Gnuplot, dstat - easy graphing on Linux

Recently, started fiddling around with how to monitor and graph performance data on linux boxes. Other than the usual tools like top and vmstat, which are either interactive (top) or too textual to do anything much.

First off, vmstat, doesnt lend itself well to graphing without additional scripts to lay out the data so tools like gnuplot can be used. Secondly, and more seriously, it doesn’t include a timestamp in the output.

Looking around a bit found that dstat seems to be a good replacement to vmstat (and iostat) - and the generated data is consumable with gnuplot.

Here’s a quick example of generating graphs for CPU user, system and idle times

dstat -tc 5 500 > dstat.raw

now fire up gnuplot and go ahead and plot it

gnuplot> set xdata time gnuplot> set timefmt "%s" gnuplot> set format x "%M:%S" gnuplot> plot "dstat.raw" using 1:2 title "User" with lines, "dstat.raw" using 1:3 title "Sys" with lines, "dstat.raw" using 1:4 title "Idle" using lines

To make gnuplot generat an output file, you need

gnuplot> set term png

gnuplot> set output “dstat.png”

gnuplot> replot

And you’re done. here’s the graph generated on my machine. There’s loads more that you can do - and admittedly, you can do everything by dumping your file to excel. However, that doesn’t lend itself well to a completely automated process. When you’re doing performance testing and such like, you will likely repeat this enough number of times. Not having to do it manually helps big time!

Working with huge XML files - tools of the trade.

XMLStarlet is great for slicing and dicing huge XML files. Had a run in recently - had a 80 Mb XML file in a single line :D. Guess what, most editors that I tried balked and fell over. This was on a 2Gig Core2 Duo machine.

XMLSpy, vi, emacs, notepad++ all died - and trying to do something with a 80 Gig XML where the 80 gigs are on a single line isnt much fun. So the first order of business was to pretty print the XML. XMLstarlet worked great -

xmlstarlet fo file.xml > output.xml

and you’re done.

The next order of business was that we needed to validate the XML document against a schema. Our first attempt was with Sun’s multi schema validator (MSV). MSV does not validate the whole document but instead stops after a certain number of failures. So, MSV - out, XMLStarlet in. XMLStarlet can validate documents again W3C schema, DTD  or a RELAXNG schema.

xmlstarlet val --err --xsd schema.xsd input.xml >  errors.txt

And presto! - you get an error report that you can slice and dice with sed/awk or anything else at all.

XMLStarlet also allows you to write Xpaths to query the xml - however, I found the syntax too weird and round about. A better alternative is a perl based solutions - XSH2 - a command line xml editing shell. You can install it under cygwin and it supports basic command pipelining and redirection.

So go ahead and launch XSH. At your cygwin prompt

[~]xsh
—————————————
 xsh - XML Editing Shell version 2.1.1
—————————————

Copyright (c) 2002 Petr Pajas.
This is free software, you may use it and distribute it under
either the GNU GPL Version 2, or under the Perl Artistic License.
Using terminal type: Term::ReadLine::Gnu
Hint: Type `help’ or `help | less’ to get more help.
$scratch/>

Now, lets load up our document, type

$scratch/>$x:=open formatted.xml

Your prompt changes to

$x/>

So go ahead and try a few xpaths

$x/> ls /path/to/node

and XSH prints out the matching nodes. Now what if you need to create a document fragment of nodes matching a certain xpath? Piece of cake - do ahead

$x/> ls /path/to/node | tee fragment.xml

XSH2 has many, many more features - but this should be good enough to get you off the ground.

HOWTO: Access your machine from the internet without a static IP

For machines to be accessible on the internet, usually you need a static IP that’s leased from your ISP so that when someone types in your IP address, so that packets can be routed over to your machine. However, getting a static ip is costly and for the most part, internet users have dynamic IP address that the ISP allocates each time an end user connects to the internet. Since the ip address keeps changing on each connection, there’s no straightforward way to connect to the machine without knowing the IP address that’s been allocated - or so it was at least till Dynamic DNS came along (it isnt new - has been around for ages, but for some reason isn’t that well known)

Typically, when you type in www.google.com in your browser, your machine performs a DNS (Domain name service) lookup with the DNS servers from your ISP to find out the IP address corresponding to www.google.com. With DDNS (dynamic DNS) this is made to work with your dynamically allocated IP address also. Here’s how it works

1. Register with a DDNS service provider. Service provider provide free accounts for personal use - go to www.dyndns.org
2. Once you’ve created your account, go ahead and set up your hostname. DDNS service providers will have some domains that you can choose from and you get to choose the host part. For a fee, you can also use a domain name of your choice.
3. If your set up has a router at your end, check your router administration page if it supports dynamic DNS. If it does, you need to enter the hostname, account and password. Everytime your router connects to the internet, it sends an update notification to the DDNS service notifying the new IP obtained from your ISP. The DDNS service takes care of sending update notifications to routers on the internet.
4. If you dont have a router, then download the DDNS client software from the service provider. Most DDNS providers have windows, mac and linux clients. These run on your machine and do the same thing - notify the DDNS service provider of your new IP whenever you establish a connection with your ISP.
5. If you’ve got all this set up, then you can reach your machine from the net - try ping <your host name>

If you’re running Linux/Ubuntu, make sure your’re running SSH service and try ssh <your host name>. If you have a router setup, then you will need an additional step - basically the DDNS name refers to your router IP - and not the machine behind the router that you wish to reach. You will also need to make sure that your machine has a static IP from your router. To set up your router, go to your router administration page.

1. Go to the LAN section and give a range of IPs outside of the static IP. Most routers have lan addresses like 192.168.x.y - 192.168.x.z. If you want your host to have an IP address of 192.168.1.100, then give a LAN range that does not include this IP - say 192.168.1.110 - 192.168.1.200.
2. Save and reboot your router.
3. Now go to your network settings and enter your static IP (192.168.1.100), netmask 255.255.255.255, gateway (usually 192.168.1.1).
4. Go to your router administration page and look for a section like virtual server - your router will allow you to forward packets received on a particular port to a host and port within your LAN. You will have to enter the external port (we’ll use 22), the internal machine to forward (192.168.1.100) and the port to forward to (22). With this in place, any packets received on port 22 (ssh) on your router will be forwarded to the 192.168.1.100 machine on the ssh port.
5. Save and reboot your router.
6. Give it a spin.

From a different machine (or from the same one -doesnt matter), try out ssh <your host> and you should be able to login to your machine - via the internet.