1

This question is very fundamental. But I don't see it answered here. What is the difference between installing a .deb file and installing a package via sudo apt-get install

When I am going to download for eg ;OSMC here, they have both the options as choice. Is there any benefit from choosing one over the other? What is the technical difference?

2

A deb file is a type of format for the packaging Linux programs - specific to Debian-based distributions (in the way in Windows you have the "exe" files). It can be downloaded on your computer and installed.

The installation can be

  1. manual (one of the options you mention), when you download the deb and then install with a specialized program, or
  2. automatic (the deb is downloaded and installed by a program).

Among the programs (GUI or CLI) that can manage the installation some

  • can do both those things (GUI: Ubuntu Software Center, Discover; CLI: apt, apt-get;

  • can only install from a local deb file (GUI: Gdebi, Qapt; CLI: dpkg, which is the base for all the other tools mentioned here - as said in the other answer);

  • can only download & install automatically (that's just GUI: Synaptic, Apper, Muon).

So, apt or apt-get (like their GUI equivalents Ubuntu Software Center and Discover) can download the deb packages before installing them if the specific software source (or "repository") is already registered to your system or if you add it yourself OR they can install a program from a deb file that you already have.

Is there any benefit from choosing one over the other? What is the technical difference?

The main difference is not between the way installation is done in the two cases, but in the origin of the deb file. Just as you can download a file from the internet from a trusted or a less-trusted source, repositories are of different categories. The main difference is between official system sources (those provided by Ubuntu) and those provided by third parties.

There is no point in installing from local file a program that is available in repositories unless you lack internet connection, or you want to install a program version that is not in the repositories.

Usually the main reason for adding a new repo or installing from a local file is the absence in repos of a program or of a certain version of a program.

Remember: on Ubuntu sudo apt install command installs from deb anyway. The difference is whether you have the deb already on your computer or the installer will download it for you. In the latter case deb file are downloaded at /var/cache/apt/archives.

Deb files can be found not only on the internet, in some cases they can also be created from sources or converted from other formats (namely from rpm packages - specific to RedHat/Fedora - based distributions).

3

A .deb file is a package containing all the needed files for the application, plus some utility files used for installation/removal, etc.
These are installed via dpkg, the "Debian Package Manager".

apt-get is a frontend to dpkg (as is apt, aptitute, ...). Simply said apt downloads the .deb from known repository sources and calls dpkg under the hood to execute actions on them (i.e. install, remove, purge, etc.).

But it's not all! The apt family do a lot of extra things for you.

  • It make sure the repository cache is up to date (apt update), so it will always install the "latest" version available for your OS.
  • It automatically resolves dependencies for you, so you won't have to look around the Internet for the correct .deb files to install (and their correct version) to satisfy the dependencies of the .deb you want to install.
  • The same dependency resolution helps you when you want to remove a package. apt suggests you which other packages were installed as dependencies (or you can instruct it to remove them automatically).

Usually, you'll want to use apt, as it keeps (or at least it tries hard!) your system clean and functional. There are cases where the "download .deb file manually and install via dpkg is preferable.
Obvioulsy, if the package maintainer does not publish it on the official repositories, nor on any PPA, nor has any interest of providing a repository. In this case the only option is download + dpkg.
Or maybe, you customized your system in some non-standard way, so you need to install and manage the package manually as apt gets "confused" and cannot resolve conflicts/dependencies/etc...

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