Preface: legal stuff
Depending on where you live, use of random open wifi networks might be considered illegal. Although I know of no law in my country against doing this, where you live, things may be different, so educate yourself before following my example.
Wifi roaming on the move
For the past year I have used my Eee PC on the metro transit bus, as it is the perfect size for this. When I can, I take advantage of open networks to connect back home. In this article I will show how you can actually use such access, will recommend which software works best and will explain how to set it up.
So, what can I really do with the net while in motion?
How about irc? No kidding! This shell one-liner does the job:
while ! ssh -t 10.9.8.7 'screen -UDr' 2>/dev/null ; do echo -n "." ; sleep .1 ; done
We’re concerned about privacy and security on other people’s networks, so we use ssh. Inside that screen session, keep irssi running for a continuous irc presence. Every 10th of a second, the script tries to resume your session. Once a the net passes by, typing “[Enter]~.” drops you back out to retry again. The row of dots serves as a progress bar. If you want to get fancy, you could replace that with an
ASCII ‘spinner’. I leave that as an exercise for the reader. :)
Come on, is that really usable?
Certainly. As the good folks on #eeepc at irc.freenode.net and #debian-eeepc at irc.oftc.net can attest, even a half dozen brief connections can be enough to provide tech support, rough out some development ideas, or just carry on some friendly chat. If your spouse or housemate is online too, it can even help you make some last-minute grocery-list changes. :) While the script is working, enjoy some offline things such as blogging, reading a cached Planet Debian feed or a
PDF book.
OK, so what else do I need to make it work?
Well, you’ve seen so far we need on a server:
- openssh-server
- screen
- irssi
On the Eee, you should also have:
- openssh-client
- wpasupplicant
- gnome-terminal
But what do I need wpasupplicant for if I only use open networks?
Well, wpasupplicant is really handy for fast control of networks in Roaming Mode (as per /usr/share/doc/wpasupplicant/README.modes.gz).
A GUI is just too slow. For example, you may need to filter out ‘junk’ open wifi nets: pay-per-use hotspots or nets that hide their name. You’ll not only want a “catch-all” stanza for any open network, but also a number of the most commonly found default network names, e.g.
# Catch-all; associates with any open network:
network=
key_mgmt=NONE
# Commonly found default network names:
network=
ssid="default"
key_mgmt=NONE
network=
ssid="linksys"
key_mgmt=NONE
# etc. by watching scan_results closely you'll find several more
While the connect script is running, keep a separate tab open in gnome-terminal for wpa_cli. Use ‘disable_network 0’ to drop the catch-all and let the other stanzas kick in and ‘enable_network 0’ after filtering is no longer needed.
Isn’t it really slow to get connected?
Without some tweaks, yes. But here are a few things I have found by trial and error that help.
One issue is that dhclient takes too long to retry, so you drop the delay between retries back to 1 second in /etc/dhcp3/dhclient.conf:
backoff-cutoff 1;
initial-interval 1;
If the signal is very weak, you’ll want the transmit power turned up to the maximum value for your hardware. For the Eee
PC 4G this is 50mW, so you set this in /etc/network/interfaces for ath0, your wireless interface:
wireless-txpower 50mW
Finally, while you’re in motion you are constantly leaving no-longer-usable access points behind. The driver needs to discard them as quickly as possible and scan for new ones. So again in /etc/network/interfaces for ath0, you bring the default scanvalid 60 seconds down to 10 with:
pre-up /sbin/iwpriv ath0 scanvalid 10
Conclusion
The netbook has changed how we use the net. Now that we can take it everywhere, we either pay through the nose for expensive cell network access or else use the patchy wifi coverage blanketing most urban areas. A few lucky cities have such things as municipal wifi nets, but the rest of us have to scrape what access we can wherever we go. You are now equipped to try this out on the bus. If you find any other tips that can help, I’d love to hear from you.
Nagios has the - very useful - feature of “parent hosts”. If it deems a host A being down, it first checks
its parent host, B, and reports A only as down if B is up. This goes back recursively until a host with state
“up” is found and only the first “down” host is actually reported. This keeps on-call people
from being bombed with alerts in case of major network outages and makes sure that the alerts that are actually sent out
do reasonably accurately describe the actual outage.
As an individual who has some “external” servers in various data centers on the Internet, I would like to
not be alerted multiple times that my servers at ISP C, D, and E are down if there is an outage at the ISP F hosting my
Nagios installation or at one of the various exchange points temporarily rendering the servers unreachable (without me
being able to do anything).
The solution sounds easy but is surprisingly hard.
How one could solve the issue
For each host in the manual nagios configuration, do a traceroute and generate host stanzas for each of the hosts
found:
The following list is merely a small selection of scholarly articles
listed in the 
Recently I've been hacking around on GNU screen. I've fixed a few bugs and added a few new features. One of the earliest features I added was the ability to source every file in a directory. One of 
After my 
While it's a protocol we all love to hate, and wish it would go away and
die a quiet death, sometimes someone has a good reason for supporting FTP.
(In my case, it's usually because that reason has a lot of money to
provide to my employer). But what if you want your FTP servers load
balanced (because downtime is for suckers)?
Obviously, you need to have some sort of shared filesystem behind all your
load balanced FTP servers, but that's a rant for another day (but let me
just say: if you're running GFS, especially on a busy site, may
$DEITY have mercy on your soul).
Because of the silly random port games that FTP likes to play, it's not a
trivial job to load balance an FTP service amongst multiple hosts. You
can't just throw a round-robin on port 21 and hope to get anything useful
going.
Ironically, while "active" FTP is a pain in the arse for most people, it's
a lot easier to load balance, because the initial connection comes in on a
well-known port which can be load-balanced, while all the other "random"
connections are server-initiated and your standard routing/NATing/whatever
you're doing for outgoing connectivity should be able to handle it.
However, passive FTP is a bigger pain. The problem is pretty simple to
understand -- the FTP client will want to connect to a high port on the
"virtual" (load-balanced) IP, and without serious traffic sniffing, your
load balancer won't be able to map that incoming connection on port 54321
to the real server that actually wanted the connection.
The solution, thankfully, is fairly straightforward. You allocate a range
of high ports (maybe a thousand or so) to each real server, with a
different port range for each real server. You then tell the load
balancer to send all traffic for each range of ports to the corresponding
real server, and then configure that real server to put all it's passive
connections into that port range (I'm fairly sure most FTP servers can
support that bit of config).
So, unfortunately, you can no longer disallow FTP support on the basis
that you can't load balance it. No shortage of other reasons, though.
Wow this Joe the Plumber phenomenon really seems to have Democrats spooked as they are now scrambling to find 
As some of you know, the first weekend in October was a big deal for me,
because it was
As a beta tester for the new email application from Nokia, you will have to give your mail account password:
