The basic idea of RPM is that you have a database of packages and the files that belong to a package. When you install a new package, the information about this package is recorded in the database. Then, when you want to uninstall the package, for every file of the package, RPM checks whether there are other packages installed using this file, too. If this is the case, the file in question is not deleted.

In addition, RPM tracks dependencies. Each package can be dependent on one or more other packages. When you install a package, RPM checks whether the packages the new package is dependent on are already installed. If not, it informs you about the dependency and refuses to install the package.

The dependencies are also used for removing packages: when you want to uninstall a package that other packages are still dependent upon, RPM tells you about this, too, and refuses to execute the task.

The increased convenience of using RPM packages comes at a price, however: First, as a developer, it is significantly more difficult to make a RPM package than to simply pack everything in a tar archive. And second, it is not possible to retrieve just one file from a RPM package; you have to install everything or nothing.

If you already have an RPM system, installing RPM packages is very easy. Let's say that you have a RPM package called SuperFrob-4.i386.rpm (RPM package always have the extension .rpm; the i386 indicates that this is a binary package compiled for Intel machines). You could then install it with:

tigger # rpm -i SuperFrob-4.i386.rpm

Instead of -i, you can also use the long-named version of this option; choose whatever you like better:

tigger # rpm --install SuperFrob-4.i386.rpm

If everything goes well, there will be no output. If you want RPM to be more verbose, you can try:

tigger # rpm -ivh SuperFrob-4.i386.rpm

This prints the name of the package plus a number of hash marks, so that you can see how the installation progresses.

If the package you want to install needs another package that is not yet installed, you will get something like the following:

tigger # rpm -i SuperFrob-4.i386.rpm
failed dependencies:
        frobnik-2 is needed by SuperFrob-4

If you see this, you have to hunt for the package frobnik-2 and install this first. Of course, this package can itself be dependent on other packages again.

If you want to update a package, use the -U or - -update option (which is just the -i option combined with a few more implied options):

tigger # rpm -U SuperFrob-5.i386.rpm

Uninstalling a package is done with the -e or --erase option. In this case, you do not specify the package file (you might not have that around any longer), but the package name and version number:

tigger # rpm -e SuperFrob-5

Besides the options described so far that alter the state of your system, the -q option provides various kinds of informations about everything that is recorded in the RPM database as well as package files. Here are some useful things you can do with -q:

• Find out the version number of an installed package:

  tigger# rpm -q SuperFrob
  SuperFrob-5

• Get a list of all installed packages:

  tigger# rpm -qa
  SuperFrob-5
  OmniFrob-3
  ...
  libc-5.4.47-1

• Find out to which package a file belongs:

  tigger# rpm -qf /usr/bin/dothefrob
  SuperFrob-5
  tigger# rpm -qf /home/kalle/.xinitrc
  file /home/kalle/.xinitrc is not owned by any package

• Display information about the specified package:

  tigger# rpm -qi rpm 
  Name        : rpm                Distribution: SuSE Linux 5.2 (i386)
  Version     : 2.4.12             Vendor: SuSE GmbH, Fuerth, Germany
  Release     : 3                  Build Date: Tue Mar 10 01:35:47 1998
  Install date: Fri Sep 25 18:43:41 1998 Build Host: Pascal.fs100.suse.d
  Group       :                    Source RPM: rpm-2.4.12-3.src.rpm
  Size        : 1163708
  Packager    : feedback@suse.de
  Summary     : rpm - Red Hat Package Manager
  Description :
  rpm (Red Hat Package Manager) is the main tool for managing software 
  packages of the SuSE Linux distribution. rpm can be used to install
  
  and remove software packages; with rpm it's easy to update packages.  
  rpm keep track of all these manipulations in a central database. This 
  way it is possible to get an overview of all installed packages; rpm 
  also supports database queries.

• Show the files that will be installed for the specified package file:

  tigger# rpm -qpl SuperFrob-5.i386.rpm
  /usr/bin/dothefrob
  /usr/bin/frobhelper
  /usr/doc/SuperFrob/Installation
  /usr/doc/SuperFrob/README
  /usr/man/man1/dothefrob.1

What we've just finished showing are the basic modes of operation, which are supplemented by a large number of additional options. You can check those in the manual page for the rpm command.

If you are faced with a RPM package that you want to install, but have a system like Slackware or Debian that is not based on RPM, things get a little bit more difficult.

You can either use the fairly self-explanatory command alien that can convert between various package formats and comes with most distributions, or you can build the RPM database from scratch.