that provide low-level structure for a Linux distribution. Let's see what installed packages make up the Base group:

# rpm -qg Base

setup-1.5-1

pamconfig-0.50-5

filesystem-1.2-1

crontabs-1.3-1

dev-2.3-1

etcskel-1.1-1

initscripts-2.73-1

mailcap-1.0-3

pam-0.50-17

passwd-0.50-2

redhat-release-4.0-1

rootfiles-1.3-1

termcap-9.12.6-5

#

One thing to keep in mind is that group specifications are case sensitive. Issuing the command rpm -qg base won't produce any output.

RPM provides extensive support for dependencies between packages. Basically, a package might require what another package provides. The thing that is required and provided can be a shared library's soname (which is used to determine compatibility between different versions of the library). It can also be a character string chosen by the package builder. In any case, it's important to be able to display which packages provide a given capability.

This is just what the --whatprovides option does. When the option, followed by a capability, is added to a query command, RPM will select the packages that provide the capability. Here's an example:

# rpm -q --whatprovides module-info

kernel-2.0.18-5

#

In this case, the only package that provides the module-info capability is kernel-2.0.18-5.

The --whatrequires option is the logical complement to the --whatprovides option described earlier. It is used to display which packages require the specified capability. Expanding on the example we started with --whatprovides, let's see which packages require the module-info capability:

# rpm -q --whatrequires module-info

kernelcfg-0.3-2

#

There's only one package that requires module-info: kernelcfg-0.3-2.

5.2.2. Querying Commands, Part II: Information Selection

After specifying the package (or packages) you wish to query, you'll need to figure out just what information you'd like RPM to retrieve. As you've seen, by default RPM only returns the complete package label. But there's much more to a package than that. Here, we'll explore every information selection option available.

Adding -i to rpm -q tells RPM to give you some information on the package or packages you've selected. For the sake of clarity, let's take a look at what it gives you and explain what you're looking at:

# rpm -qi rpm

Name        : rpm                       Distribution: Red Hat Linux Vanderbilt

Version     : 2.3                             Vendor: Red Hat Software

Release     : 1                           Build Date: Tue Dec 24 09:07:59 1996

Install date: Thu Dec 26 23:01:51 1996    Build Host: porky.redhat.com

Group       : Utilities/System            Source RPM: rpm-2.3-1.src.rpm

Size        : 631157

Summary     : Red Hat Package Manager

Description :

RPM is a powerful package manager, which can be used to build, install, query,

verify, update, and uninstall individual software packages. A package

consists of an archive of files, and package information, including name,

version, and description.

#

There's quite a bit of information here, so let's go through it entry by entry:

• Name—The name of the package you queried. Usually (but not always) it bears some resemblance to the name of the underlying software.
• Version— The version number of the software, as specified by the software's original creator.
• Release—The number of times a package consisting of this software has been packaged. If the version number should change, the release number should start over again at 1.

As you've probably noticed, these three pieces of information comprise the package label we've come to know and love. Continuing, we have these:

• Install date—This is the time when the package was installed on your system.
• Group—In our example, this looks suspiciously like a path. If you went searching madly for a directory tree by that name, you'd come up dry—it isn't a set of directories at all.

  When a package builder starts to create a new package, he enters a list of words that describe the software. The list, which goes from least specific to most specific, attempts to categorize the software in a concise manner. The primary use for the group is to enable graphically oriented package managers based on RPM to present packages grouped by function. Red Hat Linux's glint command does this.

• Size—This is the size (in bytes) of every file in this package. It might make your decision to erase an unused package easier if you see six or more digits here.
• Summary—This is a concise description of the packaged software.
• Description—This is a verbose description of the packaged software. Some descriptions might be more, well, descriptive than others, but hopefully it will be enough to clue you in as to the software's role in the greater scheme of things.
• Distribution—The word Distribution is really not the best name for this field. Product might be a better choice. In any case, this is the name of the product this package is a part of.
• Vendor—The organization responsible for building this package.
• Build Date—The time the package was created.
• Build Host—The name of the computer system that built the package. Note to software packagers: Choose your build machine names wisely! A silly or offensive name might be embarrassing.
• Source RPM—The process of building a package results in two files:
  • The package file used to install the packaged software. This is sometimes called the binary package.
  • The package file containing the source code and other files used to create the binary package file. This is known as the source RPM package file. This is the filename that is displayed in this field.

    Unless you want to make changes to the software, you probably won't need to worry about source packages. But if you do, stick around because the second part of this book is for you.

Adding -l to rpm -q tells RPM to display the list of files that are installed by the specified package or packages. If you've used ls before, you won't be surprised by RPM's file list.

Here's a look at one of the smaller packages on Red Hat Linux—adduser:

# rpm -ql adduser

/usr/sbin/adduser

#

The adduser package consists of only one file, so there's only one filename displayed.

In some cases, the -v option can be added to a query command for additional information. The -l option we've been discussing is an example of just such a case. Note how the -v option adds verbosity: