Packages

apt / dpkg — package management

Installing, upgrading, and removing packages on Debian/Ubuntu; apt and dpkg.

snap — Ubuntu packages

Ubuntu's second package format with auto-update; snap revert rolls back to the previous version, kept by snap itself.

unattended-upgrades: security updates with no one at the keyboard

Ubuntu's service that installs updates from allowed origins once a day on an apt timer; by default only security ones.

Container images — layers, tags, registries and digests

An image is a read-only stack of layers with files and run settings; Docker creates containers from it.