obsoletesprovides

Obsoletes and Provides are metadata fields used by many Linux package management systems to describe relationships between packages. The combined concept of these fields—sometimes informally referred to as obsoletesprovides—covers how a package can declare both a virtual capability and a replacement for another package.

Provides is used to declare that a package offers a given virtual package or capability. This allows dependencies to be expressed in terms of abstract features rather than concrete package names, enabling substitutions among multiple actual packages that deliver the same functionality. For example, a mail transport agent might declare Provides: mail-transport-agent, so any package that depends on that capability can be satisfied by any suitable MTA without caring which specific one is installed.

Obsoletes is used to indicate that a package supersedes or replaces one or more other packages. When a package with an Obsoletes field is installed, the package manager may remove or deprioritize the obsoleted packages to avoid conflicts and to encourage a migration path. This is commonly used during transitions, for example when a new package replaces an older one as the preferred implementation.

In practice, maintainers often combine Provides and Obsoletes (and sometimes Replaces) to smooth upgrades and transitions. A newer package might Provides: mail-transport-agent to satisfy existing dependencies, while Obsoletes: old-mta communicates that the old package is superseded. Best practices include explicitly declaring the virtual capability with Provides and carefully using Obsoletes with or without Replaces to ensure clean upgrades and minimal breakage for users.

Notes: The exact behavior depends on the package management system (for example, Debian-based dpkg/apt versus RPM-based tools), but the general concepts of virtual provides and replacement through obsoletes are widely supported.