Preuninstall

Preuninstall, often written as pre-uninstall or preun, refers to a packaging phase or script that runs before a software package is removed from a system. It is intended to allow cleanup, preparation, or final checks prior to the deletion of package files.

In RPM-based distributions, such as Red Hat, Fedora, and CentOS, the preuninstall step is implemented as a scriptlet named %preun. This script runs before the package’s files are removed, and is followed by a %postun script after the removal. Typical tasks for a preun script include stopping services started by the package, releasing resources, migrating or backing up data that should be preserved, and coordinating with other packages. Scriptlets should be idempotent, avoid user prompts, and fail gracefully if cleanup cannot be completed.

Debian-based systems use a related mechanism called prerm (pre-removal), which serves a similar purpose within the dpkg tooling. The exact semantics and naming differ across packaging ecosystems, but the core idea remains: execute critical steps before the package’s files are deleted.

Common tasks performed in preuninstall phases include stopping daemons, cleaning up runtime state, notifying other components of the impending removal, and validating conditions to ensure safe uninstallation. Best practices emphasize minimal, reversible changes when possible, clear logging, avoiding user interaction during automated uninstall processes, and thorough testing to handle upgrade and downgrade scenarios.

Limitations and scope should be noted: not all uninstall operations trigger a preuninstall phase, and some systems may bypass or alter scriptlet execution during certain operations (such as forced removals). See also: postuninstall, preinstall, prerm, and other packaging scriptlets.