The first and most important step is to determine what capabilities a package requires. If all the required capabilities are met, you can safely install the package (barring other things that can go wrong, such as conflicts). The requires dependencies are by far the most important.

The --requires option to the rpm –q command lists the capabilities a given package requires. The basic syntax is:

rpm –q query_options --requires packages

For example:

$ rpm -qp --requires sendmail-8.12.5-7.i386.rpm

/usr/sbin/alternatives

rpmlib(VersionedDependencies) <= 3.0.3-1

chkconfig >= 1.3

/usr/sbin/useradd

/bin/mktemp

fileutils

gawk

sed

sh-utils

procmail

bash >= 2.0

/bin/sh

/bin/sh

/bin/sh

/bin/sh

/bin/sh

rpmlib(PayloadFilesHavePrefix) <= 4.0-1

rpmlib(CompressedFileNames) <= 3.0.4-1

/bin/bash

libcrypto.so.2

libcrypt.so.1

libc.so.6

libc.so.6(GLIBC_2.0)

libc.so.6(GLIBC_2.1)

libc.so.6(GLIBC_2.1.3)

libc.so.6(GLIBC_2.2)

libdb-4.0.so

libgdbm.so.2

libhesiod.so.0

liblber.so.2

libldap.so.2

libnsl.so.1

libnsl.so.1(GLIBC_2.0)

libresolv.so.2

libresolv.so.2(GLIBC_2.0)

libresolv.so.2(GLIBC_2.2)

libsasl.so.7

libssl.so.2

This example tests an RPM package file, sendmail-8.12.5-7.i386.rpm, for the requires dependency, in other words, what capabilities the package requires. The sendmail package depends on a lot of other parts of the system, as you can see in the response to the command shown previously. Most of the dependencies are for system libraries (all the dependencies ending in .so or .so.number). This package requires other capabilities (packages in this case). It also requires the chkconfig package at a specific version, version 1.3 or higher, and the bash package at version 2.0 or higher. The sendmail package also requires a particular version of the RPM system (the rpmlib dependency).

Warning

Always check what a package requires before installing the package. You can also use the --test option when trying to install the package to first test whether the installation can proceed. See Chapter 4 for details on installing packages and the --test option. The rpm command will perform all these checks for you anyway. Checking in advance, though, with the --test option, helps avoid dependency hell with circular dependencies.

You can also check for what an installed package requires with the --requires option. For example:

rpm -q --requires sendmail

You can use the -R short option in place of the --requires option.

This command returns the same data as the previous command but queries an installed package rather than an RPM package file.

You might assume that applications have the most dependencies, which is true. But even source packages may depend on other packages, often the packages needed to build the sources into an application. For example, the following command lists the capabilities required by a source RPM:

$ rpm -qp --requires telnet-0.17-23.src.rpm

ncurses-devel

Some packages require particular versions of other packages, for example:

rpm -qp --requires xcdroast-0.98a9-18.src.rpm

imlib-devel >= 1.9.13-9

gtk+-devel >= 1.2.10

desktop-file-utils >= 0.2.92

rpmlib(CompressedFileNames) <= 3.0.4-1

This example shows that the xcdroast source package requires the imlib-devel capability (in this case, a package) at version 1.9.13-9 or higher, the gtk+-devel package at version 1.2.10 or higher, and the desktop-file-utils package at version 0.2.92 or higher. This is a more stringent requirement than just depending on the given packages being installed. This RPM is also an older RPM package, based on the requirement for the rpmlib to be prior or equal to 3.0.4-1.

Some packages may require a particular version of the rpmlib, or RPM library. For example, the setup package contains special system configuration files, including the default password file, /etc/passwd.

$ rpm -q --requires setup

rpmlib(PayloadFilesHavePrefix) <= 4.0-1

rpmlib(CompressedFileNames) <= 3.0.4-1

As shown in this example, this package depends only on capabilities of the RPM system itself. The particular requirements shown here specify how the rpm command should treat the package payload, including how the files are listed in the package and what type of compression is used.

Packages require capabilities, and they can provide capabilities for other packages to require. To list the capabilities a package provides, use the --provides option. These capabilities can be arbitrary names, shared libraries (.so files), and the package name itself. The basic syntax is:

rpm –q query_options --provides packages

For example, the tcsh shell package provides two capabilities, at a particular version number, as shown following:

$ rpm -q --provides tcsh

csh = 6.12

tcsh = 6.12-2

Other packages provide a lot more, including shared libraries. The httpd package provides a long list of capabilities, as shown following:

$ rpm -q --provides httpd

webserver

httpd-mmn = 20020628

libapr.so.0

libaprutil.so.0

mod_access.so

mod_actions.so

mod_alias.so

mod_asis.so

mod_auth_anon.so

mod_auth_dbm.so

mod_auth_digest.so

mod_auth.so

mod_autoindex.so

mod_cern_meta.so

mod_cgi.so

mod_dav_fs.so

mod_dav.so

mod_deflate.so

mod_dir.so

mod_env.so

mod_expires.so

mod_headers.so

mod_imap.so

mod_include.so

mod_info.so

mod_log_config.so

mod_mime_magic.so

mod_mime.so

mod_negotiation.so

mod_proxy_connect.so

mod_proxy_ftp.so

mod_proxy_http.so

mod_proxy.so

mod_rewrite.so

mod_setenvif.so

mod_speling.so

mod_status.so

mod_suexec.so

mod_unique_id.so

mod_userdir.so

mod_usertrack.so

mod_vhost_alias.so

httpd = 2.0.40-8

Use the --conflicts option to check what conflicts with a given package. The basic syntax is:

rpm –q query_options --conflicts packages

For example:

# rpm -q --conflicts httpd

thttpd

This command tells you that the httpd package (the Apache Web server) conflicts with the thttpd package. Both packages provide a similar capability. By marking the conflict, the httpd package tells you that you cannot normally install both the httpd and thttpd packages on a system. This information comes from the httpd package, which has an entry in the package that indicates the conflict. The conflict is not guaranteed. These packages may work together, but the creator of the httpd package felt that httpd would not work with the thttpd package and helpfully let us all know.

The RPM system will report on the conflicts and indicate an error if you try to install conflicting packages. The idea of conflicts really gives package creators a way to alert users to potential problems and to tell us that one package likely won’t work with another.

The force options discussed in Chapter 4 allow you to override conflicts, if absolutely necessary. In most cases, though, a conflict presents you with the choice to install one or the other of the packages, but not both.

In addition to querying capabilities and requirements of a particular package, you can query the capabilities themselves. This function allows you to check which packages require a given capability.

The --whatrequires option tells the rpm command to report on which packages in the RPM database require a certain capability. The basic syntax is:

rpm –q query_options --whatrequires capability

Some packages are not required by anything:

$ rpm -q --whatrequires tcsh

no package requires tcsh

Note

Don’t worry about the poor tcsh package being lonely. Because other packages do not require this package, you can easily remove the tcsh package without affecting the rest of your system.

This example shows a package name as the capability. Shared libraries are also considered capabilities. You can query on these as well. For example:

$ rpm -q --whatrequires librpm-4.1.so

rpm-4.1-1.06

net-snmp-5.0.1-6

rpm-python-4.1-1.06

rpm-devel-4.1-1.06

rpm-build-4.1-1.06

This example shows that the core RPM library is used by a number of RPM-related packages, along with, oddly enough, the net-snmp system-management package.

The capability you query for must be an explicit capability. For example, you will get different results if you query for the bash package or the command, /bin/bash. If you query for the bash package, you will see the packages that explicitly require the capability bash. For example:

$ rpm -q --whatrequires bash

gpm-1.19.3-20

info-4.0b-3

initscripts-6.40-1

sendmail-8.11.6-3

sysklogd-1.4.1-4

vixie-cron-3.0.1-63

ypbind-1.8-1

ypserv-1.3.12-2

If you instead query for the capability /bin/bash, that is, the file /bin/bash, you will see a different list of packages. For example:

$ rpm -q --whatrequires /bin/bash

apmd-3.0final-34

at-3.1.8-20

autofs-3.1.7-21

autofs-3.1.7-21

bash-2.05-8

bind-9.1.3-4

cipe-1.4.5-6

crontabs-1.10-1

dialog-0.9a-5

gpm-1.19.3-20

hotplug-2001_04_24-11

initscripts-6.40-1

ipchains-1.3.10-10

iproute-2.2.4-14

kudzu-0.99.23-1

logwatch-2.1.1-3

man-1.5i2-6

mkbootdisk-1.4.2-3

mkinitrd-3.2.6-1

mutt-1.2.5i-17

openssh-server-3.1p1-2

pine-4.44-1.72.0

rpm-build-4.0.3-1.03

rusers-server-0.17-12

sendmail-8.11.6-3

shapecfg-2.2.12-7

sharutils-4.2.1-8

sysklogd-1.4.1-4

tetex-1.0.7-30

ucd-snmp-4.2.1-7

vixie-cron-3.0.1-63

xinetd-2.3.3-1

ypbind-1.8-1

ypserv-1.3.12-2

There is no short form for the --whatrequires option.

Other capabilities, especially system-level shared libraries, are used by a large number of packages. For example:

# rpm -q --whatrequires libcrypt.so.1 | sort

autofs-3.1.7-21

cvs-1.11.1p1-3

cyrus-sasl-1.5.24-23

cyrus-sasl-devel-1.5.24-23

cyrus-sasl-plain-1.5.24-23

fetchmail-5.9.0-1

ircii-4.4Z-7

krbafs-1.0.9-2

nss_ldap-172-2

openldap12-1.2.12-4

openldap-2.0.11-13

openldap-clients-2.0.11-13

pam-0.75-19

pam_krb5-1.46-1

passwd-0.64.1-7

perl-5.6.0-17

pine-4.44-1.72.0

pwdb-0.61.1-3

python-1.5.2-35

rsh-0.17-5

rsh-server-0.17-5

screen-3.9.9-3

sendmail-8.11.6-3

shadow-utils-20000902-4

sh-utils-2.0.11-5

SysVinit-2.78-19

tcsh-6.10-6

util-linux-2.11f-17

vim-enhanced-5.8-7

wu-ftpd-2.6.1-20

xinetd-2.3.3-1

ypserv-1.3.12-2

yp-tools-2.5-1

Quite a few packages require encryption and decryption (the purpose of this library), making this library crucial to operating the system. Many of the packages listed here are in turn depended on by even more packages.

To help trace back capabilities, you can combine the queries. For example:

$ rpm -q --provides sendmail

smtpdaemon

sendmail = 8.11.6-3

$ rpm -q --whatrequires smtpdaemon

fetchmail-5.9.0-1

mutt-1.2.5i-17

The first command lists the capabilities that the sendmail package provides, including the generic capability of smtpdaemon. You can then list which packages require this particular capability, as shown in the second command. This is a big help for wading through a mess of packages depending on packages depending on yet more packages.

To complete the circle, you can query for which package provides a certain capability. This knowledge allows you to trace a requirement back to the package that provides it.

The --whatprovides option tells the rpm command to list the capabilities a package provides. Use the --whatprovides option with the –q, or query, option to the rpm command. (There is no short form for the --whatrprovides option.)

The basic syntax follows:

rpm –q --whatprovides capability

For example, to query what package provides the capability webserver, use the following command:

$ rpm -q --whatprovides webserver

httpd-2.0.40-8

In this case, the capability is identified by an arbitrary string, webserver. This is a generic name for a given capability, serving Web pages.

You can also trace individual files using the --whatprovides option. For example:

$ rpm -q --whatprovides /etc/skel/.bashrc

bash-2.05-8

Note

The rpm –qf command, covered in the last chapter, is an easier way to get to the same information when tracking which package provides a particular file. For example:

rpm -qf /etc/skel/.bashrc

bash-2.05-8

If you are querying particular files, use rpm –qf. If you are querying capabilities, use --whatprovides.