Datasheet

Part I ✦ The Fundamentals

most users find the most compelling aspect of Debian to be its package manage-

ment system. This subsection discusses its particular properties in detail.

Package relationships

The quality of a package in Debian has a lot to do with how well it declares its rela-

tionships to other packages, and there certainly can be a lot of relationships to

declare. The full list of package relationships available for a Debian package to

declare includes Depends, Pre-Depends, Recommends, Suggests, Conflicts, Provides,

and Replaces. Table 4-1 describes how each of these fields is used.

Table 4-1

Package Relationships

Relationship Field Description and Usage

Depends If package A requires package B for use by the user, or if package B

is required for package A to be configured, package A must declare

that it Depends on package B.

Pre-Depends If package A’s installation procedure requires package B, package A

must declare that it Pre-Depends upon package B.

Recommends When package A’s functionality is enhanced with an additional

package, B, then package A must declare that it Recommends the

installation of package B.

Suggests The Suggests relationship is a weaker form of the Recommends

relationship. It’s usually used to indicate that some related software

can be used alongside the package declaring the relationship.

Conflicts When package A absolutely can not exist on the user’s machine at

the same time as package B, package A must declare that it Conflicts

with package B.

Provides When package A provides identical functionality to package B, it may

declare that it Provides package B. Therefore, when a package

Depends on package B, its dependency may be satisfied by package

A or B.

Replaces Occasionally, as when a package maintainer is reorganizing a set of

closely related packages, package A will contain the same files as

another package, B. When this is the case, package A declares that it

Replaces package B, and any files from package A will overwrite files

in package B. Without this relationship being declared, if two

packages claim the same file, the package management system will

produce an error and abort the operation.

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