alien is a program that converts between Red Hat rpm, Debian deb, Stampede slp, Slackware tgz, and Solaris pkg file formats.

Install alien
First check if alien is installed

roshan@ubuntuWorkerB:~$ alien
The program ‘alien’ is currently not installed. You can install it by typing:
sudo apt-get install alien
-bash: alien: command not found

Since alien is not installed, use the following command to install it

roshan@ubuntuWorkerB:~$ sudo aptitude -y install alien
roshan@ubuntuWorkerB:~$ alien
You must specify a file to convert.

Usage: alien [options] file [...]
file [...] Package file or files to convert.

Using alien

If you have an rpm package, you can convert it to a debian (deb) package using the following command:

roshan@ubuntuWorkerB:~$ sudo alien -kc appistry-cloudiq-4.2.1.2-rhel5.rpm 
appistry-cloudiq_4.2.1.2-rhel5_i386.deb generated