A package archive normally contains metadata such as name, version, vendor, checksum and a list of dependencies.

apt-get is the Debian package file format (the .deb file).

RPM (Red Hat Package Manager) is associated with the Linux Standard Base packaging format and underpins many other tools (yum, dnf, zypper, etc.).

dpkg was originally used by Ubuntu and later adopted by Debian.

pacman (used by Arch Linux) and Entropy (used by Sabayon) both use the same tbz2 binary package format.

User encrypted passwords are stored in /etc/passwd on modern Linux systems.

The /etc/passwd file includes the user's login name, uid and gid fields, home directory and shell.

useradd is the interactive, skel-driven helper that prompts you for settings; adduser is the manual one-line tool.

Using userdel -r username will remove the user account and also delete their home directory and contents (if supported).

Netplan YAML configured with renderer: networkd and dhcp4: true sets an interface to use DHCP for IPv4.

Because systemd-resolved manages DNS, you should routinely edit /etc/resolv.conf directly to change name servers.

Traditionally /etc/resolv.conf could contain both nameserver IP addresses and search (default search domains).

RPM cannot be used to build packages; it can only install and remove them.

A package manager’s core job is automating install/upgrade/configure/remove actions and keeping a database of dependencies and versions to prevent mismatches.