document explains the basics and may be boring. But if you don't
understand the basics, the examples will not be as meaningful to you.
-=head2 What is RRDtool ?
+=head2 What is RRDtool?
RRDtool refers to Round Robin Database tool.
Round robin is a technique that works with a fixed amount of data, and a
pointer to the current element. Think of a circle with some dots plotted
-on the edge, these dots are the places where data can be stored. Draw an
-arrow from the center of the circle to one of the dots, this is the pointer.
+on the edge -- these dots are the places where data can be stored. Draw an
+arrow from the center of the circle to one of the dots -- this is the pointer.
When the current data is read or written, the pointer moves to the next
-element. As we are on a circle there is no beginning nor an end, you can
-go on and on. After a while, all the available places will be used and
-the process automatically reuses old locations. This way, the database
+element. As we are on a circle there is neither a beginning nor an end, you can
+go on and on and on. After a while, all the available places will be used and
+the process automatically reuses old locations. This way, the dataset
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.
-=head2 What data can be put into an RRD ?
-
-You name it, it will probably fit. You should be able to measure some value
-at several points in time and provide this information to RRDtool. If you
-can do this, RRDtool will be able to store it. The values need to be
-numerical but don't have to be, as opposed to MRTG, integers.
-
-Many examples talk about SNMP which is an acronym for
-Simple Network Management Protocol. "Simple" refers to the protocol --
-it does not mean it is simple to manage or monitor a network. After working your
-way through this document, you should know enough to be able to understand
-what people are talking about. For now, just realize that SNMP is a way to
-ask devices for the values of counters they keep.
-It is the value from those counters that are kept in the RRD.
-
-=head2 What can I do with this tool ?
-
-RRDtool originated from MRTG (Multi Router Traffic Grapher). MRTG started
-as a tiny little script for graphing the use of a connection
-to the Internet. MRTG evolved into a tool for graphing other data sources
-including temperature, speed, voltage, number of printouts and
-the like. Most likely you will start to use the RRDtool to store
-and process data collected via SNMP. The data will most likely be bytes
-(or bits) transfered from and to a network or a computer.
-RRDtool lets you create a database, store data in it, retrieve that data
-and create graphs in PNG format for display on a web browser. Those PNG
-images are dependent on the data you collected and could be, for instance,
-an overview of the average network usage, or the peaks that occurred.
-It can also be used to display tidal waves, solar radiation, power
-consumption, number of visitors at an exhibition, noise levels near an
-airport, temperature on your favorite holiday location, temperature in the
-fridge and whatever you imagination can come up with. You need a sensor to
-measure the data and be able to feed the numbers to RRDtool.
-
-=head2 What if I still have problems after reading this document ?
+=head2 What data can be put into an RRD?
+
+XXX time series ??? XXX You name it, it will probably fit. You should
+be able to measure some value at several points in time and provide
+this information to RRDtool. If you can do this, RRDtool will be able
+to store it. The values must be numerical but don't have to be
+integers, as is the case with MRTG (the next section will give more
+details on this more specialized application).
+
+Many examples below 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
+understand what people are talking about. For now, just realize that
+SNMP can be used to query devices for the values of counters they keep. It
+is the value from those counters that we want to store in the RRD.
+
+=head2 What can I do with this tool?
+
+RRDtool originated from MRTG (Multi Router Traffic Grapher). MRTG
+started as a tiny little script for graphing the use of a university's
+connection to the Internet. MRTG was later (ab-)used as a tool for
+graphing other data sources including temperature, speed, voltage,
+number of printouts and the like.
+
+Most likely you will start to use RRDtool to store and process data
+collected via SNMP. The data will most likely be bytes (or bits)
+transfered from and to a network or a computer. But it can also be
+used to display tidal waves, solar radiation, power consumption,
+number of visitors at an exhibition, noise levels near an airport,
+temperature on your favorite holiday location, temperature in the
+fridge and whatever you imagination can come up with.
+
+You only need a sensor to measure the data and be able to feed the
+numbers into RRDtool. RRDtool then lets you create a database, store
+data in it, retrieve that data and create graphs in PNG format for
+display on a web browser. Those PNG 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.
+
+=head2 What if I still have problems after reading this document?
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 pre-compiled
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.
weeks and search the archive. It is considered rude to just ask
a question without searching the archives: your problem may already have been
solved for somebody else! This is true for most, if not all, mailing lists
-and not only for this particular list! Look in the documentation that
+and not only for this particular one. 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 E<lt>rrd-users-request@list.ee.ethz.chE<gt> with a
-subject of "subscribe". If you ever want to leave this list, you write
+subject of "subscribe". If you ever want to leave this list, just write
an email to the same address but now with a subject of "unsubscribe".
-=head2 How will you help me ?
+=head2 How will you help me?
By giving you some detailed descriptions with detailed examples.
-It is assumed that following the instructions in the order presented
+I assume that following the instructions in the order presented
will give you enough knowledge of RRDtool to experiment for yourself.
If it doesn't work the first time, don't give up. Reread the stuff that
you did understand, you may have missed something.
+
By following the examples you get some hands-on experience and, even
more important, some background information of how it works.
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
+increasing with every byte that is transfered. This counter will probably have
+a maximum value. If this value is reached and an extra byte is counted,
+the counter starts 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 !
+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
=item 2.
-Do the same with the current time and the previous time.
+Do the same with the current time and the previous time (in seconds).
=item 3.
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.
+For some people it may help to translate this to an 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).
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
+You are 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
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.
+minutes or 300 seconds. Our speed is 12000M / 300S or 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.
+We could also calculate the speed in KM/H: 12 times 5 minutes
+is an hour, so we have to multiply 12 KM by 12 to get 144 KM/H.
For our native English speaking friends: that's 90 MPH so don't
try this example at home or where I live :)
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
+OS to OS, but I assume you can figure it out if it works different on
+your's. Make sure you do not overwrite any file on your system when
executing the following command and type the whole line as one long
line (I had to split it for readability)
and skip all of the '\' characters.
(So enter: C<rrdtool create test.rrd --start 920804400 DS ...>)
-=head2 What has been created ?
+=head2 What has been created?
-We created the round robin database called test (test.rrd)
-which starts at noon the day I started (7th of march, 1999) writing
-this document. It holds one data source (DS) named "speed" that gets
-built from a counter. This counter is read every five minutes (default)
-In the same database two round robin archives (RRAs) are kept, one
-averages the data every time it is read (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 remaining options will be discussed later on.
+We created the round robin database called test (test.rrd) which
+starts at noon the day I started writing this document, 7th of March,
+1999 (this date translates to 920804400 seconds as explained
+below). Our database holds one data source (DS) named "speed" that
+represents 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).
+
+=for comment
+ XXX The remaining options will be discussed later on. (there aren't any
+ XXX in the example above, Fritz)
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.
+1st 1970 UTC. The time stamp value is translated into local time and
+it will therefore look different for 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
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.
+the real maximum per line is OS dependent.
We can now retrieve the data from our database using "rrdtool fetch":
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
+"NaN" in a different form. "NaN" stands for "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
to provide numbers like "0.04" in stead of "4.00000e-02". Those are
really the same numbers, just written down differently. Don't be
alarmed if a future version of rrdtool displays a slightly different
-form of output. The examples in this document are correct for version
-1.2.0
+form of output. The examples in this document are correct for version
+1.2.0 of RRDtool.
-What this output represents will become clear in the rest of the tutorial.
+The meaning of the above output will become clear below.
-=head2 It is time to create some graphics
+=head2 Time to create some graphics
Try the following command:
LINE2:myspeed#FF0000
This will create speed.png 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
+There is a definition of a variable called myspeed, using the data from RRA
+"speed" out of database "test.rrd". The line drawn is 2 pixels high
+and represents the variable myspeed. The color is red (specified by
+its rgb-representation, see below).
+
+You'll notice that the start of the graph is not at 12:00 but at 12:05.
+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.
When looking at the image, you notice that the horizontal axis is labeled
12:10, 12:20, 12:30, 12:40 and 12:50. Sometimes a label doesn't fit (12:00
and 13:00 would be candidates) so they are skipped.
-The vertical axis displays the range we entered. We provided kilometers
-and when divided by 300 seconds, we get very small numbers. To be exact,
-the first value was 12 (12357-12345) and divided by 300 this makes 0.04,
-which is displayed by RRDtool as "40 m" meaning "40/1000". The "m" has
-nothing to do with meters, kilometers or millimeters! RRDtool doesn't
-know about all this, it just works with numbers and not with meters...
-What we did wrong was that we should have measured in meters, this would
-have been (12357000-12345000)/300 = 12000/300 = 40.
+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" (milli) has nothing to do with meters,
+kilometers or millimeters! RRDtool doesn't know about the physical
+units of our data, it just works with dimensionless numbers.
-Let's correct that. We could recreate our database and store the correct
-data but there is a better way: do some calculations while creating the
-png file !
+If we had measured our distances in meters, this would have been
+(12357000-12345000)/300 = 12000/300 = 40.
+
+As most people have a better feel for numbers in this range, we'll
+correct that. We could recreate our database and store the correct
+data, but there is a better way: we do some calculations while creating
+the png file!
rrdtool graph speed2.png \
--start 920804400 --end 920808000 \
CDEF:realspeed=myspeed,1000,\* \
LINE2:realspeed#FF0000
-After viewing this PNG, 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 PNG should be the same.
+Note: Make sure not to forget the backslash \ in front of the
+multiplication operator * above. The backslash is needed to "escape"
+the * as some operating systems might interpret and expand * instead
+of passing it to the rrdtool command.
+
+After viewing this PNG, you notice the "m" (milli) 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 PNG should look the same.
-The calculations are in the CDEF part and are in Reverse Polish Notation
-("RPN"). What it says is: "take the data source myspeed and the number
-1000; multiply those". Don't bother with RPN yet, it will be explained
-later on in more detail. Also, you may want to read my tutorial on CDEFs
-and Steve Rader's tutorial on RPN. But first finish this tutorial.
+The calculations are specified in the CDEF part above and are in
+Reverse Polish Notation ("RPN"). What we requested RRDtool to do is:
+"take the data source myspeed and the number 1000; multiply
+those". Don't bother with RPN yet, it will be explained later on in
+more detail. Also, you may want to read my tutorial on CDEFs and Steve
+Rader's tutorial on RPN. But first finish this tutorial.
Hang on! If we can multiply values with 1000, it should also be possible
to display kilometers per hour from the same data!
+=for comment
+XXX strange format below: -*- ; Fritz
+
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
+ -*- Together this makes: value * (3600/1000) or 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:
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.
+Note: here we use another means to escape the * operator by enclosing
+the whole string in double quotes.
-The calculations are more complex now. For the "good" speed they are:
+This graph looks much better. Speed is shown in KM/H and there is even
+an extra line with the maximum allowed speed (on the road I travel
+on). 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 speed measurements within
+the speed limit 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:
+For values above the speed limit:
Check if kmh is greater than 100 ( kmh,100 ) GT
If so, return kmh, else return 0 ((( kmh,100) GT ), kmh, 0) IF
AREA:fast#550000:"Too fast" \
STACK:over#FF0000:"Over speed"
-Let's create a quick and dirty HTML page to view three PNGs:
+Let's create a quick and dirty HTML page to view the three PNGs:
<HTML><HEAD><TITLE>Speed</TITLE></HEAD><BODY>
<IMG src="speed2.png" alt="Speed in meters per second">
<IMG src="speed4.png" alt="Traveled too fast?">
</BODY></HTML>
-Name the file "speed.html" or similar, and view it.
+Name the file "speed.html" or similar, and look at it in your web browser.
Now, all you have to do is measure the values regularly and update the
database. When you want to view the data, recreate the PNGs and make
=head2 Updates in Reality
-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 :)
+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 specify the current time by filling in a "N" as the time.
+Or you could use the "time" function in Perl (the shortest example in
+this tutorial):
perl -e 'print time, "\n" '
-How you can run a program on regular intervals is OS specific. But here's
+How to run a program on regular intervals is OS specific. But here is
an example in pseudo code:
- Get the value, put it in variable "$speed"
- rrdtool update speed.rrd N:$speed
+ - Get the value and 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)
+(do not try this with our test database, we'll use it 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
+This is all. Run the above script every five minutes. When you need to know
+what the graphs look like, run the examples above. You could put them
+in a script as well. After running that script, view the page
+index.html we created above.
=head2 Some words on SNMP
-I can imagine very few people will be able to get real data from their
-car every five minutes, all other people will have to settle for some
-other kind of counter. You could measure the number of pages printed by
-a printer, the coffee made by the coffee machine, a device that counts
-the electricity used, whatever. Any incrementing counter can be monitored
-and graphed using the stuff you learned until now. Later on we will also
-be able to 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.
+I can imagine very few people that 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, for example, the cups of 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 so far. Later on we will also be able to monitor
+other types of values like temperature.
+
+Most (?) people interested in RRDtool will use the counter that keeps track
+of octets (bytes) transfered by a network device. So let's do just
+that next. We will start with a description of how to collect data.
+
Some people will make a remark that there are tools which 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
+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:
+beginning of this document, it is called SNMP. It is a way of talking
+to networked equipment. The tool I use below is called "snmpget" and
+this is how it works:
snmpget device password OID
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
+can use the 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
+Ok, 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.
+If not, you will have to get the sources yourself and compile those.
The Internet is full of sources, programs etc. Find information using
a search engine or whatever you prefer.
snmpget -v2c -c public myrouter 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.
+The device should answer with a description of itself, perhaps an
+empty one. 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 -v2c -c public myrouter interfaces.ifNumber.0
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:
+interface and from the above output I see that it is number four. I try:
[user@host /home/alex]$ snmpget -v2c -c public cisco 2.2.1.10.4 2.2.1.16.4
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
+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
+If you understand the above section and get numbers from your device, continue
on with this tutorial. If not, then go back and re-read this part.
=head2 A Real World Example
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:
+Lets try to be compatible with MRTG which 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!
+These ranges are appended, so the total amount of data stored in the
+database 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:
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
+Next thing to do is to collect data and store it. Here is an example.
+It is written partially in pseudo code, you will have to find out what
to do exactly on your OS to make it work.
while not the end of the universe
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:
+see if you can get various options and calculations to work.
-Display in bytes per second and in bits per second. Make the Ethernet
-graphics go red if they are over four megabits per second.
+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.
=head2 Consolidation Functions
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
+At the end of the lecture we would take our laptop and create and 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)
+Obviously, in this case we shouldn't look at the averages. In some
+cases they are handy. If you want to know how many KM you had traveled,
+the averaged picture would be the right one to look at. On the other hand, for
+the speed that we traveled at, the maximum numbers seen is much more
+interesting. 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.
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).
+(as I travel about 94 kilometers on a day) during working days, and
+maxima of 120 KM/H (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
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 !
+for 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. However, it probably 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
You would be able to see when I stopped, when I was in top gear, when
I drove over fast highways 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
+or 288 values per day, so it would be a lot of data over a longer
period of time. Therefore we average it, eventually to one value per
-day. From this one value, we cannot see much detail.
+day. From this one value, we cannot see much detail, of course.
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.
+interpret the data in ana appropriate 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 didn't have the graph at all.
-=head2 Let's review what you now should know.
+=head2 Let's review what you now should know
-You now know how to create a database. You can put the numbers in it,
-get them out again by creating an image, do math on the data from the
-database and view the outcome instead of the raw data.
-You know about the difference between averages and maxima, and when
-to use which (or at least you have an idea).
+You know how to create a database and can put data in it. You can get
+the numbers out again by creating an image, do math on the data from
+the database and view the resulte instead of the raw data. You know
+about the difference between averages and maxima, and when to use
+which (or at least you should 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
+you not only with the rest of this tutorial, but also in your day to day
monitoring long after you read this introduction.
=head2 Data Source Types
All right, you feel like continuing. Welcome back and get ready
-for an increased speed in the examples and explanation.
+for an increased speed in the examples and explanations.
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
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 :)
+Hopefully this is zero! If not, the computer room is probably on fire :)
-So, what can we do ? We can tell RRDtool to store the values we measure
+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
+air conditioned) -> 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:
- DERIVE
- ABSOLUTE
-The two new types are DERIVE and ABSOLUTE. Absolute can be used like
+The two additional 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.
=item *
-Line A is a counter so it should continuously increment and RRDtool
-should calculate the differences. Also, RRDtool needs to divide the
+Line A is a COUNTER type, so it should continuously increment and RRDtool
+must 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).
=item *
-Line C is derive. It should be a counter that can decrease. It does
+Line C is of type DERIVE. It should be a counter that can decrease. It does
so between 2400 and 0, with 1800 in-between.
=item *
-Line D is of type absolute. This is like counter but it works on
+Line D is of type ABSOLUTE. This is like counter but it works on
values without calculating the difference. The numbers are the same
and as you can see (hopefully) this has a different result.
=back
This translates in the following values, starting at 23:10 and ending
-at 00:10 the next day (where U means unknown/unplotted):
+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 PNG shows all this, you know you have typed the data correct,
-the RRDtool executable is working properly, your viewer doesn't fool you
+If your PNG shows all this, you know you have entered the data correctly,
+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.
=item *
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
+so is 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 !
+
+Why is it that the first point is unknown? We do know what we put into
+the database, right? 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!
=item *
-Line B: There is nothing to calculate. The numbers are as is.
+Line B: There is nothing to calculate. The numbers are as they are.
=item *
-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 C: Again, the start-out value is unknown. The same story is holds
+as for line A. In this case the deltas are not constant, therefore the line
+is not either. 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.
+this makes a difference.
=item *
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.
+first delta and it is plotted. We had the same input as with line A, but
+the meaning of this input is different and thus 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.
+increasing values.
=back
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,
+In our car we notice that the counter shows 999'987. We travel 20 KM and
+the counter should go to 1'000'007. Unfortunately, there are only six digits
+on our counter so it really shows 000'007. If we would plot that on a type
+DERIVE, it would mean that the counter was set back 999'980 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 !
+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)
+ Delta = 7 - 999'987 = -999'980 (instead of 1'000'007-999'987=20)
- Real delta = -999980 + 999999 + 1 = 20
+ Real delta = -999'980 + 999'999 + 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
+ - 32 bits: 0 .. 4'294'967'295
+ - 64 bits: 0 .. 18'446'744'073'709'551'615
-If these numbers look strange to you, you would like to view them in
+If these numbers look strange to you, you can view them in
their hexadecimal form:
- 32 bits: 0 .. FFFFFFFF
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.
+large counter + 1 and subtract the erroneously 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
+a huge delta, it could happen, theoretically, 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
+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.
+worth thinking about. Even though, I did include an example, so you
+can judge 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
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
+ - 32 bits: (4'294'967'295 + 1) = 4'294'967'296
+ - 64 bits: (18'446'744'073'709'551'615 + 1)
+ - correction1 = 18'446'744'069'414'584'320
+
+ Before: 4'294'967'200
+ Increase: 100
+ Should become: 4'294'967'300
+ But really is: 4
+ Delta: -4'294'967'196
+ Correction1: -4'294'967'196 + 4'294'967'296 = 100
+
+ Before: 18'446'744'073'709'551'000
+ Increase: 800
+ Should become: 18'446'744'073'709'551'800
+ But really is: 184
+ Delta: -18'446'744'073'709'550'816
+ Correction1: -18'446'744'073'709'550'816
+ + 4'294'967'296 = -18'446'744'069'414'583'520
+ Correction2: -18'446'744'069'414'583'520
+ + 18'446'744'069'414'584'320 = 800
+
+ Before: 18'446'744'073'709'551'615 ( maximum value )
+ Increase: 18'446'744'069'414'584'320 ( absurd increase, minimum for
+ Should become: 36'893'488'143'124'135'935 this example to work )
+ But really is: 18'446'744'069'414'584'319
+ Delta: -4'294'967'296
+ Correction1: -4'294'967'296 + 4'294'967'296 = 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
+ Before: 18'446'744'073'709'551'615 ( maximum value )
+ Increase: 18'446'744'069'414'584'319 ( one less increase )
+ Should become: 36'893'488'143'124'135'934
+ But really is: 18'446'744'069'414'584'318
+ Delta: -4'294'967'297
+ Correction1: -4'294'967'297 + 4'294'967'296 = -1
+ Correction2: -1 + 18'446'744'069'414'584'320 = 18'446'744'069'414'584'319
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
+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
+the minimum and maximum allowed values. 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
+receives data points 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.
+so I would set it to 10, where as the maximum temperature I would
+set to 80. Any higher and the device would be out of order.
+
+For the speed of my car, I would never expect negative numbers and
+also I would not expect a speed 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 suspicion if it
+seems weird to you.
=head2 Data Resampling
-One important feature of RRDtool has not been explained yet:
-It is virtually impossible to collect the data and feed it into RRDtool
-on exact intervals. RRDtool therefore interpolates the data so it is on
-exact intervals. If you do not know what this means or how it works,
-then here's the help you seek:
+One important feature of RRDtool has not been explained yet: it is
+virtually impossible to collect data and feed it into RRDtool on exact
+intervals. RRDtool therefore interpolates the data, so they are stored
+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
+Suppose a counter increases by 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.
+303 in that case. Obviously, RRDtool should not put 303 in the database
+and make you believe that the counter increased by 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.
+interval is 297 seconds and also the counter increased by 297. Again,
+RRDtool interpolates and stores 300 as it should be.
in the RRD in reality
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.
+Let's create two identical databases. I've chosen the time range 920'805'000
+to 920'805'900 as this goes very well with the example numbers.
rrdtool create seconds1.rrd \
--start 920804700 \
AREA:unknown#FF0000
View both images together (add them to your index.html file)
-and compare. Both graphs should show the same, despite the
+and compare. Both graphs should show the same, despite the
input being different.
=head1 WRAPUP
-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.
+It's time now to wrap up this tutorial. We covered all the basics for
+you to be able to work with RRDtool and to read the additional
+documentation available. There is plenty more to discover about
+RRDtool and you will find more and more uses for this package. You can
+easly create graphs using just the examples provided and using only
+RRDtool. You can also use one of the front ends to RRDtool that are
+available.
=head1 MAILINGLIST
-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
+Remember to subscribe to the RRDtool mailing list. Even if you are not
+answering to mails that come by, it helps both you and the rest of the
+users. 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.
=head1 SEE ALSO
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
+basic questions. They will not only get their answers, but at the same
time learn a whole lot more.
Alex van den Bogaerdt
projects / rrdtool.git / commitdiff