Package manager

The tool that installs, updates and removes software.

A package manager installs software with its dependencies from signed repositories, tracks what belongs to what, and keeps everything upgradable with one command. apt on Debian and Ubuntu, dnf on Fedora and RHEL, pacman on Arch, apk on Alpine.

The concepts transfer between them: refresh the catalog, resolve dependencies, install from a trusted repository, and remove cleanly. Installing software by downloading random binaries bypasses all of that, and all of its security.

See it in practice

$ apt list --installed 2>/dev/null | wc -l

Counts every package the manager is tracking: a few thousand on a typical system, all upgradable with one command.

Where you'll meet it

apt

Search, install, upgrade and remove packages, plus the dnf/pacman equivalents.

Distribution (distro)

The kernel plus everything else, packaged as a usable system.

sudo & su

Temporary privilege, audited, and why sudo won everywhere.

Learn these concepts by typing them: the interactive course builds them up lesson by lesson in a real simulated shell.