Debian Package of the Day (static archived copy)

Article submitted by Kris Marsh. If you celebrate Christmas, you can give to Debian Package of the Day a nice present: a good article! :-)

Ever wanted to monitor a directory every second and see differences in filesizes per second? Or for that matter, run any program once a second and highlight differences in time? Well you can, and you have been able to since forever as it’s installed by default on the majority of Linux distributions. watch is part of the procps package, available in Debian and Ubuntu.

Here is an example for checking a directory:

watch ls -l

To highlight changes in each program run, you can use the -d flag:

watch -d ls -l

And to run the command every N seconds, use -nN (by default, watch runs every 2 seconds):

watch -n1 -d ls -l

Finally, to make the diff highlighting “sticky” (i.e. stay on permanently after a change is detected), use: -d=cumulative

Other examples:

• Watch your log directory for changes

  watch -d=cumulative -n1 ls -lt /var/log

• Watch for new email

  watch -n60 from

• Monitor free memory

  watch -n10 free -m

• Monitor established connections

  watch -n1 -d 'netstat -an | grep ESTABLISHED'

… you get the point. If you’re a system administrator, or just maintain Linux machines in general you’ll probably spot a bunch of places where you can use this straight away.

Article submitted by David A. Thompson. We’re running out of articles! If you like Debian Package of the Day please submit good articles about software you like!

Grumble… a postgresql server on an old Sun workstation isn’t visible to another old Sun workstation which (in theory…) is storing data on the postgresql server. The culprit was a misconfigured firewall. Rather than wading through a bunch of iptables commands, it seemed time to revisit the world of iptables front-ends on the off-chance there was an undiscovered treasure I’d missed on earlier visits. It turns out that there was one: ferm.

A revisit to firestarter, a straightforward GUI interface, ended when firestarter segfaulted and then, when started again, automatically started its firewall. Fortunately, I had altered the firestarter rule set and opened port 22 before firestarter segfaulted. Otherwise I would have been hundreds of miles away from an inaccessible server. After firestarter crashed again with a memory error, I decided to move on…

Like several other firewall front-ends, ferm is aware of the issues associated with working on servers hundreds of miles away from one’s physical location. Ferm starts with a default configuration which leaves the default SSH port open. Even better, ferm has a ‘try-before-you-buy’ feature (shared with a few other packages such as firehol): ferm --interactive activates a specific ruleset and, if a user response isn’t given within 30 sec, the system reverts to the previous ruleset.

Rather than using a GUI interface (e.g., firestarter, gnome lokkit, guarddog, kmyfirewall, knetfilter, …), ferm is configured via a text configuration file and can be controlled in a straightforward manner from the console. This may be a desirable feature for running on a box with limited disk space as GUI interfaces generally require the presence of X windows-related packages, often along with several KDE- or Gnome-related packages.

My main concern wasn’t with whether the application had a GUI or console interface but was with whether the application facilitated straightforward configuration of an iptables ruleset (translation: it shouldn’t take 20 min of reading documentation to get a simple firewall up). Other front-ends (e.g., shorewall and firewall builder) appear to be designed for complex rule-sets and require a substantial investment of effort to learn the syntax of configuration files or a ‘rule-making language’.

Along with ferm, another front-end, firehol seemed to also hit the mark with respect to having a straightforward syntax. Unfortunately, I found that firehol ended up being a time-consumer. In my experience, preparing a firehol configuration file which didn’t trigger multiple errors from firehol/iptables did not prove to be straightforward. In contrast, ferm gave me no such problems. A few tweaks of the default system configuration file —primarily opening a few ports—:

  proto tcp dport ssh ACCEPT;
  proto tcp dport http ACCEPT;
  proto tcp dport https ACCEPT;
  proto tcp dport postgres ACCEPT;

A simple /etc/init.d/ferm restart and things were running smoothly. Minimal effort, satisfying results…

The bottom line is that, for simple rulesets, using ferm is definitely easier than preparing iptables rules by hand. However, ferm can also be used to put together more complex firewall rulesets. It uses a reasonably powerful configuration language (including support for variables, function definitions, and arrays) which facilitates addressing more complex situations than the one I faced. To top it off, ferm seems to be under active development with bugs being squashed and features being added relatively regularly.

ferm has been available in Debian since Etch and in Ubuntu since Dapper.

Update, editor’s note: I’d like to add to this article my personal experience with ferm. Being a SysAdmin, I’ve been using netfilter/iptables for many years, after migrating away from ipchains; and the day I’ve found ferm my work changed completely. To me, being able to write your rules in clean structures, with blocks, variables and ‘functions’ is, by far, the most important feature of ferm. Thanks to this, I was able to write very complicated rule-sets, which were still readable to the point that the more junior SysAdmins, with little exprience on netfilter, have no difficult modifying it to open up ports or creating a new NAT rule.

Having said that, a warning to the newcomers to netfilter: there’s no tool that will magically allow you to write non-trivial rule-sets if you don’t understand the underlying stuff. You will be able to manage your home server, but if you want to do more serious work, you’ll need to really understand how TCP/IP works, and after that, read a lot about the details of routing and packet filtering in Linux. Having seen many people get frustrated by this, is better for you to know that this beast is quite tricky.

Article submitted by Raman Pandarinathan. We’re running out of articles! If you like Debian Package of the Day please submit good articles about software you like!

As a parent, have you ever wondered if kids can use FOSS to have fun and learn at the same time? As a teacher, have you ever wondered how to teach using a computer and FOSS tools? The answer is gcompris.

Gcompris combines fun and learning. Each activity is designed and developed with creativity in mind, and it has a nice interface for children.

My children have learned some computer basics like mouse usage, it has also helped them to understand basic arithmetic, colour identification and many other things. Tuxpaint is also included, so children can draw to their imagination.

Gcompris is a collection of over 90 educational activities for children. The activities are classified into mathematics, computer discovery, puzzles, strategy games, amusement activities, experimental activities and reading activities.

Mathematics

This has more than 20 activities classified into calculations, geometry and numeration. The activities are planned to teach basic arithmetic, geometry, money usage, etc.

For example, below you can see a screen shot of an activity that consist in finding series of numerical operations. Here the final answer is 15 and should be derived in two steps. The child has to select the numbers and operators from the top and form equations to get the final answer.

Puzzles

The puzzle activities include: drag and drop pieces to rebuild paintings, build a given shape with seven pieces, drive the crane and copy the model, tower of Hanoi, sudoku and the fifteen game.

Below is a screen shot of the Crane activity. The objects in the left grid should be placed in the same position as in the right side grid. The crane can be operated by clicking on the four arrows at the bottom.

Computer discovery

These activities help children learn basic skills of computers. Bellow is a screen shot of the keyboard activity in which the child has to push the ball to Tux. In order to do it, both shift keys should be pressed simultaneously, as if pushing the ball with the hands. If they are pressed simultaneously the ball will travel in a straight line and reach Tux, if not the ball will drift and fall into the sea.

Strategy Games

Some of them are chess, arranging four coins in a row, bar game (don’t use the last ball), and oware (shown below).

Amusement Activities

The amusement activities include Tuxpaint, a simple football game, and an animation creator.

Below is a screen shot of the animation creator. If you want to create an animation, you first select an image and put it somewhere. Then take a snapshot using the camera icon. Now move it to the next position and take another snapshot. Repeat until you reach the desired position. Finally click on the film icon and you’ll see the animation.

Experimental activities

This section lets the children learn various things which require thinking in a series of steps. Things like the water cycle and operating canal lock lets the child learn systemic thinking.

Below is a screen shot of the activity about the water cycle. First the sun raises, water evaporates and clouds are formed. When you click on the cloud it starts raining and the rain fills the water tank. Operating the water inlet gives Tux a shower.

Discovery

This section is about learning several common things like colour names, clock reading, symmetry, etc. The activity shown in the screen shot is about identifying colours: you must identify the colour from the name displayed.

Reading Activities

These are activities about learning the letters, words and matching them with images. Reading can be practised both horizontal and vertical.

Below is a screen shot where the child has to drag and drop the image onto the correct name.

As part of my Linux Users Group activity, I give talks and demos about FOSS frequently. Whenever I see kids and parents among the audience, the first thing I do is to demonstrate gcompris, and it’s a sure hit. The kids love it and parents realize its educational value.

Here are some photos of one such event held in a public park at Chennai, India.

Pros and cons

• Pros
• Very well designed activities.
• Parental touch.
• Lot of activities.
• Translated to more than 40 languages.
• Cons
• It requires more local language and sound support, especially for several Indian languages. At present for Indian Languages the sounds and reading practices are not well developed. Though gcompris is well structured to support translations, it lacks volunteers.

There is another similar package named childsplay - also available in Debian.

Availability

gcompris was a part of Debian even in the Sarge days and it’s been in Ubuntu since Dapper (if not before!).