To get the network address perform a bitwise AND on the IP address and the netmask:
network = ip & netmask

To get the broadcast address perform a bitwise OR on the network address and the complement of the netmask:
broadcast = network | ~netmask

Here a simple C program you can use to calculate the network and broadcast addresses on your own:

#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
    struct in_addr ip;
    struct in_addr netmask;
    struct in_addr network;
    struct in_addr broadcast;

    if (argc != 3)
    {
        printf("usage: %s ip netmask\n", argv[0]);
        exit(0);
    }   

    inet_aton(argv[1], &ip);
    inet_aton(argv[2], &netmask);

    // bitwise AND of ip and netmask gives the network
    network.s_addr = ip.s_addr & netmask.s_addr;
    printf("network %s\n", inet_ntoa(network));

    // bitwise OR of network and complement of netmask gives the broadcast
    broadcast.s_addr = network.s_addr | ~netmask.s_addr;
    printf("broadcast %s\n", inet_ntoa(broadcast));

    return 0;
}

To compile it use the command:

gcc -Wall ipcalc.c -o ipcalc

The usage is really simple:

$ ./ipcalc
usage: ./ipcalc ip netmask
$ ./ipcalc 192.168.1.0 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255

Feel free to use it and send me comments/suggestions

I suppose this happens because VMWare preallocates space to improve the performance of IO operations. If I try to compress the image as it is the compression ratio will be really low. The reason is that the preallocated free space contains random data that is hard to compress. If we could fill this free space with a repeating pattern then we could achieve a much higher compression ratio.

The solution I found online is really simple and works. By running the following command we fill the extra space with zero bytes:

cat /dev/zero > zero.fill; sync; sleep 1; sync; rm -f zero.fill

After running the command I used gzip to compress the image to 178MB from 1.2GB!

Update: Debian Lenny 5.0 now has support for the option autoremove of apt-get that is able to clean all unused dependencies

Curiosity and laziness are the two most important reasons that my system ends up with lots of useless software after a couple months of usage. Many times I want to test drive a program and if it suits my needs I’ll keep it otherwise it will end up in /dev/null.

With apt-get magic it is amazingly easy to install lots of programs in seconds. The problem comes when you want to get rid of them because each program comes with a list of dependencies that get installed automatically for you. So you have to keep a list of the dependencies to be able to uninstall them when you don’t need the program anymore. I used to copy the dependencies from the apt-get confirmation screen to a text file so that I can remove them later. That didn’t work for me, thus I had to find a way to do it automatically.

I created two scripts that use Debian tools to create a checkpoint before I install a new program and then rollback to that state when I don’t need that program anymore. The first script is named dpkg-backup because it creates a backup copy of the installed packages list. Here it is:

#!/bin/sh
# dpkg-backup.sh

dpkg --get-selections > /tmp/dpkg-list.txt

The second script is named dpkg-restore because it restores the packages to the saved state. Source code:

#!/bin/sh
# dpkg-restore.sh

if [ -f /tmp/dpkg-list.txt ]
then
    /usr/bin/dpkg --clear-selections
    /usr/bin/dpkg --set-selections < /tmp/dpkg-list.txt
    /usr/bin/dpkg --get-selections | sed -e \'s/deinstall/purge/\' > /tmp/dpkg-list.txt
    /usr/bin/dpkg --set-selections < /tmp/dpkg-list.txt
    rm /tmp/dpkg-list.txt
    /usr/bin/apt-get dselect-upgrade
else
    echo "You must use dpkg-backup first."
fi

Usage is pretty simple. All you have to do is run dpkg-backup.sh before you install a program with apt-get. Then use apt-get to install it and when you want to get rid of it use dpkg-restore.sh and everything associated with that program is gone for good . An example usage scenario is provided below:

$ dpkg-backup.sh
$ apt-get install test-program
...
# After playing around with the program you realize that you don't need it anymore!
$ dpkg-restore.sh

That’s it! I hope you find these two scripts as useful as I did. By the way both are licensed as GPLv2 so feel free to modify and distribute. If you find any bugs or have any ideas/comments on how to improve them let me know!

Note: This post was written back when I used to have a Debian GNU/Linux machine as my desktop computer. The Debian version at that time was etch 4.0. Nowadays I have a new shiny MacBook Pro with Mac OS X Leopard that I use as my main work machine so some of the information in this page might be out-of-date or inaccurate.

Whenever I format my computer (and trust me that happens really often) I want only the programs I use to be installed and nothing else. I don’t like having my machine overloaded with crappy software that I never use (that’s the case with Microsoft Windows). So every time I have to remember which programs I want and install them one by one with apt-get. For that reason I decided to create a list with all the programs I need. In that way I can just copy – paste the list every time I format.

The following commands will create a very minimal desktop with only the packages I need installed. If you think those packages meet your needs then you might find these commands useful. I have tested them only with Debian GNU/Linux 4.0, they will probably work with other Debian based distributions like Ubuntu.

First, we install X.Org:

apt-get install xserver-xorg-video-vesa xserver-xorg-input-kbd xserver-xorg-input-mouse
xserver-xorg-input-synaptics xserver-xorg-input-evdev xorg

Then we remove two packages that are installed by the previous command and are unnecessary:

dpkg -P xserver-xorg-input-all xserver-xorg-input-wacom

Finally, we install the rest of the packages including the desktop environment (Gnome):

apt-get install gnome-core file-roller gcalctool gconf-editor gdm
xpdf-reader gnome-media gnome-system-monitor gnome-themes
gnome-volume-manager gtk2-engines libgnomevfs2-extra
xscreensaver gnome-power-manager gnome-utils msttcorefonts
alacarte alsa-utils less openssh-client mtr-tiny nmap pidgin
iceweasel

That’s all folks, enjoy your newly formatted, minimal system!