Linux server administration/apt

Advanced Package Tool, or APT, is a free software user interface that works with core libraries to handle the installation and removal of software on Debian, Ubuntu and other Linux distributions. Main Advanced Package Tool (APT) binaries are: apt, apt-get and apt-cache

Basic apt-get/apt commands

Installing: apt install PACKAGE_NAME
apt show PACKAGE_NAME or aptitude show PACKAGE_NAME
apt policy PACKAGE_NAME ^[1] Provides source repository for a given package.
apt-get update && apt-get upgrade
Showing pending to update packages: apt-get upgrade --dry-run or apt-get upgrade -s
- /usr/lib/update-notifier/apt-check --human-readable

Basic apt-cache commands

apt-cache search
apt-cache policy^[2] List source repository configured included priorities of each source.
apt-cache showpkg PACKAGE_NAME. See also: apt show PACKAGE_NAMEdpkg -s PACKAGE_NAME

Relevant configuration files and directories

/etc/apt/sources.list^[3]: Configuration files with locations to fetch packages from.
/etc/apt/sources.list.d/: directory with additional source list fragments.

Updates

To collect information about what installed packages can be upgraded:
- apt update
- apt list --upgradable
- apt-get upgrade --dry-run or apt-get upgrade -s
- apt update && apt-upgrade
To upgrade all installed packages: apt upgrade
apt dist-upgrade (see also do-release-upgrade)
apt Automatic updates

Holding packages

To avoid packages from being upgrade when upgrading use apt-mark command

apt-mark hold PACKAGE_NAME
apt-mark unhold PACKAGE_NAME
apt-mark showhold^[4]

Single upgrade

To upgrade only a package: apt-get install --only-upgrade PACKAGE_NAME

Activities

Read differences between apt upgrade and apt dist-upgrade: https://unix.stackexchange.com/a/304887
Read Linux server administration/apt/Automatic updates
Install software-properties-common package^[5] to be able to use apt-add-repository Python command available since 2004.