Category: Tech Tips

If you run into a problem where your dnsmasq DNS server is not responding to dns queries from separate subnets than the DNS server’s subnet, try setting the listen-address to the DNS server’s IP (e.g. where you’re running dnsmasq).

On the Ubiquiti EdgeRouter Lite (which is based on mips Debian wheezy) the file to change is:

(make it if it doesn’t exist)

add this to that file:

Where <DNS-SERVER-IP> is the IP of your machine that’s running dnsmasq.

If you’re running dnsmasq from the command line, without using the conf files, add this parameter

Starting with two laptops connected to one ERL each. ERLs both running 1.5.0.

Laptop A <-> ERL <-> ERL <-> Laptop B
192.168.20.100 <-> 192.168.20.1 192.168.1.2 <-> 192.168.1.1 192.168.10.1 <-> 192.168.10.100

 

I’m using OSPF to expose these two networks to each other for this test. See EdgeRouter Lite Simple OSPF Guide

iperf results from one laptop to the other:

 Near wire. Great!

 Next we’ll remove the OSPF routing and setup an IPSec tunnel between the two an retest.

I used the GUI’s IPSec site-to-site feature to set this up. Here’s what it generated:

And the results with IPSec hardware offload disabled.

And with IPSec hardware offload enabled.

Not bad!

However, even with IPSec enabled, load average increases a good bit when pushing max data through the IPSec VPN

Compared to without pushing data

While this didn’t seem to affect the usage of the router, it is a little worrying. I don’t have any firewalls or other services enabled on the router. What happens when we take this into the real world? It’s worth noting that this is a dual core router, so really that’s only 1/4 of total processing power.

Here’s a really simple OSPF setup on two Ubiquiti Edge Router Lites.

Two ERLs hooked together via eth0.

ERL20 <-> ERL10
192.168.20.1 192.168.1.2 <-> 192.168.1.1 192.168.10.1

on ERL20 get into configure and run the following:

on ERL10 get into configure and run the following.

run ‘commit’ on both them, (‘save’ if you want to) and ‘exit’ to prompt.

Now watch ospf work it’s magic.

Now you should have routes

 

Removing the Base Cover on the Dell Vostro 3560 is quite tricky.

Here’s what the manual says to do:

 

Seems easy enough. In actuality it’s much harder. The cover won’t slide. You have to work your way around the edges with a small screw driver. Be very careful since the base cover is plastic.

Your goal is to get each one of these plastic lips out.

 

There are 13 of them as seen below.

Another view of these annoying little bastards.

 

Here’s what the 3560 looks like with the base cover removed.

 

Good luck!

 

I often type random notes into a Notepad++ new file (AKA untitled). Sometimes these are important notes that I don’t want to loose. Most of the time I remember to save these somewhere, or at least I remember when closing Notepad++. But on one occasion I forgot the save it, and then accidentally clicked ‘No’ when it asked me if I wanted to save the file. Arg. Important notes lost…

But I found the answer. The plugin called Autosave will save these new (AKA untitled) files every X minutes, or when Notepad++ looses focus, or both.

You can get Autosave here:
http://sourceforge.net/apps/mediawiki/notepad-plus/index.php?title=Plugin_Central#A
or here:
https://sites.google.com/site/fstellari/nppplugins

Then figure out if you’re using the Unicode or ASCII version of Notepad++ by navigating to the menu bar in Notepad++, clicking the “?” and then going to “About Notepad++”. Most likely you’ll be running the Unicode version. In that case you’ll use the AutoSaveU.dll.

After you know your Notepad++ flavor, grab the respective dll and place it in your plugins folder under the Notepad++ folder. For me this is:
C:\Program Files (x86)\Notepad++\plugins

Then restart Notepad++ and modify the options by going to the Notepad++ menu bar and navigating to Plugins->AutoSave->Options.

I like my AutoSave configured to the following:

What many of you probably know is that you can chain commands together with the semicolon. Like so:

So here we’re running a unixbench, and then directly after, we’re appending “unixbench finished” to unixbench.log.

But what you might not know about is the ‘&&’ replacement for ‘;’. This will only do the next command if the first command returns 0, meaning clean finish.

And taking it a step further, there’s ‘||’ which does the opposite of ‘&&’. If the first command fails, then the next command happens.

 

As of the Hyper-V Version: 6.2.9200.16384, Ubuntu 12.04 x86_64 performs very slow as a guest os. I switched to CentOS 6.2 x86_64 and performance was dramatically increased. It should be noted that “Linux Integration Services Version 3.4 for Hyper-V” was installed on the CentOS system, but not the Ubuntu system. I’ll investigate this at a later date.

I’ll post a unixbench of both VMs when I get a maintenance window. But for now, examine these load averages. Both running a minecraft server (Bukkit 1.4.6-R0.1) of the same world with the same amount of people. Both had 4GB of ram and 4 CPUs.

Ubuntu 12.04 x86_64: load average: 2.65, 2.92, 2.47

CentOS 6.2 x86_64: load average: 0.14, 0.11, 0.09

—————————–

EDIT 12/27/2012

UnixBench Ubuntu 12.04

UnixBench CentOS 6.2

If you have a sudo command you’re trying to run at startup in your /etc/rc.local on a CentOS system, it might not work. The reason is the following error that’s buried in the /var/log/boot.log file:

It might be hard to find, but you can always add a ‘sleep 30’ before your sudo command in your /etc/rc.local. This way, the message will show up at the end of the boot.log

Anyhow the reason this is happening is for security. To allow sudo on boot, run ‘visudo’ as root and comment out ‘Defaults requiretty’ as seen below:

Now your sudo command should run just fine at boot time.

——————————

Here’s an example of why you might want to run sudo at boot.

In the above command, I’m running the script startMinecraft, as the user minesrv. startMinecraft has some screen magic, and I want it tied to the minesrv user.

Here’s how you start up a GNU screen session at startup and give it a command to run.

So in this case we’re starting a minecraft server in a screen session.

Per the man page -dm does the following:

the -S gives the screen session a name so it’s easier to find later on.

Then it runs the command, java, with its parameters.

———————————————————————————

Another useful tool is sudo, so we can run our above startup script as a different user than root.

startMinecraft is the first bash script above. Here we’re using sudo to run it as the user ‘minesrv’.

The -i makes sudo perform all the standard login processes before running the script.

—————————————————————-

And finally, you can just reference the startup script inside /etc/rc.local for most linux distros. That will make the script run at startup.