Archive for January, 2011

Bridging Tweaks for libvirtd on Ubuntu Desktop 10.10

Having recently dual-booted my main desktop system with Ubuntu 10.10 64-bit, I decided to setup virt-manager to handle KVM virtual machines.  While I don’t have a current use for VMs other than to play around with things as I run into them, I wanted them to be able to talk to other physical machines on my network w/o adding another hop into my internal network.

Therefore, I needed bridging such that virtual machines were assigned IPs (statically or dynamically) in the same subnet as my main desktop. To do this, I followed steps 2.1 and 2.2 from KVM Networking – Community Ubuntu Documentation guide.

Once I did this, everything seemed happy.  However, I noticed that the default bridged network of 192.168.1.x and the default bridge interface virbr0 were still being created, even after restarting libvirtd.  Additionally, this was causing dnsmasq to be started on the system.  With the bridging method I’m using,  there’s no need for that since the virtual machines can reach the name server on my network.  A little more research showed that essentially both problems here were the result of the symlink /etc/libvirt/qemu/networks/autostart/default.xml . Once I removed that, libvirtd was no longer using them, but it hadn’t shut them down.  A little brctl and kill love and all was well again in the universe. :)

Purple Notebook 78

Saw, stitch, mend, fix
The mind can play so many tricks
Some behaviors feel so deeply engrained
Unrelenting like the monsoon rain
But it’s all a matter of perception
Reality defined by an idea’s conception
Can’t buy a vegetable spray
That will unstick a viewpoint’s way
Only the heart balanced with the mind
Can free us from the emotional rut we grind

Purple Notebook 77

I want to tell you I miss you
But that would just make it worse
I want to hold you and kiss you
And tell you everything will be OK
But that won’t be happening tonight
Or any other night
But still I
Can’t help

Using Munin to Monitor My Comcast Cable Modem

Over the last 6 months or so, I’ve had problems with my Comcast Internet service intermittently cutting out every so often.  As the end user, what I’ve noticed is packet loss,  sometimes it’s a small amount over a short amount of time (minutes), others a large amount over a long amount of time (hours).  Initially the issues were few and far between, so I didn’t give it much notice.  However in the last month or so, it’s become a lot worse (once or twice a week).

I had initially setup Smokeping to monitor when problems started happening.  I had it ping the inside IP of my router, the private IP of the cable modem and the next hop route my router is given in it’s DHCP lease.  It helped me make sure the cable modem was up when I started having packet loss.

While this was nice to know when it was happening, it doesn’t really give you any data that helps with the why.  When I would call Comcast Tech Support, they could confirm the levels on my cable modem weren’t in desirable parameters, but I didn’t get the feeling the knew what they were (or recording them).  Then last week I ran into Jeff Forman’s post about how he was monitoring the signal to noise ration with a custom Munin plugin he had written.

Since I had just started playing with Munin and was looking for a coding type project to work on, I decided to bust out my horribly rusty Perl skills and write my own plugin.  Now I have purdy graphs that look like:

In case this plugin might be useful to you, I’ve made it available here at Github.

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