APT – the basics

Posted on July 4, 2019 by Tom Hamilton
Reading Time: 2 minutes

Last Edited: 10/15/2022

APT stands for Advanced Package Tool and is a standard for developing and pushing packages out. There are three portions to this which is apt, apg-get and apt-cache. apt is a front end to dpkg. This means that apt serves the Debian, Ubuntu, and related Distributions.

Updating Software

apt update

The “apt update” command is used to communicate with repositories to see what is present. This can take the form of packages you have not installed yet, or if there are updates to packages that you have installed. When discussing installing any software packages like NFS, Apache; or whatever, one of the first order of operations is generally to run apt-update to make sure any remaining commands or requests is done with the most up to date information.

Installing Software

Installing a package can be as simple as, well using the keyword install and then the name of the package or the full name of the deb/file.

apt install hello.deb

Listing the installed packages

Listing the installed packages can be as simple as using the keyword list and –installed to obtain a list.

apt list --installed

Maintaining Software

Using apt-autoremove on occasion is prudent in order to remove old versions. This is especially helpful for maintaining systems and keeping the /boot directory down to something manageable. Failing to properly maintain the boot partition might (and often does) contribute to problems when installing newer versions of the Kernel packages (due to a lack of space)

apt autoremove

CHECKING WHAT NEEDS TO BE UPGRADED.

Apt can be used to provide a list of packages that need to be upgraded.

apt list --upgradable

FINE CONTROLS – Answers for questions you might not have thought to task.

Debian, Ubuntu and derivatives use debian package configuration system system called “debconf”. This system uses apt and dpkg to install “.deb:” files. There are a few environmental variables you might want to know in order to help automate your installments. If you are interactively executing this you can wait and interact with the updates. Sometimes you might be called away and an installation might be between points which might be bad.

export DEBIAN_FRONTEND=noninteractive
export NEEDRESTART_MODE=a

The option “q” can be used to quiet operations and forgo a progress bar.

apt upgrade -qy

APT CONFIGURATION

The APT File configuration is kept in /etc/apt

The following code overwrites “sources.list” with values more befitting an older deployment, say one you want to update but for which modern Ubuntu has passed on. Please do not use this without really being sure – and perhaps even backing the file up first. To be clear I am putting this here because I need to be reminded of it often enough. Plus it reminds me of how to use “cat” with redirections for writing contents to a file.

cat << EOF > /etc/apt/sources.list
deb http://old-releases.ubuntu.com/ubuntu/ xenial main restricted
deb http://old-releases.ubuntu.com/ubuntu/ xenial-updates main restricted
deb http://old-releases.ubuntu.com/ubuntu/ xenial universe
deb http://old-releases.ubuntu.com/ubuntu/ xenial-updates universe
EOF

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