtool interpolates and stores 300 as it should be.
1079
1080             in the RRD                 in reality
1081
1082        time+000:   0 delta="U"   time+000:    0 delta="U"
1083        time+300: 300 delta=300   time+300:  300 delta=300
1084        time+600: 600 delta=300   time+603:  603 delta=303
1085        time+900: 900 delta=300   time+900:  900 delta=297
1086
1087       Let's create two identical databases. I've chosen the time range
1088       920805000 to 920805900 as this goes very well with the example numbers.
1089
1090          rrdtool create seconds1.rrd   \
1091             --start 920804700          \
1092             DS:seconds:COUNTER:600:U:U \
1093             RRA:AVERAGE:0.5:1:24
1094
1095       Make a copy
1096
1097          for Unix: cp seconds1.rrd seconds2.rrd
1098          for Dos:  copy seconds1.rrd seconds2.rrd
1099          for vms:  how would I know :)
1100
1101       Put in some data
1102
1103          rrdtool update seconds1.rrd \
1104             920805000:000 920805300:300 920805600:600 920805900:900
1105          rrdtool update seconds2.rrd \
1106             920805000:000 920805300:300 920805603:603 920805900:900
1107
1108       Create output
1109
1110          rrdtool graph seconds1.png                       \
1111             --start 920804700 --end 920806200             \
1112             --height 200                                  \
1113             --upper-limit 1.05 --lower-limit 0.95 --rigid \
1114             DEF:seconds=seconds1.rrd:seconds:AVERAGE      \
1115             CDEF:unknown=seconds,UN                       \
1116             LINE2:seconds#0000FF                          \
1117             AREA:unknown#FF0000
1118          rrdtool graph seconds2.png                       \
1119             --start 920804700 --end 920806200             \
1120             --height 200                                  \
1121             --upper-limit 1.05 --lower-limit 0.95 --rigid \
1122             DEF:seconds=seconds2.rrd:seconds:AVERAGE      \
1123             CDEF:unknown=seconds,UN                       \
1124             LINE2:seconds#0000FF                          \
1125             AREA:unknown#FF0000
1126
1127       View both images together (add them to your index.html file) and
1128       compare. Both graphs should show the same, despite the input being
1129       different.
1130

WRAPUP

1132       It's time now to wrap up this tutorial. We covered all the basics for
1133       you to be able to work with RRDtool and to read the additional
1134       documentation available. There is plenty more to discover about RRDtool
1135       and you will find more and more uses for this package. You can easily
1136       create graphs using just the examples provided and using only RRDtool.
1137       You can also use one of the front ends to RRDtool that are available.
1138

MAILINGLIST

1140       Remember to subscribe to the RRDtool mailing list. Even if you are not
1141       answering to mails that come by, it helps both you and the rest of the
1142       users. A lot of the stuff that I know about MRTG (and therefore about
1143       RRDtool) I've learned while just reading the list without posting to
1144       it. I did not need to ask the basic questions as they are answered in
1145       the FAQ (read it!) and in various mails by other users. With thousands
1146       of users all over the world, there will always be people who ask
1147       questions that you can answer because you read this and other
1148       documentation and they didn't.
1149

SEE ALSO

1151       The RRDtool manpages
1152

AUTHOR

1154       I hope you enjoyed the examples and their descriptions. If you do, help
1155       other people by pointing them to this document when they are asking
1156       basic questions. They will not only get their answers, but at the same
1157       time learn a whole lot more.
1158
1159       Alex van den Bogaerdt <alex@vandenbogaerdt.nl>
1160
1161
1162
11631.8.0                             2022-03-14                    RRDTUTORIAL(1)
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