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Subsections
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.
Let's go through each of these steps in a bit more detail.
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.
Deciding what to do with config files:
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!
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.
Next: Performing an Install
Up: Using RPM to Install
Previous: Using RPM to Install
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