Table 2-1. rpm -i Command Syntax
Of the many things RPM can do, probably the one that people think of first is the installation of software. As mentioned earlier, installing new software is a complex, error-prone job. RPM turns that process into a single command.
rpm -i (--install is equivalent) installs software that's been packaged into an RPM package file. It does this by:
Performing dependency checks.
Checking for conflicts.
Performing any tasks required before the install.
Deciding what to do with config files.
Unpacking files from the package and putting them in the proper place.
Performing any tasks required after the install.
Keeping track of what it did.
Some packages will not operate properly unless some other package is installed, too. RPM makes sure that the package being installed will have its dependency requirements met. It will also insure that the package's installation will not cause dependency problems for other already-installed packages.
RPM performs a number of checks during this phase. These checks look for things like attempts to install an already installed package, attempts to install an older package over a newer version, or the possibility that a file may be overwritten.
There are cases where one or more commands must be given prior to the actual installation of a package. RPM performs these commands exactly as directed by the package builder, thus eliminating a common source of problems during installations.
One of the features that really sets RPM apart from other package managers, is the way it handles configuration files. Since these files are normally changed to customize the behavior of installed software, simply overwriting a config file would tend to make people angry — all their customizations would be gone! Instead, RPM analyzes the situation and attempts to do "the right thing" with config files, even if they weren't originally installed by RPM! [1]
This is the step most people think of when they think about installing software. Each package file contains a list of files that are to be installed, as well as their destination on your system. In addition, many other file attributes, such as permissions and ownerships, are set correctly by RPM.
Very often a new package requires that one or more commands be executed after the new files are in place. An example of this would be running ldconfig to make new shared libraries accessible.
Every time RPM installs a package on your system, it keeps track of the files it installed, in its database. The database contains a wealth of information necessary for RPM to do its job. For example, RPM uses the database when it checks for possible conflicts during an install.
| [1] | Are you interested in what exactly "the right thing" means? the section called Config file magic in Chapter 4 has all the details. |