mac9416.com

A couple of days ago, I had need to write a BASH script that would take a screenshot once a minute and save it for my later review. This is what I came up with:

while [ 1 ];
do
scrot ./`date +%F_%k.%M`.png;
sleep 60;
done

The script starts by creating never-ending while loop. The scrot command takes a screenshot and saves it in the current working directory as the current date and time (e.g. 2011-03-15_18.56.png). The sleep command causes the script to pause for 60 seconds before looping again.
This script will run indefinitely until it is killed (I run it in a terminal and kill it by hitting ctrl+c).

A while back, I blogged about how I connect to Verizon mobile broadband in Lubuntu. Now that I am connected, I have to worry about the monthly 5GB/month limit enforced by Verizon. In order to avoid the very high overuse fees, I must carefully monitor my bandwidth usage.

I’ve chosen the easy to set up vnstat to monitor bandwidth and vnstati to output the stats as an image. Installing vnstat and vnstati in Ubuntu is as simple as:

sudo apt-get install vnstat vnstati

Once vnstat is installed, I must tell vnstat to start monitoring my network interface. For my mobile broadband setup, the interface is ppp0.

sudo vnstat -u -i ppp0

After running that command, I rebooted to make sure the vnstat daemon was running.
Now vnstat is storing network usage information in a database. But how can one see this information in an easy-to-understand form? This command will output an image with a nice graph showing daily bandwidth usage:

vnstati -i ppp0 -o ~/vnstat.png -d

Of course, I don’t want to run that command every time I want to see up-to-date stats. So I create a cron job to run the command every five minutes by running

crontab -e

copying

0,5,10,15,20,25,30,35,40,45,50,55 * * * * vnstati -i ppp0 -o ~/vnstat.png -d

into the editor, and then saving the file.

Cron will immediately start doing its thing and within five minutes an up-to-date image will appear in the home folder.

For convenience, I have made file:///home/mac9416/vnstat.png my home page in Firefox. When I want to check the latest stats, I simply refresh the page.

A week ago, the concept of a Stack Exchange was completely foreign to me. I had used many traditional forums before, and I have been fairly active on Ubuntu Forums. But, excited to try something new, I committed to participate in the private beta of the proposed Ubuntu Stack Exchange.

Over the past week, I have asked three questions, answered twenty-one questions (four were accepted), and earned over seven hundred reputation points. I’ve added a sidebar widget to promote the Exchange and show off my stats.

I have learned that the biggest difference between an Exchange and a forum is the intensity level. A forum is very laid-back because there is not much at stake. If you write a bad question or answer, people simply ignore it. Unless you are obnoxious, you’ll do just fine.
On a Stack Exchange, you are awarded for your good effort and punished for your lack of it. This makes stepping on toes inevitable, but in my opinion it makes for a more productive community.

It’s a trade-off, and there will be many people using both. I’ll continue to use both for the foreseeable future, though I’ll probably start asking more questions on the Exchange than the Forums.

The public beta begins in ten minutes, so go over to the Ubuntu Exchange and try it for yourself!

About a week ago, I mustered up the courage to replace Ubuntu 9.10 on my laptop with lubuntu 10.04. Overall, the transition was quite smooth. The biggest problem I encountered was not being able to connect to Verizon mobile broadband with my PC5750 card.

A few days before I installed lubuntu, I had read on the Keryx forums that someone had similar trouble in Ubuntu Studio 10.04. They solved it by installing the latest usb-modeswitch and usb-modeswitch-data packages from the Debian repositories. This was, of course, the first thing I tried. But there was no apparent improvement; the Network Manager applet still failed to show the device.

So I went to UbuntuForums with the problem. One kind soul pointed me to a 3G tutorial on backtrack-linux.org. My first attempt to follow the directions was successful. But I was unable to do it again the next day.

In desperation, I decided to learn how to connect to my device “by hand” with GnomePPP and, later, wvdial. That is what you are about to learn how to do.

Gathering Materials

You will, of course, need a Verizon USB or PC card modem. Mine happens to be an Audiovox PC5750.

As for software, you will need either GnomePPP or wvdial. Neither come with lubuntu 10.04, so I had to install them with Keryx. If you only plan to use the command line to connect, you’ll only need wvdial.

Finding Your Modem’s Device Path

Both GnomePPP and wvdial will need the device path of your modem. To find it, remove the modem and plug it back in. Then open a terminal and run dmesg.

$ dmesg

Towards the end of the output, you will see some messages indicating that a device has been detected. The output will include a device path starting with “/dev/”. Mine is “/dev/ttyACM0″.

Connecting With GnomePPP

Now that you have GnomePPP installed and your modem’s device name written down somewhere, you can start connecting.

Hit <alt><F2> or open up a terminal and run ‘gksu gnome-ppp’.

After providing your password, you will see a simple dialog where you will enter your connection information. Enter ‘none’ in the Username and Password fields. (Apparently they are required, but have no effect on the connection.) If you’d rather not have to type “none” in the password field next time you connect, check “Remember password.” Then enter #777 in the number field. I’m not sure why that is the number. It just is.

Now you’ll need to give GnomePPP some details about your device. First click the Setup button. At the top of the window that appears, there will be a Device field. Enter the device path you found earlier (again, mine was /dev/ttyACM0). Next, click the device Type dropdown and choose USB Modem.

That’s all the advanced configuration you’ll need. Click “Close,” and then click the Connect button. After about ten seconds, you will be given a friendly prompt announcing that you are connected, and a timer will start counting the time you remain connected.

One more thing you should look at is GnomePPP’s connection Details window. On the connection timer dialog, click “Details.” In the Details window you’ll find some very useful information. Most important to me (and I suspect many Verizon customers) is the bandwidth usage. Since Verizon enforces a 5GB per month bandwidth cap, it’s important to keep an eye on that number.

Connecting With wvdial

wvdial is the command-line tool that GnomePPP acts as a wrapper for. Using a command-line tool will allow you to create a connection script so you won’t have to open GnomePPP when you want to connect.

Once you have wvdial installed, you need to create a configuration file to give wvdial the information it needs to connect. Pop open your favorite text editor and enter this information:

Modem = <your device>
Phone = #777
Username = none
Password = none

Replace <your device> with the device path you found earlier. Mine reads “Device = /dev/ttyACM0″.

Save the new configuration file in your home directory as wvdial.conf.

Connecting is as simple as running one command.

$ sudo wvdial --config=$HOME/wvdial.conf

After about ten seconds, it will tell you that it’s connected and list a slew of IP addresses.

If you are, like me, too lazy to run the command to connect every time you start the computer, you can create a script to do it for you. Just open your text editor again and add the following lines.

#!/usr/bin/sh
gksu 'wvdial --config=wvdial.conf'

Then save the file to your desktop as “VerizonConnect”. Edit the file properties with your file manager or run the following command to make it executable.

$ chmod +x $HOME/Desktop/VerizonConnect

Now when you start the computer, all you have to do is double-click the script on the desktop and provide your password. Remember to give it a few seconds to connect before trying to load anything in your browser.

That’s it! You now know how to connect to your Verizon PC5750 (or similar) device in Ubuntu 10.04 with either GnomePPP or wvdial. If you have any questions, corrections, or requests for clarification, please leave a comment!

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