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
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).
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 examples)
This is all. Run this script every five minutes. When you need to know what the graphics look like, run the examples above. You could put them in a script. After running that script, view index.html
I can imagine very few people will be able to get real data from their car every five minutes, all other people will have to settle for some other kind of counter. You could measure the number of pages printed by a printer, the coffee made by the coffee machine, a device that counts the electricity used, whatever. Any incrementing counter can be monitored and graphed using the stuff you learned until now. Later on we will also be able to monitor other types of values like temperature. Most people will use the counter that keeps track of octets (bytes) transfered by a network device so we have to do just that. We will start with a description of how to collect data. Some people will make a remark that there are tools who can do this data collection for you. They are right! However, I feel it is important that you understand they are not necessary. When you have to determine why things went wrong you need to know how they work.
One tool used in the example has been talked about very briefly in the beginning of this document, it is called SNMP. It is a way of talking to equipment. The tool I use below is called ``snmpget'' and this is how it works:
snmpget device password OID
For device you substitute the name, or the IP address, of your device. For password you use the ``community read string'' as it is called in the SNMP world. For some devices the default of ``public'' might work, however this can be disabled, altered or protected for privacy and security reasons. Read the documentation that comes with your device or program.
Then there is this third parameter, called OID, which means ``object identifier''.
When you start to learn about SNMP it looks very confusing. It isn't all that difficult when you look at the Management Information Base (``MIB''). It is an upside-down tree that describes data, with a single node as the root and from there a number of branches. These branches end up in another node, they branch out, etc. All the branches have a name and they form the path that we follow all the way down. The branches that we follow are named: iso, org, dod, internet, mgmt and mib-2. These names can also be written down as numbers and are 1 3 6 1 2 1.
iso.org.dod.internet.mgmt.mib-2 (1.3.6.1.2.1)
There is a lot of confusion about the leading dot that some programs use. There is *no* leading dot in an OID. However, some programs can use above part of OIDs as a default. To indicate the difference between abbreviated OIDs and full OIDs they need a leading dot when you specify the complete OID. Often those programs will leave out the default portion when returning the data to you. To make things worse, they have several default prefixes ...
Right, lets continue to the start of our OID: we had 1.3.6.1.2.1 From there, we are especially interested in the branch ``interfaces'' which has number 2 (eg 1.3.6.1.2.1.2 or 1.3.6.1.2.1.interfaces).
First, we have to get some SNMP program. First look if there is a pre-compiled package available for your OS. This is the preferred way. If not, you will have to get yourself the sources and compile those. The Internet is full of sources, programs etc. Find information using a search engine or whatever you prefer. As a suggestion: look for CMU-SNMP. It is commonly used.
Assume you got the program. First try to collect some data that is available on most systems. Remember: there is a short name for the part of the tree that interests us most in the world we live in!
I will use the short version as I think this document is large enough as it is. If that doesn't work for you, prefix with .1.3.6.1.2.1 and try again. Also, Read The Fine Manual. Skip the parts you cannot understand yet, you should be able to find out how to start the program and use it.
snmpget myrouter public system.sysdescr.0
The device should answer with a description of itself, perhaps empty. Until you got a valid answer from a device, perhaps using a different ``password'', or a different device, there is no point in continuing.
snmpget myrouter public interfaces.ifnumber.0
Hopefully you get a number as a result, the number of interfaces. If so, you can carry on and try a different program called ``snmpwalk''.
snmpwalk myrouter public interfaces.iftable.ifentry.ifdescr
If it returns with a list of interfaces, you're almost there. Here's an example: [user@host /home/alex]$ snmpwalk cisco public 2.2.1.2
interfaces.ifTable.ifEntry.ifDescr.1 = "BRI0: B-Channel 1" interfaces.ifTable.ifEntry.ifDescr.2 = "BRI0: B-Channel 2" interfaces.ifTable.ifEntry.ifDescr.3 = "BRI0" Hex: 42 52 49 30 interfaces.ifTable.ifEntry.ifDescr.4 = "Ethernet0" interfaces.ifTable.ifEntry.ifDescr.5 = "Loopback0"
On this cisco equipment, I would like to monitor the ``Ethernet0'' interface and see that it is number four. I try:
[user@host /home/alex]$ snmpget cisco public 2.2.1.10.4 2.2.1.16.4
interfaces.ifTable.ifEntry.ifInOctets.4 = 2290729126 interfaces.ifTable.ifEntry.ifOutOctets.4 = 1256486519
So now I have two OIDs to monitor and they are (in full, this time):
1.3.6.1.2.1.2.2.1.10
and
1.3.6.1.2.1.2.2.1.16
both with an interface number of 4.
Don't get fooled, this wasn't my first try. It took some time for me too to understand what all these numbers mean, it does help a lot when they get translated into descriptive text... At least, when people are talking about MIBs and OIDs you know what it's all about. Do not forget the interface number (0 if it is not interface dependent) and try snmpwalk if you don't get an answer from snmpget.
If you understand above part, and get numbers from your device, continue on with this tutorial. If not, then go back and re-read this part.
Let the fun begin. First, create a new database. It contains data from two counters, called input and output. The data is put into archives that average it. They take 1, 6, 24 or 288 samples at a time. They also go into archives that keep the maximum numbers. This will be explained later on. The time in-between samples is 300 seconds, a good starting point, which is the same as five minutes.
1 sample "averaged" stays 1 period of 5 minutes 6 samples averaged become one average on 30 minutes 24 samples averaged become one average on 2 hours 288 samples averaged become one average on 1 day
Lets try to be compatible with MRTG: MRTG stores about the following amount of data:
600 5-minute samples: 2 days and 2 hours 600 30-minute samples: 12.5 days 600 2-hour samples: 50 days 732 1-day samples: 732 days
These ranges are appended so the total amount of data kept is approximately 797 days. RRDtool stores the data differently, it doesn't start the ``weekly'' archive where the ``daily'' archive stopped. For both archives the most recent data will be near ``now'' and therefore we will need to keep more data than MRTG does!
We will need:
600 samples of 5 minutes (2 days and 2 hours) 700 samples of 30 minutes (2 days and 2 hours, plus 12.5 days) 775 samples of 2 hours (above + 50 days) 797 samples of 1 day (above + 732 days, rounded up to 797)
rrdtool create myrouter.rrd \
DS:input:COUNTER:600:U:U \
DS:output:COUNTER:600:U:U \
RRA:AVERAGE:0.5:1:600 \
RRA:AVERAGE:0.5:6:700 \
RRA:AVERAGE:0.5:24:775 \
RRA:AVERAGE:0.5:288:797 \
RRA:MAX:0.5:1:600 \
RRA:MAX:0.5:6:700 \
RRA:MAX:0.5:24:775 \
RRA:MAX:0.5:288:797
Next thing to do is collect data and store it. Here is an example. It is written partially in pseudo code so you will have to find out what to do exactly on your OS to make it 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.
A few paragraphs back I mentioned the possibility of keeping the maximum values instead of the average values. Let's go into this a bit more.
Recall all the stuff about the speed of the car. Suppose we drove at 144 KM/H during 5 minutes and then were stopped by the police for 25 minutes. At the end of the lecture we would take our laptop and create+view the image taken from the database. If we look at the second RRA we did create, we would have the average from 6 samples. The samples measured would be 144+0+0+0+0+0=144, divided by 30 minutes, corrected for the error by 1000, translated into KM/H, with a result of 24 KM/H. I would still get a ticket but not for speeding anymore :)
Obviously, in this case, we shouldn't look at the averages. In some cases they are handy. If you want to know how much KM you had traveled, the picture would be the right one to look at. On the other hand, for the speed that we traveled at, the maximum number seen is much more valuable. (later we will see more types)
It is the same for data. If you want to know the amount, look at the averages. If you want to know the rate, look at the maximum. Over time, they will grow apart more and more. In the last database we have created, there are two archives that keep data per day. The archive that keeps averages will show low numbers, the archive that shows maxima will have higher numbers. For my car this would translate in averages per day of 96/24=4 KM/H (as I travel about 94 kilometers on a day) during week days, and maximum of 120 KM/H on weekdays (my top speed that I reach every day).
Big difference. Do not look at the second graph to estimate the distances that I travel and do not look at the first graph to estimate my speed. This will work if the samples are close together, as they are in five minutes, but not if you average.
On some days, I go for a long ride. If I go across Europe and travel for over 12 hours, the first graph will rise to about 60 KM/H. The second one will show 180 KM/H. This means that I traveled a distance of 60 KM/H times 24 H = 1440 KM. I did this with a higher speed and a maximum around 180 KM/H. This doesn't mean that I traveled for 8 hours at a constant speed of 180 KM/H ! This is a real example: go with the flow through Germany (fast!) and stop a few times for gas and coffee. Drive slowly through Austria and the Netherlands. Be careful in the mountains and villages. If you would look at the graphs created from the five-minute averages you would get a totally different picture. You would see the same values on the average and maximum graphs (provided I measured every 300 seconds). You would be able to see when I stopped, when I was in top gear, when I drove over fast hiways etc. The granularity of the data is much higher, so you can see more. However, this takes 12 samples per hour, or 288 values per day, so it would be too much to keep for a long period of time. Therefore we average it, eventually to one value per day. From this one value, we cannot see much detail.
Make sure you understand the last few paragraphs. There is no value in only a line and a few axis, you need to know what they mean and interpret the data in a good way. This is true for all data.
The biggest mistake you can make is to use the collected data for something that it is not suitable for. You would be better off if you would not have the graphics at all in that case.
You now know how to create a database. You can put the numbers in it, get them out again by creating an image, do math on the data from the database and view the outcome instead of the raw data. You know about the difference between averages and maxima, and when to use which (or at least you have an idea).
RRDtool can do more than what we have learned up to now. Before you continue with the rest of this doc, I recommend that you reread from the start and try some modifications on the examples. Make sure you fully understand everything. It will be worth the effort and helps you not only with the rest of this doc but also in your day to day monitoring long after you read this introduction.
All right, you feel like continuing. Welcome back and get ready for an increased speed in the examples and explanation.
You know that in order to view a counter over time, you have to take two numbers and divide the difference of them between the time lapsed. This makes sense for the examples I gave you but there are other possibilities. For instance, I'm able to retrieve the temperature from my router in three places namely the inlet, the so called hot-spot and the exhaust. These values are not counters. If I take the difference of the two samples and divide that by 300 seconds I would be asking for the temperature change per second. Hopefully this is zero! If not, the computerroom is on fire :)
So, what can we do ? We can tell RRDtool to store the values we measure directly as they are (this is not entirely true but close enough). The graphs we make will look much better, they will show a rather constant value. I know when the router is busy (it works -> it uses more electricity -> it generates more heat -> the temperature rises). I know when the doors are left open (the room is cooled -> the warm air from the rest of the building flows into the computer room -> the inlet temperature rises) etc. The data type we use when creating the database before was counter, we now have a different data type and thus a different name for it. It is called GAUGE. There are more such data types:
- COUNTER we already know this one - GAUGE we just learned this one - DERIVE - ABSOLUTE
The two new types are DERIVE and ABSOLUTE. Absolute can be used like counter with one difference: RRDtool assumes the counter is reset when it's read. That is: its delta is known without calculation by RRDtool whereas RRDtool needs to calculate it for the counter type. Example: our first example (12345, 12357, 12363, 12363) would read: unknown, 12, 6, 0. The rest of the calculations stay the same. The other one, derive, is like counter. Unlike counter, it can also decrease so it can have a negative delta. Again, the rest of the calculations stay the same.
Let's try them all:
rrdtool create all.rrd --start 978300900 \
DS:a:COUNTER:600:U:U \
DS:b:GAUGE:600:U:U \
DS:c:DERIVE:600:U:U \
DS:d:ABSOLUTE:600:U:U \
RRA:AVERAGE:0.5:1:10
rrdtool update all.rrd \
978301200:300:1:600:300 \
978301500:600:3:1200:600 \
978301800:900:5:1800:900 \
978302100:1200:3:2400:1200 \
978302400:1500:1:2400:1500 \
978302700:1800:2:1800:1800 \
978303000:2100:4:0:2100 \
978303300:2400:6:600:2400 \
978303600:2700:4:600:2700 \
978303900:3000:2:1200:3000
rrdtool graph all1.gif -s 978300600 -e 978304200 -h 400 \
DEF:linea=all.rrd:a:AVERAGE LINE3:linea#FF0000:"Line A" \
DEF:lineb=all.rrd:b:AVERAGE LINE3:lineb#00FF00:"Line B" \
DEF:linec=all.rrd:c:AVERAGE LINE3:linec#0000FF:"Line C" \
DEF:lined=all.rrd:d:AVERAGE LINE3:lined#000000:"Line D"
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:
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 calculator can't handle the numbers :)
Correction numbers:
- 32 bits: (4294967295+1) = 4294967296 - 64 bits: (18446744073709551615+1)-correction1 = 18446744069414584320
Before: 4294967200 Increase: 100 Should become: 4294967300 But really is: 4 Delta: -4294967196 Correction1: -4294967196 +4294967296 = 100
Before: 18446744073709551000 Increase: 800 Should become: 18446744073709551800 But really is: 184 Delta: -18446744073709550816 Correction1: -18446744073709550816 +4294967296 = -18446744069414583520 Correction2: -18446744069414583520 +18446744069414584320 = 800
Before: 18446744073709551615 ( maximum value ) Increase: 18446744069414584320 ( absurd increase, minimum for Should become: 36893488143124135935 this example to work ) But really is: 18446744069414584319 Delta: -4294967296 Correction1: -4294967296 + 4294967296 = 0 (not negative -> no correction2)
Before: 18446744073709551615 ( maximum value ) Increase: 18446744069414584319 ( one less increase ) Should become: 36893488143124135934 But really is: 18446744069414584318 Delta: -4294967297 Correction1: -4294967297 +4294967296 = -1 Correction2: -1 +18446744069414584320 = 18446744069414584319
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.
One important feature of RRDtool has not been explained yet: It is virtually impossible to collect the data and feed it into RRDtool on exact intervals. RRDtool therefore interpolates the data so it is on exact intervals. If you do not know what this means or how it works, then here's the help you seek:
Suppose a counter increases with exactly one for every second. You want to measure it in 300 seconds intervals. You should retrieve values that are exactly 300 apart. However, due to various circumstances you are a few seconds late and the interval is 303. The delta will also be 303 in that case. Obviously RRDtool should not put 303 in the database and make you believe that the counter increased 303 in 300 seconds. This is where RRDtool interpolates: it alters the 303 value as if it would have been stored earlier and it will be 300 in 300 seconds. Next time you are at exactly the right time. This means that the current interval is 297 seconds and also the counter increased with 297. Again RRDtool alters the value and stores 300 as it should be.
in the RDD in reality
time+000: 0 delta="U" time+000: 0 delta="U" time+300: 300 delta=300 time+300: 300 delta=300 time+600: 600 delta=300 time+603: 603 delta=303 time+900: 900 delta=300 time+900: 900 delta=297
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.
It's time to wrap up this document. You now know all the basics to be able to work with RRDtool and to read the documentation available. There is plenty more to discover about RRDtool and you will find more and more uses for the package. You could create easy graphics using just the examples provided and using only RRDtool. You could also use the front ends that are available.
Remember to subscribe to the mailing-list. Even if you are not answering the mails that come by, it helps both you and the rest. A lot of the stuff that I know about MRTG (and therefore about RRDtool) I've learned while just reading the list without posting to it. I did not need to ask the basic questions as they are answered in the FAQ (read it!) and in various mails by other users. With thousands of users all over the world, there will always be people who ask questions that you can answer because you read this and other documentation and they didn't.
The RRDtool manpages
I hope you enjoyed the examples and their descriptions. If you do, help other people by pointing them to this 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>